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• Thread.Interrupt Is Evil

  - by Alois Kraus

  Recently I have found an interesting issue with Thread.Interrupt during application shutdown. Some application was crashing once a week and we had not really a clue what was the issue. Since it happened not very often it was left as is until we have got some memory dumps during the crash. A memory dump usually means WindDbg which I really like to use (I know I am one of the very few fans of it).  After a quick analysis I did find that the main thread already had exited and the thread with the crash was stuck in a Monitor.Wait. Strange Indeed. Running the application a few thousand times under the debugger would potentially not have shown me what the reason was so I decided to what I call constructive debugging. I did create a simple Console application project and try to simulate the exact circumstances when the crash did happen from the information I have via memory dump and source code reading. The thread that was  crashing was actually MS code from an old version of the Microsoft Caching Application Block. From reading the code I could conclude that the main thread did call the Dispose method on the CacheManger class which did call Thread.Interrupt on the cache scavenger thread which was just waiting for work to do. My first version of the repro looked like this   static void Main(string[] args) { Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); } static void ThreadFunc() { while (true) { object value = Dequeue(); // block until unblocked or awaken via ThreadInterruptedException } } static object WaitObject = new object(); static object Dequeue() { object lret = "got value"; try { lock (WaitObject) { } } catch (ThreadInterruptedException) { Console.WriteLine("Got ThreadInterruptException"); lret = null; } return lret; } I do start a background thread and call Thread.Interrupt on it and then directly let the application terminate. The thread in the meantime does plenty of Monitor.Enter/Leave calls to simulate work on it. This first version did not crash. So I need to dig deeper. From the memory dump I did know that the finalizer thread was doing just some critical finalizers which were closing file handles. Ok lets add some long running finalizers to the sample. class FinalizableObject : CriticalFinalizerObject { ~FinalizableObject() { Console.WriteLine("Hi we are waiting to finalize now and block the finalizer thread for 5s."); Thread.Sleep(5000); } } class Program { static void Main(string[] args) { FinalizableObject fin = new FinalizableObject(); Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); GC.KeepAlive(fin); // prevent finalizing it too early // After leaving main the other thread is woken up via Thread.Abort // while we are finalizing. This causes a stackoverflow in the CLR ThreadAbortException handling at this time. } With this changed Main method and a blocking critical finalizer I did get my crash just like the real application. The funny thing is that this is actually a CLR bug. When the main method is left the CLR does suspend all threads except the finalizer thread and declares all objects as garbage. After the normal finalizers were called the critical finalizers are executed to e.g. free OS handles (usually). Remember that I did call Thread.Interrupt as one of the last methods in the Main method. The Interrupt method is actually asynchronous and does wake a thread up and throws a ThreadInterruptedException only once unlike Thread.Abort which does rethrow the exception when an exception handling clause is left. It seems that the CLR does not expect that a frozen thread does wake up again while the critical finalizers are executed. While trying to raise a ThreadInterrupedException the CLR goes down with an stack overflow. Ups not so nice. Why has this nobody noticed for years is my next question. As it turned out this error does only happen on the CLR for .NET 4.0 (x86 and x64). It does not show up in earlier or later versions of the CLR. I have reported this issue on connect here but so far it was not confirmed as a CLR bug. But I would be surprised if my console application was to blame for a stack overflow in my test thread in a Monitor.Wait call. What is the moral of this story? Thread.Abort is evil but Thread.Interrupt is too. It is so evil that even the CLR of .NET 4.0 contains a race condition during the CLR shutdown. When the CLR gurus can get it wrong the chances are high that you get it wrong too when you use this constructs. If you do not believe me see what Patrick Smacchia does blog about Thread.Abort and List.Sort. Not only the CLR creators can get it wrong. The BCL writers do sometimes have a hard time with correct exception handling as well. If you do tell me that you use Thread.Abort frequently and never had problems with it I do suspect that you do not have looked deep enough into your application to find such sporadic errors.

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• Add Widget via Action in Toolbar

  - by Geertjan

  The question of the day comes from Vadim, who asks on the NetBeans Platform mailing list: "Looking for example showing how to add Widget to Scene, e.g. by toolbar button click." Well, the solution is very similar to this blog entry, where you see a solution provided by Jesse Glick for VisiTrend in Boston: https://blogs.oracle.com/geertjan/entry/zoom_capability Other relevant articles to read are as follows: http://netbeans.dzone.com/news/which-netbeans-platform-action http://netbeans.dzone.com/how-to-make-context-sensitive-actions Let's go through it step by step, with this result in the end, a solution involving 4 classes split (optionally, since a central feature of the NetBeans Platform is modularity) across multiple modules: The Customer object has a "name" String and the Droppable capability has a method "doDrop" which takes a Customer object: public interface Droppable {    void doDrop(Customer c);} In the TopComponent, we use "TopComponent.associateLookup" to publish an instance of "Droppable", which creates a new LabelWidget and adds it to the Scene in the TopComponent. Here's the TopComponent constructor: public CustomerCanvasTopComponent() {    initComponents();    setName(Bundle.CTL_CustomerCanvasTopComponent());    setToolTipText(Bundle.HINT_CustomerCanvasTopComponent());    final Scene scene = new Scene();    final LayerWidget layerWidget = new LayerWidget(scene);    Droppable d = new Droppable(){        @Override        public void doDrop(Customer c) {            LabelWidget customerWidget = new LabelWidget(scene, c.getTitle());            customerWidget.getActions().addAction(ActionFactory.createMoveAction());            layerWidget.addChild(customerWidget);            scene.validate();        }    };    scene.addChild(layerWidget);    jScrollPane1.setViewportView(scene.createView());    associateLookup(Lookups.singleton(d));} The Action is displayed in the toolbar and is enabled only if a Droppable is currently in the Lookup: @ActionID(        category = "Tools",        id = "org.customer.controler.AddCustomerAction")@ActionRegistration(        iconBase = "org/customer/controler/icon.png",        displayName = "#AddCustomerAction")@ActionReferences({    @ActionReference(path = "Toolbars/File", position = 300)})@NbBundle.Messages("AddCustomerAction=Add Customer")public final class AddCustomerAction implements ActionListener {    private final Droppable context;    public AddCustomerAction(Droppable droppable) {        this.context = droppable;    }    @Override    public void actionPerformed(ActionEvent ev) {        NotifyDescriptor.InputLine inputLine = new NotifyDescriptor.InputLine("Name:", "Data Entry");        Object result = DialogDisplayer.getDefault().notify(inputLine);        if (result == NotifyDescriptor.OK_OPTION) {            Customer customer = new Customer(inputLine.getInputText());            context.doDrop(customer);        }    }} Therefore, when the Properties window, for example, is selected, the Action will be disabled. (See the Zoomable example referred to in the link above for another example of this.) As you can see above, when the Action is invoked, a Droppable must be available (otherwise the Action would not have been enabled). The Droppable is obtained in the Action and a new Customer object is passed to its "doDrop" method. The above in pictures, take note of the enablement of the toolbar button with the red dot, on the extreme left of the toolbar in the screenshots below: The above shows the JButton is only enabled if the relevant TopComponent is active and, when the Action is invoked, the user can enter a name, after which a new LabelWidget is created in the Scene. The source code of the above is here: http://java.net/projects/nb-api-samples/sources/api-samples/show/versions/7.3/misc/WidgetCreationFromAction Note: Showing this as an MVC example is slightly misleading because, depending on which model object ("Customer" and "Droppable") you're looking at, the V and the C are different. From the point of view of "Customer", the TopComponent is the View, while the Action is the Controler, since it determines when the M is displayed. However, from the point of view of "Droppable", the TopComponent is the Controler, since it determines when the Action, i.e., which is in this case the View, displays the presence of the M.

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• .NET Code Evolution

  - by Alois Kraus

  Originally posted on: http://geekswithblogs.net/akraus1/archive/2013/07/24/153504.aspxAt my day job I do look at a lot of code written by other people. Most of the code is quite good and some is even a masterpiece. And there is also code which makes you think WTF… oh it was written by me. Hm not so bad after all. There are many excuses reasons for bad code. Most often it is time pressure followed by not enough ambition (who cares) or insufficient training. Normally I do care about code quality quite a lot which makes me a (perceived) slow worker who does write many tests and refines the code quite a lot because of the design deficiencies. Most of the deficiencies I do find by putting my design under stress while checking for invariants. It does also help a lot to step into the code with a debugger (sometimes also Windbg). I do this much more often when my tests are red. That way I do get a much better understanding what my code really does and not what I think it should be doing. This time I do want to show you how code can evolve over the years with different .NET Framework versions. Once there was  time where .NET 1.1 was new and many C++ programmers did switch over to get rid of not initialized pointers and memory leaks. There were also nice new data structures available such as the Hashtable which is fast lookup table with O(1) time complexity. All was good and much code was written since then. At 2005 a new version of the .NET Framework did arrive which did bring many new things like generics and new data structures. The “old” fashioned way of Hashtable were coming to an end and everyone used the new Dictionary<xx,xx> type instead which was type safe and faster because the object to type conversion (aka boxing) was no longer necessary. I think 95% of all Hashtables and dictionaries use string as key. Often it is convenient to ignore casing to make it easy to look up values which the user did enter. An often followed route is to convert the string to upper case before putting it into the Hashtable. Hashtable Table = new Hashtable(); void Add(string key, string value) { Table.Add(key.ToUpper(), value); } This is valid and working code but it has problems. First we can pass to the Hashtable a custom IEqualityComparer to do the string matching case insensitive. Second we can switch over to the now also old Dictionary type to become a little faster and we can keep the the original keys (not upper cased) in the dictionary. Dictionary<string, string> DictTable = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase); void AddDict(string key, string value) { DictTable.Add(key, value); } Many people do not user the other ctors of Dictionary because they do shy away from the overhead of writing their own comparer. They do not know that .NET has for strings already predefined comparers at hand which you can directly use. Today in the many core area we do use threads all over the place. Sometimes things break in subtle ways but most of the time it is sufficient to place a lock around the offender. Threading has become so mainstream that it may sound weird that in the year 2000 some guy got a huge incentive for the idea to reduce the time to process calibration data from 12 hours to 6 hours by using two threads on a dual core machine. Threading does make it easy to become faster at the expense of correctness. Correct and scalable multithreading can be arbitrarily hard to achieve depending on the problem you are trying to solve. Lets suppose we want to process millions of items with two threads and count the processed items processed by all threads. A typical beginners code might look like this: int Counter; void IJustLearnedToUseThreads() { var t1 = new Thread(ThreadWorkMethod); t1.Start(); var t2 = new Thread(ThreadWorkMethod); t2.Start(); t1.Join(); t2.Join(); if (Counter != 2 * Increments) throw new Exception("Hmm " + Counter + " != " + 2 * Increments); } const int Increments = 10 * 1000 * 1000; void ThreadWorkMethod() { for (int i = 0; i < Increments; i++) { Counter++; } } It does throw an exception with the message e.g. “Hmm 10.222.287 != 20.000.000” and does never finish. The code does fail because the assumption that Counter++ is an atomic operation is wrong. The ++ operator is just a shortcut for Counter = Counter + 1 This does involve reading the counter from a memory location into the CPU, incrementing value on the CPU and writing the new value back to the memory location. When we do look at the generated assembly code we will see only inc dword ptr [ecx+10h] which is only one instruction. Yes it is one instruction but it is not atomic. All modern CPUs have several layers of caches (L1,L2,L3) which try to hide the fact how slow actual main memory accesses are. Since cache is just another word for redundant copy it can happen that one CPU does read a value from main memory into the cache, modifies it and write it back to the main memory. The problem is that at least the L1 cache is not shared between CPUs so it can happen that one CPU does make changes to values which did change in meantime in the main memory. From the exception you can see we did increment the value 20 million times but half of the changes were lost because we did overwrite the already changed value from the other thread. This is a very common case and people do learn to protect their  data with proper locking.   void Intermediate() { var time = Stopwatch.StartNew(); Action acc = ThreadWorkMethod_Intermediate; var ar1 = acc.BeginInvoke(null, null); var ar2 = acc.BeginInvoke(null, null); ar1.AsyncWaitHandle.WaitOne(); ar2.AsyncWaitHandle.WaitOne(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Intermediate did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Intermediate() { for (int i = 0; i < Increments; i++) { lock (this) { Counter++; } } } This is better and does use the .NET Threadpool to get rid of manual thread management. It does give the expected result but it can result in deadlocks because you do lock on this. This is in general a bad idea since it can lead to deadlocks when other threads use your class instance as lock object. It is therefore recommended to create a private object as lock object to ensure that nobody else can lock your lock object. When you read more about threading you will read about lock free algorithms. They are nice and can improve performance quite a lot but you need to pay close attention to the CLR memory model. It does make quite weak guarantees in general but it can still work because your CPU architecture does give you more invariants than the CLR memory model. For a simple counter there is an easy lock free alternative present with the Interlocked class in .NET. As a general rule you should not try to write lock free algos since most likely you will fail to get it right on all CPU architectures. void Experienced() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); t1.Wait(); t2.Wait(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Experienced did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Experienced() { for (int i = 0; i < Increments; i++) { Interlocked.Increment(ref Counter); } } Since time does move forward we do not use threads explicitly anymore but the much nicer Task abstraction which was introduced with .NET 4 at 2010. It is educational to look at the generated assembly code. The Interlocked.Increment method must be called which does wondrous things right? Lets see: lock inc dword ptr [eax] The first thing to note that there is no method call at all. Why? Because the JIT compiler does know very well about CPU intrinsic functions. Atomic operations which do lock the memory bus to prevent other processors to read stale values are such things. Second: This is the same increment call prefixed with a lock instruction. The only reason for the existence of the Interlocked class is that the JIT compiler can compile it to the matching CPU intrinsic functions which can not only increment by one but can also do an add, exchange and a combined compare and exchange operation. But be warned that the correct usage of its methods can be tricky. If you try to be clever and look a the generated IL code and try to reason about its efficiency you will fail. Only the generated machine code counts. Is this the best code we can write? Perhaps. It is nice and clean. But can we make it any faster? Lets see how good we are doing currently. Level Time in s IJustLearnedToUseThreads Flawed Code Intermediate 1,5 (lock) Experienced 0,3 (Interlocked.Increment) Master 0,1 (1,0 for int[2]) That lock free thing is really a nice thing. But if you read more about CPU cache, cache coherency, false sharing you can do even better. int[] Counters = new int[12]; // Cache line size is 64 bytes on my machine with an 8 way associative cache try for yourself e.g. 64 on more modern CPUs void Master() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Master, 0); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Master, Counters.Length - 1); t1.Wait(); t2.Wait(); Counter = Counters[0] + Counters[Counters.Length - 1]; if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Master did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Master(object number) { int index = (int) number; for (int i = 0; i < Increments; i++) { Counters[index]++; } } The key insight here is to use for each core its own value. But if you simply use simply an integer array of two items, one for each core and add the items at the end you will be much slower than the lock free version (factor 3). Each CPU core has its own cache line size which is something in the range of 16-256 bytes. When you do access a value from one location the CPU does not only fetch one value from main memory but a complete cache line (e.g. 16 bytes). This means that you do not pay for the next 15 bytes when you access them. This can lead to dramatic performance improvements and non obvious code which is faster although it does have many more memory reads than another algorithm. So what have we done here? We have started with correct code but it was lacking knowledge how to use the .NET Base Class Libraries optimally. Then we did try to get fancy and used threads for the first time and failed. Our next try was better but it still had non obvious issues (lock object exposed to the outside). Knowledge has increased further and we have found a lock free version of our counter which is a nice and clean way which is a perfectly valid solution. The last example is only here to show you how you can get most out of threading by paying close attention to your used data structures and CPU cache coherency. Although we are working in a virtual execution environment in a high level language with automatic memory management it does pay off to know the details down to the assembly level. Only if you continue to learn and to dig deeper you can come up with solutions no one else was even considering. I have studied particle physics which does help at the digging deeper part. Have you ever tried to solve Quantum Chromodynamics equations? Compared to that the rest must be easy ;-). Although I am no longer working in the Science field I take pride in discovering non obvious things. This can be a very hard to find bug or a new way to restructure data to make something 10 times faster. Now I need to get some sleep ….

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• ASP.NET Multi-Select Radio Buttons

  - by Ajarn Mark Caldwell

  “HERESY!” you say, “Radio buttons are for single-select items!  If you want multi-select, use checkboxes!”  Well, I would agree, and that is why I consider this a significant bug that ASP.NET developers need to be aware of.  Here’s the situation. If you use ASP:RadioButton controls on your WebForm, then you know that in order to get them to behave properly, that is, to define a group in which only one of them can be selected by the user, you use the Group attribute and set the same value on each one.  For example: 1: <asp:RadioButton runat="server" ID="rdo1" Group="GroupName" checked="true" /> 2: <asp:RadioButton runat="server" ID="rdo2" Group="GroupName" /> With this configuration, the controls will render to the browser as HTML Input / Type=radio tags and when the user selects one, the browser will automatically deselect the other one so that only one can be selected (checked) at any time. BUT, if you user server-side code to manipulate the Checked attribute of these controls, it is possible to set them both to believe that they are checked. 1: rdo2.Checked = true; // Does NOT change the Checked attribute of rdo1 to be false. As long as you remain in server-side code, the system will believe that both radio buttons are checked (you can verify this in the debugger).  Therefore, if you later have code that looks like this 1: if (rdo1.Checked) 2: { 3: DoSomething1(); 4: } 5: else 6: { 7: DoSomethingElse(); 8: } then it will always evaluate the condition to be true and take the first action.  The good news is that if you return to the client with multiple radio buttons checked, the browser tries to clean that up for you and make only one of them really checked.  It turns out that the last one on the screen wins, so in this case, you will in fact end up with rdo2 as checked, and if you then make a trip to the server to run the code above, it will appear to be working properly.  However, if your page initializes with rdo2 checked and in code you set rdo1 to checked also, then when you go back to the client, rdo2 will remain checked, again because it is the last one and the last one checked “wins”. And this gets even uglier if you ever set these radio buttons to be disabled.  In that case, although the client browser renders the radio buttons as though only one of them is checked the system actually retains the value of both of them as checked, and your next trip to the server will really frustrate you because the browser showed rdo2 as checked, but your DoSomething1() routine keeps getting executed. The following is sample code you can put into any WebForm to test this yourself. 1: <body> 2: <form id="form1" runat="server"> 3: <h1>Radio Button Test</h1> 4: <hr /> 5: <asp:Button runat="server" ID="cmdBlankPostback" Text="Blank Postback" /> 6: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 7: <asp:Button runat="server" ID="cmdEnable" Text="Enable All" OnClick="cmdEnable_Click" /> 8: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 9: <asp:Button runat="server" ID="cmdDisable" Text="Disable All" OnClick="cmdDisable_Click" /> 10: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 11: <asp:Button runat="server" ID="cmdTest" Text="Test" OnClick="cmdTest_Click" /> 12: <br /><br /><br /> 13: <asp:RadioButton ID="rdoG1R1" GroupName="Group1" runat="server" Text="Group 1 Radio 1" Checked="true" /><br /> 14: <asp:RadioButton ID="rdoG1R2" GroupName="Group1" runat="server" Text="Group 1 Radio 2" /><br /> 15: <asp:RadioButton ID="rdoG1R3" GroupName="Group1" runat="server" Text="Group 1 Radio 3" /><br /> 16: <hr /> 17: <asp:RadioButton ID="rdoG2R1" GroupName="Group2" runat="server" Text="Group 2 Radio 1" /><br /> 18: <asp:RadioButton ID="rdoG2R2" GroupName="Group2" runat="server" Text="Group 2 Radio 2" Checked="true" /><br /> 19:  20: </form> 21: </body> 1: protected void Page_Load(object sender, EventArgs e) 2: { 3:  4: } 5:  6: protected void cmdEnable_Click(object sender, EventArgs e) 7: { 8: rdoG1R1.Enabled = true; 9: rdoG1R2.Enabled = true; 10: rdoG1R3.Enabled = true; 11: rdoG2R1.Enabled = true; 12: rdoG2R2.Enabled = true; 13: } 14:  15: protected void cmdDisable_Click(object sender, EventArgs e) 16: { 17: rdoG1R1.Enabled = false; 18: rdoG1R2.Enabled = false; 19: rdoG1R3.Enabled = false; 20: rdoG2R1.Enabled = false; 21: rdoG2R2.Enabled = false; 22: } 23:  24: protected void cmdTest_Click(object sender, EventArgs e) 25: { 26: rdoG1R2.Checked = true; 27: rdoG2R1.Checked = true; 28: } 29: 30: protected void Page_PreRender(object sender, EventArgs e) 31: { 32:  33: } After you copy the markup and page-behind code into the appropriate files.  I recommend you set a breakpoint on Page_Load as well as cmdTest_Click, and add each of the radio button controls to the Watch list so that you can walk through the code and see exactly what is happening.  Use the Blank Postback button to cause a postback to the server so you can inspect things without making any changes. The moral of the story is: if you do server-side manipulation of the Checked status of RadioButton controls, then you need to set ALL of the controls in a group whenever you want to change one.

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• Web Services Example - Part 2: Programmatic

  - by Denis T

  In this edition of the ADF Mobile blog we'll tackle part 2 of our Web Service examples.  In this posting we'll take a look at using a SOAP Web Service but calling it programmatically in code and parsing the return into a bean. Getting the sample code: Just click here to download a zip of the entire project.  You can unzip it and load it into JDeveloper and deploy it either to iOS or Android.  Please follow the previous blog posts if you need help getting JDeveloper or ADF Mobile installed.  Note: This is a different workspace than WS-Part1 Defining our Web Service: Just like our first installment, we are using the same public weather forecast web service provided free by CDYNE Corporation.  Sometimes this service goes down so please ensure you know it's up before reporting this example isn't working. We're going to concentrate on the same two web service methods, GetCityForecastByZIP and GetWeatherInformation. Defing the Application: The application setup is identical to the Weather1 version.  There are some improvements to the data that is displayed as part of this example though.  Now we are able to show the associated image along with each forecast line when using the Forecast By Zip feature.  We've also added the temperature Hi/Low values into the UI. Summary of Fundamental Changes In This Application The most fundamental change is that we're binding the UI to the Bean Data Controls instead of directly to the Web Service Data Controls.  This gives us much more flexibility to control the shape of the data and allows us to do caching of the data outside of the Web Service.  This way if your application is, say offline, your bean could still populate with data from a local cache and still show you some UI as opposed to completely failing because you don't have any connectivity. In general we promote this type of programming technique with ADF Mobile to insulate your application from any issues with network connectivity. What's different with this example? We have setup the Web Service DC the same way but now we have managed beans to process the data.  The following classes define the "Model" of our application:  CityInformation-CityForecast-Forecast, WeatherInformation-WeatherDescription.  We use WeatherBean for UI interaction to the model layer.  If you look through this example, we don't really do that much with the java code except use it to grab the image URL from the weather description.  In a more realistic example, you might be using some JDBC classes to persist the data to a local database. To have a good architecture it is always good to keep your model and UI layers separate.  This gets muddied if you start to use bindings on a page invoked from Java code and this java code starts to become your "model" layer.  Since bindings are page specific, your model layer starts to become entwined with your UI.  Not good!  To help with this, we've added some utility functions that let you invoke DC methods without having a binding and thus execute methods from your "model" layer without requiring a binding in your page definition.  We do this with the invokeDataControlMethod of the AdfmfJavaUtilities class.  An example of this method call is available in line 95 of WeatherInformation.java and line 93 of CityInformation.Java. What's a GenericType? Because Web Service Data Controls (and also URL Data Controls AKA REST) use generic name/value pairs to define their structure and don't have strongly typed objects, these are actually stored internally as GenericType objects.  The GenericType class is simply a property map of name/value pairs that can be hierarchical.  There are methods like getAttribute where you supply the index of the attribute or it's string property name.  Why is this important to know?  Because invokeDataControlMethod returns GenericType objects and developers either need to parse these GenericType objects themselves or use one of our helper functions. GenericTypeBeanSerializationHelper This class does exactly what it's name implies.  It's a helper class for developers to aid in serialization of GenericTypes to/from java objects.  This is extremely handy if you have a large GenericType object with many attributes (or you're just lazy like me!) and you just want to parse it out into a real java object you can use more easily.  Here you would use the fromGenericType method.  This method takes the class of the Java object you wish to return and the GenericType as parameters.  The method then parses through each attribute in the GenericType and uses reflection to set that same attribute in the Java class.  Then the method returns that new object of the class you specified.  This is obviously very handy to avoid a lot of shuffling code between GenericType and your own Java classes.  The reverse method, toGenericType is also available when you want to go the other way.  In this case you supply the string that represents the package location in the DataControl definition (Example: "MyDC.myParams.MyCollection") and then pass in the Java object you have that holds the data and a GenericType is returned to you.  Again, it will use reflection to calculate the attributes that match between the java class and the GenericType and call the getters/setters on those. Issues and Possible Improvements: In the next installment we'll show you how to make your web service calls asynchronously so your UI will fill dynamically when the service call returns but in the meantime you show the data you have locally in your bean fed from some local cache.  This gives your users instant delivery of some data while you fetch other data in the background.

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• Proxied calls not working as expected

  - by AndyH

  I have been modifying an application to have a cleaner client/server split to allow for load splitting and resource sharing etc. Everything is written to an interface so it was easy to add a remoting layer to the interface using a proxy. Everything worked fine. The next phase was to add a caching layer to the interface and again this worked fine and speed was improved but not as much as I would have expected. On inspection it became very clear what was going on. I feel sure that this behavior has been seen many times before and there is probably a design pattern to solve the problem but it eludes me and I'm not even sure how to describe it. It is easiest explained with an example. Let's imagine the interface is interface IMyCode { List<IThing> getLots( List<String> ); IThing getOne( String id ); } The getLots() method calls getOne() and fills up the list before returning. The interface is implemented at the client which is proxied to a remoting client which then calls the remoting server which in turn calls the implementation at the server. At the client and the server layers there is also a cache. So we have :- Client interface | Client cache | Remote client | Remote server | Server cache | Server interface If we call getOne("A") at the client interface, the call is passed to the client cache which faults. This then calls the remote client which passes the call to the remote server. This then calls the server cache which also faults and so the call is eventually passed to the server interface which actually gets the IThing. In turn the server cache is filled and finally the client cache also. If getOne("A") is again called at the client interface the client cache has the data and it gets returned immediately. If a second client called getOne("B") it would fill the server cache with "B" as well as it's own client cache. Then, when the first client calls getOne("B") the client cache faults but the server cache has the data. This is all as one would expect and works well. Now lets call getLots( [ "C", "D" ] ). This works as you would expect by calling getOne() twice but there is a subtlety here. The call to getLots() cannot directly make use of the cache. Therefore the sequence is to call the client interface which in turn calls the remote client, then the remote server and eventually the server interface. This then calls getOne() to fill the list before returning. The problem is that the getOne() calls are being satisfied at the server when ideally they should be satisfied at the client. If you imagine that the client/server link is really slow then it becomes clear why the client call is more efficient than the server call once the client cache has the data. This example is contrived to illustrate the point. The more general problem is that you cannot just keep adding proxied layers to an interface and expect it to work as you would imagine. As soon as the call goes 'through' the proxy any subsequent calls are on the proxied side rather than 'self' side. Have I failed to learn or not learned something correctly? All this is implemented in Java and I haven't used EJBs. It seems that the example may be confusing. The problem is nothing to do with cache efficiencies. It is more to do with an illusion created by the use of proxies or AOP techniques in general. When you have an object whose class implements an interface there is an assumption that a call on that object might make further calls on that same object. For example, public String getInternalString() { return InetAddress.getLocalHost().toString(); } public String getString() { return getInternalString(); } If you get an object and call getString() the result depends where the code is running. If you add a remoting proxy to the class then the result could be different for calls to getString() and getInternalString() on the same object. This is because the initial call gets 'deproxied' before the actual method is called. I find this not only confusing but I wonder how I can control this behavior especially as the use of the proxy may be by a third party. The concept is fine but the practice is certainly not what I expected. Have I missed the point somewhere?

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• Building a Repository Pattern against an EF 5 EDMX Model - Part 1

  - by Juan

  I am part of a year long plus project that is re-writing an existing application for a client.  We have decided to develop the project using Visual Studio 2012 and .NET 4.5.  The project will be using a number of technologies and patterns to include Entity Framework 5, WCF Services, and WPF for the client UI.This is my attempt at documenting some of the successes and failures that I will be coming across in the development of the application.In building the data access layer we have to access a database that has already been designed by a dedicated dba. The dba insists on using Stored Procedures which has made the use of EF a little more difficult.  He will not allow direct table access but we did manage to get him to allow us to use Views.  Since EF 5 does not have good support to do Code First with Stored Procedures, my option was to create a model (EDMX) against the existing database views.   I then had to go select each entity and map the Insert/Update/Delete functions to their respective stored procedure. The next step after I had completed mapping the stored procedures to the entities in the EDMX model was to figure out how to build a generic repository that would work well with Entity Framework 5.  After reading the blog posts below, I adopted much of their code with some changes to allow for the use of Ninject for dependency injection.http://www.tcscblog.com/2012/06/22/entity-framework-generic-repository/ http://www.tugberkugurlu.com/archive/generic-repository-pattern-entity-framework-asp-net-mvc-and-unit-testing-triangle IRepository.cs public interface IRepository : IDisposable where T : class { void Add(T entity); void Update(T entity, int id); T GetById(object key); IQueryable Query(Expression> predicate); IQueryable GetAll(); int SaveChanges(); int SaveChanges(bool validateEntities); } GenericRepository.cs public abstract class GenericRepository : IRepository where T : class { public abstract void Add(T entity); public abstract void Update(T entity, int id); public abstract T GetById(object key); public abstract IQueryable Query(Expression> predicate); public abstract IQueryable GetAll(); public int SaveChanges() { return SaveChanges(true); } public abstract int SaveChanges(bool validateEntities); public abstract void Dispose(); } One of the issues I ran into was trying to do an update. I kept receiving errors so I posted a question on Stack Overflow http://stackoverflow.com/questions/12585664/an-object-with-the-same-key-already-exists-in-the-objectstatemanager-the-object and came up with the following hack. If someone has a better way, please let me know. DbContextRepository.cs public class DbContextRepository : GenericRepository where T : class { protected DbContext Context; protected DbSet DbSet; public DbContextRepository(DbContext context) { if (context == null) throw new ArgumentException("context"); Context = context; DbSet = Context.Set(); } public override void Add(T entity) { if (entity == null) throw new ArgumentException("Cannot add a null entity."); DbSet.Add(entity); } public override void Update(T entity, int id) { if (entity == null) throw new ArgumentException("Cannot update a null entity."); var entry = Context.Entry(entity); if (entry.State == EntityState.Detached) { var attachedEntity = DbSet.Find(id); // Need to have access to key if (attachedEntity != null) { var attachedEntry = Context.Entry(attachedEntity); attachedEntry.CurrentValues.SetValues(entity); } else { entry.State = EntityState.Modified; // This should attach entity } } } public override T GetById(object key) { return DbSet.Find(key); } public override IQueryable Query(Expression> predicate) { return DbSet.Where(predicate); } public override IQueryable GetAll() { return Context.Set(); } public override int SaveChanges(bool validateEntities) { Context.Configuration.ValidateOnSaveEnabled = validateEntities; return Context.SaveChanges(); } #region IDisposable implementation public override void Dispose() { if (Context != null) { Context.Dispose(); GC.SuppressFinalize(this); } } #endregion IDisposable implementation } At this point I am able to start creating individual repositories that are needed and add a Unit of Work.  Stay tuned for the next installment in my path to creating a Repository Pattern against EF5.

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• How to create Captcha in ASP.NET

  - by Samir R. Bhogayta

  1. Create one page with name "Captcha.aspx" 2. No any control require in this page 3. Go to Captcha.aspx.vb write the below code Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load         'create object of Bitmap Class and set its width and height.         Dim objBMP As Bitmap = New Bitmap(180, 51)         'Create Graphics object and assign bitmap object to graphics' object.         Dim objGraphics As Graphics = Graphics.FromImage(objBMP)         objGraphics.Clear(Color.White)         objGraphics.TextRenderingHint = TextRenderingHint.AntiAlias         Dim objFont As Font = New Font("arial", 30, FontStyle.Bold)         'genetating random 6 digit random number         Dim randomStr As String = GeneratePassword()         'set this random number in session         Session.Add("randomStr", randomStr)         Session.Add("randomStrCountry", randomStr)         objGraphics.DrawString(randomStr, objFont, Brushes.Black, 2, 2)         Response.ContentType = "image/GIF"         objBMP.Save(Response.OutputStream, ImageFormat.Gif)         objFont.Dispose()         objGraphics.Dispose()         objBMP.Dispose()     End Sub     Public Function GeneratePassword() As String         ' Below code describes how to create random numbers.some of the digits and letters         ' are ommited because they look same like "i","o","1","0","I","O".         Dim allowedChars As String = "a,b,c,d,e,f,g,h,j,k,m,n,p,q,r,s,t,u,v,w,x,y,z,"         allowedChars += "A,B,C,D,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z,"         allowedChars += "2,3,4,5,6,7,8,9"         Dim sep() As Char = {","c}         Dim arr() As String = allowedChars.Split(sep)         Dim passwordString As String = ""         Dim temp As String         Dim rand As Random = New Random()         Dim i As Integer         For i = 0 To 5 - 1 Step i + 1             temp = arr(rand.Next(0, arr.Length))             passwordString += temp         Next         Return passwordString     End Function 4. Use this page in you aspx page like this img alt="" border="0" src="Captcha.aspx" style="cursor: move; height: 60px; width: 200px;" //                                   your textbox to insert code by user.

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• Problem displaying custom error page in ASP.NET MVC 2

  - by robert_d

  This is customErrors section from my web.config file <customErrors mode="On"> <error statusCode="500" redirect="HTTP500.aspx" /> </customErrors> HTTP500.aspx is the same as standard /Views/Shared/Error.aspx page. When I get HTTP 500 error I see this page: Server Error in '/' Application. Runtime Error Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed. Details: To enable the details of this specific error message to be viewable on the local server machine, please create a tag within a "web.config" configuration file located in the root directory of the current web application. This tag should then have its "mode" attribute set to "RemoteOnly". To enable the details to be viewable on remote machines, please set "mode" to "Off". Notes: The current error page you are seeing can be replaced by a custom error page by modifying the "defaultRedirect" attribute of the application's configuration tag to point to a custom error page URL. But when I change the above customErrors section like this: <customErrors mode="On"> <error statusCode="500" redirect="HTTP500.htm" /> </customErrors> then HTTP500.htm page is displayed when HTTP 500 error occurs. Why HTTP500.aspx page isn't displayed?

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• C#: Cannot handle redirect from HTTP/HTTPS protocols to other dissimilar ones

  - by Peanut

  Basically, I'm trying to grab an EXE from CNet's Download.com So i created web parser and so far all is going well. Here is a sample link pulled directly from their site: http://dw.com.com/redir?edId=3&siteId=4&oId=3001-20_4-10308491&ontId=20_4&spi=e6323e8d83a8b4374d43d519f1bd6757&lop=txt&tag=idl2&pid=10566981&mfgId=6250549&merId=6250549&pguid=PlvcGQoPjAEAAH5rQL0AAABv&destUrl=ftp%3A%2F%2F202.190.201.108%2Fpub%2Fryl2%2Fclient%2Finstaller-ryl2_v1673.exe Here is the problem: When you attempt to download, it begins with HTTP, then redirects to an FTP site. I have tried .NET's WebClient and HttpWebRequest Objects, and it looks like Neither can support Redirects. This Code Fails at GetResponse(); HttpWebRequest req = (HttpWebRequest)WebRequest.Create("http://dw.com.com/redir?edId=3&siteId=4&oId=3001-20_4-10308491&ontId=20_4&spi=e6323e8d83a8b4374d43d519f1bd6757&lop=txt&tag=idl2&pid=10566981&mfgId=6250549&merId=6250549&pguid=PlvcGQoPjAEAAH5rQL0AAABv&destUrl=ftp%3A%2F%2F202.190.201.108%2Fpub%2Fryl2%2Fclient%2Finstaller-ryl2_v1673.exe"); WebResponse response = req.GetResponse(); Now, I also tried this: HttpWebRequest req = (HttpWebRequest)WebRequest.Create("http://dw.com.com/redir?edId=3&siteId=4&oId=3001-20_4-10308491&ontId=20_4&spi=e6323e8d83a8b4374d43d519f1bd6757&lop=txt&tag=idl2&pid=10566981&mfgId=6250549&merId=6250549&pguid=PlvcGQoPjAEAAH5rQL0AAABv&destUrl=ftp%3A%2F%2F202.190.201.108%2Fpub%2Fryl2%2Fclient%2Finstaller-ryl2_v1673.exe"); req.AllowAutoRedirect = false; WebResponse response = req.GetResponse(); string s = new StreamReader(response.GetResponseStream()).ReadToEnd(); And it does not throw the error anymore, however variable s turns out to be an empty string. I'm at a loss! Can anyone help out?

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• Mimicking the UltraGridColumnChooser's drag & drop ability

  - by Sören Kuklau

  (Infragistics 2008 Vol. 3, CLR 2.0) Infragistics's UltraGrid comes with a column chooser user control, which is simply a vertical arrangement of columns with checkboxes that toggle a column's hidden state. In addition, it allows you to pick a column and drag it directly to the grid so you don't have to manually position it afterwards. (This is particularly handy when you already have a lot of visible columns and have no clue where the new one ended up.) I'm building my own column chooser based on an UltraTree. Getting the checkboxes to behave the same wasn't an issue, but I haven't found a way to drag a column from the tree to the grid and have it accept it. In my tree, each UltraTreeNode has a Tag with the following struct: Private Structure DraggableGridColumn Public NodeKey As String Public NodeName As String Public ParentKey As String Public Column As UltraGridColumn End Structure I then have an event as follows: Private Sub columnsTree_SelectionDragStart(ByVal sender As Object, ByVal e As System.EventArgs) Handles columnsTree.SelectionDragStart If columnsTree.SelectedNodes.Count <> 1 Then Return End If If Not TypeOf columnsTree.SelectedNodes(0).Tag Is DraggableGridColumn Then Return End If Dim column As UltraGridColumn = CType(columnsTree.SelectedNodes(0).Tag, DraggableGridColumn).Column columnsTree.DoDragDrop(column, DragDropEffects.All) End Sub In the DoDragDrop call, neither column (of type UltraGridColumn) nor column.Header (of type ColumnHeader) get accepted by the grid. I assume I'm sending the wrong type, and/or that the grid expects a special struct with some additional information. Unfortunately, I've also failed to catch an event (both on the column chooser side as well as on the grid side) where Infragistics's normal column chooser does this properly; the normal drag & drop events never seem to fire.

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• Flash: How to make an embedded video not autoplay

  - by jb

  I'm embedding a Flash video into an HTML and would like the user to have to click it to begin playing. According to the Adobe <object> / <embed> element documentation, there are variety of methods to do this: 1) Add a Flash parameter inside the <object> tag: <param name="play" value="false"> 2) Add the attribute play inside the <embed> tag: <embed ... play="false"> 3) Add the attribute flashvars inside the <embed> tag: <embed ... flashvars="play=false"> Which is awesome. Only ... none of them work for me: http://johnboxall.github.com/test/flash/flash.htm My code looks like this now: <object width="590" height="475"> <param name="movie" value="untitled_skin.swf"> <param name="play" value="false"> <embed src="untitled_skin.swf" width="590" height="475" type="application/x-shockwave-flash" play="false" flashvars="autoplay=false&play=false" menu="false"></embed> </object> Anyone have any ideas? What am I doing wrong?

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• ASP.NET MVC DropDownList SelectedValue works on Edit action, but not Create action

  - by davekaro

  I have the following code in my controller (for Edit and Create): model.Templates = new SelectList(PageManagementService.PageTemplateFetchList(), "PageId", "Title", 213); the "213" is an Id for one of the pages - just using it for testing. And this is in my view (for Edit and Create): <%= this.Html.DropDownListFor(model => model.Page.TemplateId, this.Model.Templates)%> <%= this.Model.Templates.SelectedValue %> When I go to the Create form, I see the dropdown list, but the tag with value="213" is not selected. I even output the SelectedValue to make sure it's 213 - and I see 213. When I go to the Edit form, I see the dropdown list, and the tag with value="213" is selected. On the Create form, none of the tags have a "selected" attribute. On the Edit form, the tag with value="213" has the "selected" attribute. Am I missing something? What could be causing this? Anyone see this behavior before?

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• XNA Xbox 360 Content Manager Thread freezing Draw Thread

  - by Alikar

  I currently have a game that takes in large images, easily bigger than 1MB, to serve as backgrounds. I know exactly when this transition is supposed to take place, so I made a loader class to handle loading these large images in the background, but when I load the images it still freezes the main thread where the drawing takes place. Since this code runs on the 360 I move the thread to the 4th hardware thread, but that doesn't seem to help. Below is the class I am using. Any thoughts as to why my new content manager which should be in its own thread is interrupting the draw in my main thread would be appreciated. namespace FileSystem { /// <summary> /// This is used to reference how many objects reference this texture. /// Everytime someone references a texture we increase the iNumberOfReferences. /// When a class calls remove on a specific texture we check to see if anything /// else is referencing the class, if it is we don't remove it. If there isn't /// anything referencing the texture its safe to dispose of. /// </summary> class TextureContainer { public uint uiNumberOfReferences = 0; public Texture2D texture; } /// <summary> /// This class loads all the files from the Content. /// </summary> static class FileManager { static Microsoft.Xna.Framework.Content.ContentManager Content; static EventWaitHandle wh = new AutoResetEvent(false); static Dictionary<string, TextureContainer> Texture2DResourceDictionary; static List<Texture2D> TexturesToDispose; static List<String> TexturesToLoad; static int iProcessor = 4; private static object threadMutex = new object(); private static object Texture2DMutex = new object(); private static object loadingMutex = new object(); private static bool bLoadingTextures = false; /// <summary> /// Returns if we are loading textures or not. /// </summary> public static bool LoadingTexture { get { lock (loadingMutex) { return bLoadingTextures; } } } /// <summary> /// Since this is an static class. This is the constructor for the file loadeder. This is the version /// for the Xbox 360. /// </summary> /// <param name="_Content"></param> public static void Initalize(IServiceProvider serviceProvider, string rootDirectory, int _iProcessor ) { Content = new Microsoft.Xna.Framework.Content.ContentManager(serviceProvider, rootDirectory); Texture2DResourceDictionary = new Dictionary<string, TextureContainer>(); TexturesToDispose = new List<Texture2D>(); iProcessor = _iProcessor; CreateThread(); } /// <summary> /// Since this is an static class. This is the constructor for the file loadeder. /// </summary> /// <param name="_Content"></param> public static void Initalize(IServiceProvider serviceProvider, string rootDirectory) { Content = new Microsoft.Xna.Framework.Content.ContentManager(serviceProvider, rootDirectory); Texture2DResourceDictionary = new Dictionary<string, TextureContainer>(); TexturesToDispose = new List<Texture2D>(); CreateThread(); } /// <summary> /// Creates the thread incase we wanted to set up some parameters /// Outside of the constructor. /// </summary> static public void CreateThread() { Thread t = new Thread(new ThreadStart(StartThread)); t.Start(); } // This is the function that we thread. static public void StartThread() { //BBSThreadClass BBSTC = (BBSThreadClass)_oData; FileManager.Execute(); } /// <summary> /// This thread shouldn't be called by the outside world. /// It allows the File Manager to loop. /// </summary> static private void Execute() { // Make sure our thread is on the correct processor on the XBox 360. #if WINDOWS #else Thread.CurrentThread.SetProcessorAffinity(new int[] { iProcessor }); Thread.CurrentThread.IsBackground = true; #endif // This loop will load textures into ram for us away from the main thread. while (true) { wh.WaitOne(); // Locking down our data while we process it. lock (threadMutex) { lock (loadingMutex) { bLoadingTextures = true; } bool bContainsKey = false; for (int con = 0; con < TexturesToLoad.Count; con++) { // If we have already loaded the texture into memory reference // the one in the dictionary. lock (Texture2DMutex) { bContainsKey = Texture2DResourceDictionary.ContainsKey(TexturesToLoad[con]); } if (bContainsKey) { // Do nothing } // Otherwise load it into the dictionary and then reference the // copy in the dictionary else { TextureContainer TC = new TextureContainer(); TC.uiNumberOfReferences = 1; // We start out with 1 referece. // Loading the texture into memory. try { TC.texture = Content.Load<Texture2D>(TexturesToLoad[con]); // This is passed into the dictionary, thus there is only one copy of // the texture in memory. // There is an issue with Sprite Batch and disposing textures. // This will have to wait until its figured out. lock (Texture2DMutex) { bContainsKey = Texture2DResourceDictionary.ContainsKey(TexturesToLoad[con]); Texture2DResourceDictionary.Add(TexturesToLoad[con], TC); } // We don't have the find the reference to the container since we // already have it. } // Occasionally our texture will already by loaded by another thread while // this thread is operating. This mainly happens on the first level. catch (Exception e) { // If this happens we don't worry about it since this thread only loads // texture data and if its already there we don't need to load it. } } Thread.Sleep(100); } } lock (loadingMutex) { bLoadingTextures = false; } } } static public void LoadTextureList(List<string> _textureList) { // Ensuring that we can't creating threading problems. lock (threadMutex) { TexturesToLoad = _textureList; } wh.Set(); } /// <summary> /// This loads a 2D texture which represents a 2D grid of Texels. /// </summary> /// <param name="_textureName">The name of the picture you wish to load.</param> /// <returns>Holds the image data.</returns> public static Texture2D LoadTexture2D( string _textureName ) { TextureContainer temp; lock (Texture2DMutex) { bool bContainsKey = false; // If we have already loaded the texture into memory reference // the one in the dictionary. lock (Texture2DMutex) { bContainsKey = Texture2DResourceDictionary.ContainsKey(_textureName); if (bContainsKey) { temp = Texture2DResourceDictionary[_textureName]; temp.uiNumberOfReferences++; // Incrementing the number of references } // Otherwise load it into the dictionary and then reference the // copy in the dictionary else { TextureContainer TC = new TextureContainer(); TC.uiNumberOfReferences = 1; // We start out with 1 referece. // Loading the texture into memory. try { TC.texture = Content.Load<Texture2D>(_textureName); // This is passed into the dictionary, thus there is only one copy of // the texture in memory. } // Occasionally our texture will already by loaded by another thread while // this thread is operating. This mainly happens on the first level. catch(Exception e) { temp = Texture2DResourceDictionary[_textureName]; temp.uiNumberOfReferences++; // Incrementing the number of references } // There is an issue with Sprite Batch and disposing textures. // This will have to wait until its figured out. Texture2DResourceDictionary.Add(_textureName, TC); // We don't have the find the reference to the container since we // already have it. temp = TC; } } } // Return a reference to the texture return temp.texture; } /// <summary> /// Go through our dictionary and remove any references to the /// texture passed in. /// </summary> /// <param name="texture">Texture to remove from texture dictionary.</param> public static void RemoveTexture2D(Texture2D texture) { foreach (KeyValuePair<string, TextureContainer> pair in Texture2DResourceDictionary) { // Do our references match? if (pair.Value.texture == texture) { // Only one object or less holds a reference to the // texture. Logically it should be safe to remove. if (pair.Value.uiNumberOfReferences <= 1) { // Grabing referenc to texture TexturesToDispose.Add(pair.Value.texture); // We are about to release the memory of the texture, // thus we make sure no one else can call this member // in the dictionary. Texture2DResourceDictionary.Remove(pair.Key); // Once we have removed the texture we don't want to create an exception. // So we will stop looking in the list since it has changed. break; } // More than one Object has a reference to this texture. // So we will not be removing it from memory and instead // simply marking down the number of references by 1. else { pair.Value.uiNumberOfReferences--; } } } } /*public static void DisposeTextures() { int Count = TexturesToDispose.Count; // If there are any textures to dispose of. if (Count > 0) { for (int con = 0; con < TexturesToDispose.Count; con++) { // =!THIS REMOVES THE TEXTURE FROM MEMORY!= // This is not like a normal dispose. This will actually // remove the object from memory. Texture2D is inherited // from GraphicsResource which removes it self from // memory on dispose. Very nice for game efficency, // but "dangerous" in managed land. Texture2D Temp = TexturesToDispose[con]; Temp.Dispose(); } // Remove textures we've already disposed of. TexturesToDispose.Clear(); } }*/ /// <summary> /// This loads a 2D texture which represnets a font. /// </summary> /// <param name="_textureName">The name of the font you wish to load.</param> /// <returns>Holds the font data.</returns> public static SpriteFont LoadFont( string _fontName ) { SpriteFont temp = Content.Load<SpriteFont>( _fontName ); return temp; } /// <summary> /// This loads an XML document. /// </summary> /// <param name="_textureName">The name of the XML document you wish to load.</param> /// <returns>Holds the XML data.</returns> public static XmlDocument LoadXML( string _fileName ) { XmlDocument temp = Content.Load<XmlDocument>( _fileName ); return temp; } /// <summary> /// This loads a sound file. /// </summary> /// <param name="_fileName"></param> /// <returns></returns> public static SoundEffect LoadSound( string _fileName ) { SoundEffect temp = Content.Load<SoundEffect>(_fileName); return temp; } } }

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• Help: Android paint/canvas issue; drawing smooth curves

  - by Wrapper

  How do I get smooth curves instead of dots or circles, when I draw with my finger on the touch screen, in Android? I am using the following code- public class DrawView extends View implements OnTouchListener { private static final String TAG = "DrawView"; List<Point> points = new ArrayList<Point>(); Paint paint = new Paint(); public DrawView(Context context) { super(context); setFocusable(true); setFocusableInTouchMode(true); this.setOnTouchListener(this); paint.setColor(Color.WHITE); paint.setAntiAlias(true); } @Override public void onDraw(Canvas canvas) { for (Point point : points) { canvas.drawCircle(point.x, point.y, 5, paint); // Log.d(TAG, "Painting: "+point); } } public boolean onTouch(View view, MotionEvent event) { // if(event.getAction() != MotionEvent.ACTION_DOWN) // return super.onTouchEvent(event); Point point = new Point(); point.x = event.getX(); point.y = event.getY(); points.add(point); invalidate(); Log.d(TAG, "point: " + point); return true; } } class Point { float x, y; @Override public String toString() { return x + ", " + y; } }

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• Process: Unable to start service com.google.android.gms.checkin.CheckinService with Intent

  - by AndyRoid

  I'm trying to build a Google map application but keep receiving this in my LogCat. I have all the permissions and meta-data set in my manifest, but am still dumbfounded by this error. Have looked everywhere on SO for this specific error but found nothing relating to com.google.android.gms.checkin A little bit about my structural hierarchy. MainActivity extends ActionBarActivity with three tabs underneath actionbar. Each tab has it's own fragment. On the gMapFragment I create a GPSTrack object from my GPSTrack class which extends Service and implements LocationListener. The problem is that when I start the application I get this message: I have all my libraries imported properly and I even added the google-play-services.jar into my libs folder. I also installed Google Play Services APKs through CMD onto my emulator. Furthermore the LocationManager lm = = (LocationManager) mContext.getSystemService(LOCATION_SERVICE); in my GPSTrack class always returns null. Why is this and how can I fix these issues? Would appreciate an explanation along with solution too, I want to understand what's going on here. ============== Code: gMapFragment.java public class gMapFragment extends SupportMapFragment { private final String TAG = "gMapFragment"; private GoogleMap mMap; protected SupportMapFragment mapFrag; private Context mContext = getActivity(); private static View view; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { if (view != null) { ViewGroup parent = (ViewGroup) view.getParent(); if (parent != null) { parent.removeView(view); } } try { super.onCreateView(inflater, container, savedInstanceState); view = inflater.inflate(R.layout.fragment_map, container, false); setupGoogleMap(); } catch (Exception e) { /* * Map already there , just return as view */ } return view; } private void setupGoogleMap() { mapFrag = (SupportMapFragment) getFragmentManager().findFragmentById( R.id.mapView); if (mapFrag == null) { FragmentManager fragManager = getFragmentManager(); FragmentTransaction fragTransaction = fragManager .beginTransaction(); mapFrag = SupportMapFragment.newInstance(); fragTransaction.replace(R.id.mapView, mapFrag).commit(); } if (mapFrag != null) { mMap = mapFrag.getMap(); if (mMap != null) { setupMap(); mMap.setOnMapClickListener(new OnMapClickListener() { @Override public void onMapClick(LatLng point) { // TODO your click stuff on map } }); } } } @Override public void onAttach(Activity activity) { super.onAttach(activity); Log.d("Attach", "on attach"); } @Override public void onDetach() { super.onDetach(); } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Override public void onResume() { super.onResume(); } @Override public void onPause() { super.onPause(); } @Override public void onDestroy() { super.onDestroy(); } private void setupMap() { GPSTrack gps = new GPSTrack(mContext); // Enable MyLocation layer of google map mMap.setMyLocationEnabled(true); Log.d(TAG, "MyLocation enabled"); // Set Map type mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL); // Grab current location **ERROR HERE/Returns Null** Location location = gps.getLocation(); Log.d(TAG, "Grabbing location..."); if (location != null) { Log.d(TAG, "location != null"); // Grab Latitude and Longitude double latitude = location.getLatitude(); double longitude = location.getLongitude(); Log.d(TAG, "Getting lat, long.."); // Initialize LatLng object LatLng latLng = new LatLng(latitude, longitude); Log.d(TAG, "LatLng initialized"); // Show current location on google map mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng)); // Zoom in on google map mMap.animateCamera(CameraUpdateFactory.zoomTo(20)); mMap.addMarker(new MarkerOptions().position( new LatLng(latitude, longitude)).title("You are here.")); } else { gps.showSettingsAlert(); } } } GPSTrack.java public class GPSTrack extends Service implements LocationListener{ private final Context mContext; private boolean isGPSEnabled = false; //See if network is connected to internet private boolean isNetworkEnabled = false; //See if you can grab the location private boolean canGetLocation = false; protected Location location = null; protected double latitude; protected double longitude; private static final long MINIMUM_DISTANCE_CHANGE_FOR_UPDATES = 10; //10 Meters private static final long MINIMUM_TIME_CHANGE_FOR_UPDATES = 1000 * 60 * 1; //1 minute protected LocationManager locationManager; public GPSTrack(Context context) { this.mContext = context; getLocation(); } public Location getLocation() { try { //Setup locationManager for controlling location services **ERROR HERE/Return Null** locationManager = (LocationManager) mContext.getSystemService(LOCATION_SERVICE); //See if GPS is enabled isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER); //See if Network is connected to the internet or carrier service isNetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER); if (!isGPSEnabled && !isNetworkEnabled) { Toast.makeText(getApplicationContext(), "No Network Provider Available", Toast.LENGTH_SHORT).show(); } else { this.canGetLocation = true; if (isNetworkEnabled) { locationManager.requestLocationUpdates( LocationManager.NETWORK_PROVIDER, MINIMUM_TIME_CHANGE_FOR_UPDATES, MINIMUM_DISTANCE_CHANGE_FOR_UPDATES, this); Log.d("GPS", "GPS Enabled"); if (locationManager != null) { location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER); if (location != null) { latitude = location.getLatitude(); longitude = location.getLongitude(); } } } } } catch (Exception e) { e.printStackTrace(); } return location; } public void stopUsingGPS() { if (locationManager != null) { locationManager.removeUpdates(GPSTrack.this); } } public double getLatitude() { if (location != null) { latitude = location.getLatitude(); } return latitude; } public double getLongitude() { if (location != null) { longitude = location.getLongitude(); } return longitude; } public boolean canGetLocation() { return this.canGetLocation; } public void showSettingsAlert() { AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext); //AlertDialog title alertDialog.setTitle("GPS Settings"); //AlertDialog message alertDialog.setMessage("GPS is not enabled. Do you want to go to Settings?"); alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub Intent i = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS); mContext.startActivity(i); } }); alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub dialog.cancel(); } }); alertDialog.show(); } @Override public void onLocationChanged(Location location) { // TODO Auto-generated method stub } @Override public void onStatusChanged(String provider, int status, Bundle extras) { // TODO Auto-generated method stub } @Override public void onProviderEnabled(String provider) { // TODO Auto-generated method stub } @Override public void onProviderDisabled(String provider) { // TODO Auto-generated method stub } @Override public IBinder onBind(Intent intent) { // TODO Auto-generated method stub return null; } } logcat 06-08 22:35:03.441: E/AndroidRuntime(1370): FATAL EXCEPTION: main 06-08 22:35:03.441: E/AndroidRuntime(1370): Process: com.google.android.gms, PID: 1370 06-08 22:35:03.441: E/AndroidRuntime(1370): java.lang.RuntimeException: Unable to start service com.google.android.gms.checkin.CheckinService@b1094e48 with Intent { cmp=com.google.android.gms/.checkin.CheckinService }: java.lang.SecurityException: attempting to read gservices without permission: Neither user 10053 nor current process has com.google.android.providers.gsf.permission.READ_GSERVICES. 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2719) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread.access$2100(ActivityThread.java:135) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.os.Handler.dispatchMessage(Handler.java:102) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.os.Looper.loop(Looper.java:136) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread.main(ActivityThread.java:5017) 06-08 22:35:03.441: E/AndroidRuntime(1370): at java.lang.reflect.Method.invokeNative(Native Method) 06-08 22:35:03.441: E/AndroidRuntime(1370): at java.lang.reflect.Method.invoke(Method.java:515) 06-08 22:35:03.441: E/AndroidRuntime(1370): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 06-08 22:35:03.441: E/AndroidRuntime(1370): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 06-08 22:35:03.441: E/AndroidRuntime(1370): at dalvik.system.NativeStart.main(Native Method) 06-08 22:35:03.441: E/AndroidRuntime(1370): Caused by: java.lang.SecurityException: attempting to read gservices without permission: Neither user 10053 nor current process has com.google.android.providers.gsf.permission.READ_GSERVICES. 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ContextImpl.enforce(ContextImpl.java:1685) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ContextImpl.enforceCallingOrSelfPermission(ContextImpl.java:1714) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.content.ContextWrapper.enforceCallingOrSelfPermission(ContextWrapper.java:572) 06-08 22:35:03.441: E/AndroidRuntime(1370): at imq.c(SourceFile:107) 06-08 22:35:03.441: E/AndroidRuntime(1370): at imq.a(SourceFile:121) 06-08 22:35:03.441: E/AndroidRuntime(1370): at imq.a(SourceFile:227) 06-08 22:35:03.441: E/AndroidRuntime(1370): at bwq.c(SourceFile:166) 06-08 22:35:03.441: E/AndroidRuntime(1370): at com.google.android.gms.checkin.CheckinService.a(SourceFile:237) 06-08 22:35:03.441: E/AndroidRuntime(1370): at com.google.android.gms.checkin.CheckinService.onStartCommand(SourceFile:211) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2702) AndroidManifest <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.app" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="14" android:targetSdkVersion="19" /> <uses-permission android:name="com.curio.permission.MAPS_RECEIVE" /> <uses-permission android:name="android.permission.CAMERA" /> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" /> <uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION" /> <uses-feature android:name="android.hardware.camera" android:required="true" /> <uses-feature android:glEsVersion="0x00020000" android:required="true" /> <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name="com.app.MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version" /> <meta-data android:name="com.google.android.maps.v2.API_KEY" android:value="AI........................" /> </application>

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• Multiple CodeSnippet in an XML .snippet file

  - by Frinavale

  I'm attempting to supplement the help features for my code by providing other developers with code snippets. These produce skeletons of code which demonstrate how to use/call my classes or methods. I've created a .snippet file and have placed it in the "%Visual Studio Folder%\Code Snippets\Visual Basic\My Snippets" folder. I've used the Code Snippets Manager and ensured that it included this folder so that I can access the snippets. Everything works well when I have 1 CodeSnippet tag within the root CodeSnippets tag.... When I add more than one CodeSnippet tag to the file (each with their own title, and their own code example) I'm experiencing something strange. The first CodeSnippet I've added contains code for adding something to my system, the second contains code for editing something in my system, and the third deleting something from the system. When I use the code snippet by right clicking and selecting "Insert Code Snippet", only the first code snippet in the file shows up as an option. When I select it, the code in the first CodeSnippet is inserted....but so is the code within the other CodeSnippet tags. Do you have to have a separate XML .snippet file for each code snippet you want to make available? After reading through MSDN about creating Code Snippets I was under the impression that this could all be done within one file. It seems that I'm not understanding something very basic here and would love to find the answer but apparently Code Snippets are under used so finding the answer has proven to be a little trickier than I first thought it would be. Thanks, -Frinny

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• Diff between <head id="Head1" runat="server"> and <asp:ContentPlaceHolder runat="server" ID="HeadCon

  - by justSteve

  Looking for an better understanding of how an mvc project should define javascript and css includes. I'm working with sample code where includes are defined like: <head id="Head1" runat="server"> <title><asp:ContentPlaceHolder ID="TitleContent" runat="server" />Affiliate Checkout</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <meta http-equiv="pragma" content="no-cache"> <script type="text/javascript" src="/Scripts/jquery.js"></script> <script type="text/javascript" src="/Scripts/jquery-ui-1.7.2.custom.min.js"></script> . . . <asp:ContentPlaceHolder runat="server" ID="HeadContent"></asp:ContentPlaceHolder> </head> I'm reading that to be that _all pages looking at this MasterPage will get jquery and jqueryUI and, additionally, each page will have the opportunity to add head elements thankx to the content placeholder HeadContent tag. The specific problem i'm troubleshooting is an instance where my rendered page is not including the 'prama no-cache' tag - as you see, it's defined in the upper level header section. Other .js and .css elements are making it into the rendered page so it very confusing to see that the no-cache tag isn't. When execute a 'View Generated Source' - the 'charset' is present the 'no-cache' is not.

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• How do I get google protocol buffer messages over a socket connection without disconnecting the clie

  - by Dan

  Hi there, I'm attempting to send a .proto message from an iPhone application to a Java server via a socket connection. However so far I'm running into an issue when it comes to the server receiving the data; it only seems to process it after the client connection has been terminated. This points to me that the data is getting sent, but the server is keeping its inputstream open and waiting for more data. Would anyone know how I might go about solving this? The current code (or at least the relevant parts) is as follows: iPhone: Person *person = [[[[Person builder] setId:1] setName:@"Bob"] build]; RequestWrapper *request = [[[RequestWrapper builder] setPerson:person] build]; NSData *data = [request data]; AsyncSocket *socket = [[AsyncSocket alloc] initWithDelegate:self]; if (![socket connectToHost:@"192.168.0.6" onPort:6666 error:nil]){ [self updateLabel:@"Problem connecting to socket!"]; } else { [self updateLabel:@"Sending data to server..."]; [socket writeData:data withTimeout:-1 tag:0]; [self updateLabel:@"Data sent, disconnecting"]; //[socket disconnect]; } Java: try { RequestWrapper wrapper = RequestWrapper.parseFrom(socket.getInputStream()); Person person = wrapper.getPerson(); if (person != null) { System.out.println("Persons name is " + person.getName()); socket.close(); } On running this, it seems to hang on the line where the RequestWrapper is processing the inputStream. I did try replacing the socket writedata method with [request writeToOutputStream:[socket getCFWriteStream]]; Which I thought might work, however I get an error claiming that the "Protocol message contained an invalid tag (zero)". I'm fairly certain that it doesn't contain an invalid tag as the message works when sending it via the writedata method. Any help on the matter would be greatly appreciated! Cheers! Dan (EDIT: I should mention, I am using the metasyntactic gpb code; and the cocoaasyncsocket implementation)

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• JQuery ajax request returns error and status 0

  - by Kucebe

  I use this pseudo-class to make ajax request to server: function RequestManager(url, params, success, error){ //save this ajax configuration this._ajaxCall = null; this._url= url; this._type = params.type; this._timer = params.timer || 0; this._success = function(){ alert("ok"); }; this._error = function(){ alert("ko"); }; } RequestManager.prototype = { require : function(tag){//here there will be a tag object in array format if(this.timer>0){ //wait this.timer } if(this.ajaxCall != null ){ this.ajaxCall.abort(); this.ajaxCall = null; } var self = this; this.ajaxCall = $.ajax({ url: this._url, type: this._type, data: tag, success: function(xmlResponse){ var responseArray = []; var response = _extractElements(xmlResponse, arrayResponse); self._success(response); }, error: self._error, complete : function(xhr, statusText){ alert(xhr.status); return null; } }); } When i instantiate a new object, and i use it to load a request, it always return to me error, and status code is 0. Server correctly generates an xml document. Why i can't get a correct 200 code back?

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• Clear form field after select for jQuery UI Autocomplete

  - by jonfhancock

  I'm developing a form, and using jQuery UI Autocomplete. When the user selects an option, I want the selection to pop into a span appended to the parent <p> tag. Then I want the field to clear rather than be populated with the selection. I have the span appearing just fine, but I can't get the field to clear. How do you cancel jQuery UI Autocomplete's default select action? Here is my code: var availableTags = ["cheese", "milk", "dairy", "meat", "vegetables", "fruit", "grains"]; $("[id^=item-tag-]").autocomplete({ source: availableTags, select: function(){ var newTag = $(this).val(); $(this).val(""); $(this).parent().append("<span>" + newTag + "<a href=\"#\">[x]</a> </span>"); } }); Simply doing $(this).val(""); doesn't work. What is maddening is that almost the exact function works fine if I ignore autocomplete, and just take action when the user types a comma as such: $('[id^=item-tag-]').keyup(function(e) { if(e.keyCode == 188) { var newTag = $(this).val().slice(0,-1); $(this).val(''); $(this).parent().append("<span>" + newTag + "<a href=\"#\">[x]</a> </span>"); } }); The real end result is to get autocomplete to work with multiple selections. If anybody has any suggestions for that, they would be welcome.

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• PHP preg_replace - Don't match with h1 tags

  - by James

  Hi there. I am using preg_replace to add a link to keywords if they are found within a long HTML string. I don't want to add a link if the keyword is found within h1 tags or strong tags. The below regex nearly works and basically says (I think): If the keyword is not immediately wrapped by either a h1 tag or a strong tag then replace with the keyword that was matched, as a bolded link to google. $result = preg_replace('%(?!<h1>)(?!<strong>)\b(bobs widgets)\b(?!<\/strong>)(?!<\/h1>)%i','<a href="http://www.google.com"><strong>$1</strong></a>', $result, -1); (the reason I don't want to match if in strong tags is because I am recursing through a lot of keywords so don't want to link an already linked keyword on subsequent passes) the above works fine and won't match: <h1>bobs widgets</h1> It will however match the keyword in the following text, because the h1 tag isn't immediately either side of the keyword: <h1>Here are bobs widgets for sale</h1> I need to make the spaces either side optional and have tried adding \s* but that doesn't get me anywhere. I'd be very grateful for a push in the right direction here.

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• Are Django template tags cached?

  - by thebossman

  I have gone through the (painful) process of writing a custom template tag for use in Django. It is registered as an inclusion_tag so that it renders a template. However, this tag breaks as soon as I try to change something. I've tried changing the number of parameters and correspondingly changing the parameters when it's called. It's clear the new tag code isn't being loaded, because an error is thrown stating that there is a mismatch in the number of parameters, and it's evident that it's attempting to call the old function. The same problem occurs if I try to change the name of the template being rendered and correspondingly change the name of the template on disk. It continues to try to call the old template. I've tried clearing old .pyc files with no luck. Overall, the system is acting as though it's caching the template tags, likely due to the register command. I have dug through endless threads trying to find out if this is so, but all could find it James Bennett stating here that register doesn't do anything. Please help!

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• jQuery, html5, append()/appendTo() and IE

  - by karbassi

  How to replicate: Create an html5 page. Make sure you have the script from remysharp.com/2009/01/07/html5-enabling-script/ added so that IE will notice the tags. Create an hardcoded <section id='anything'></section> tag. Using jQuery 1.3.2, append another section tag: $('#anything').append('<section id="whatever"></section>'); So far, everything works in all the browsers. Repeat the previous step. $('#whatever').append('<section id="fail"></section>'); This is where IE6/7 fails. Firefox/Safari will continue working. Error This is the error displayed. Thoughts It could be that IE6/7 can't handle the HTML5 section tag. I say this because when I change step 4 from <section> to <div>, IE6/7 will start working. If I use document.createElement() and create my new element, it works, but it seems like jQuery's append() has a problem with html5 elements.

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• Cannot install XML::LibXML module on Windows

  - by Deepak Konidena

  I am trying to use XPath to extract some HTML tags and data and for that I need to use XML::LibXML module. I tried installing it from CPAN shell but it doesn't install. I followed the instructions from CPAN site about the installation, that we need to install libxml2, iconv and zlib wrappers before installing XML::LibXML and it didn't work out. Also, if there is any other simpler module that gets my task done, please let me know. The task at hand: I am searching for a specific <dd> tag on a html page which is really big ( around 5000 - 10000) <dd> and <dt> tags. So, I am writing a script which matches the content within <dd> tag and fetches the content within the corresponding (next) <dt> tag. I wish i could i have been a little more clearer. Any help is greatly appreciated.

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