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• When NOT TO USE 'this' keyword?

  - by LifeH2O

  Sorry for asking it again, there are already 3 questions about this keyword. But all of them tell the purpose of 'this'. My question is when not to use 'this' keyword . OR Is it all right to use this keyword always in situation like the code class RssReader { private XmlTextReader _rssReader; private XmlDocument _rssDoc; private XmlNodeList _xn; protected XmlNodeList Item { get { return _xn; } } public int Count { get { return _count; } } public bool FetchFeed(String url) { this._rssReader = new XmlTextReader(url); this._rssDoc = new XmlDocument(); _rssDoc.Load(_rssReader); _xn = _rssDoc.SelectNodes("/rss/channel/item"); _count = _xn.Count; return true; } } here i have not used 'this' with "_xn" and "_count" also not with "_rssDoc.Load(_rssReader);" is it fine? Should i use "this" with all occurrences of class variables within the class?

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• An Interactive Console I/O Wrapper/Interceptor in C# - What is the issue?

  - by amazedsaint

  I was trying to put together an interactive Console interceptor/wrapper in C# over the weekend, by re-mixing few code samples I've found in SO and other sites. With what I've as of now, I'm unable to read back from the console reliably. Any quick pointers? public class ConsoleInterceptor { Process _interProc; public event Action<string> OutputReceivedEvent; public ConsoleInterceptor() { _interProc = new Process(); _interProc.StartInfo = new ProcessStartInfo("cmd"); InitializeInterpreter(); } public ConsoleInterceptor(string command) { _interProc = new Process(); _interProc.StartInfo = new ProcessStartInfo(command); InitializeInterpreter(); } public Process InterProc { get { return _interProc; } } private void InitializeInterpreter() { InterProc.StartInfo.RedirectStandardInput = true; InterProc.StartInfo.RedirectStandardOutput = true; InterProc.StartInfo.RedirectStandardError = true; InterProc.StartInfo.CreateNoWindow = true; InterProc.StartInfo.UseShellExecute = false; InterProc.StartInfo.WindowStyle = ProcessWindowStyle.Hidden; bool started = InterProc.Start(); Redirect(InterProc.StandardOutput); Redirect(InterProc.StandardError); } private void Redirect(StreamReader input) { new Thread((a) => { var buffer = new char[1]; while (true) { if (input.Read(buffer, 0, 1) > 0) OutputReceived(new string(buffer)); }; }).Start(); } private void OutputReceived(string text) { if (OutputReceivedEvent != null) OutputReceivedEvent(text); } public void Input(string input) { InterProc.StandardInput.WriteLine(input); InterProc.StandardInput.Flush(); } }

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• Accessing running task scheduled with java.util.Timer

  - by jbatista

  I'm working on a Java project where I have created a class that looks like this (abridged version): public class Daemon { private static Timer[] timerarray=null; private static Daemon instance=null; protected Daemon() { ArrayList<Timer> timers = new ArrayList<Timer>(); Timer t = new Timer("My application"); t.schedule(new Worker(), 10000,30000); timers.add(t); //... timerarray = timers.toArray(new Timer[]{}); } public static Daemon getInstance() { if(instance==null) instance=new Daemon(); return instance; } public SomeClass getSomeValueFromWorker() { return theValue; } ///////////////////////////////////////////// private class Worker extends TimerTask { public Worker() {} public void run() { // do some work } public SomeReturnClass someMethod(SomeType someParameter) { // return something; } } ///////////////////////////////////////////// } I start this class, e.g. by invoking daemon.getInstance();. However, I'd like to have some way to access the running task objects' methods (for example, for monitoring the objects' state). The Java class java.util.Timer does not seem to provide the means to access the running object, it just schedules the object instance extending TimerTask. Are there ways to access the "running" object instanciated within a Timer? Do I have to subclass the Timer class with the appropriate methods to somehow access the instance (this "feels" strange, somehow)? I suppose someone might have done this before ... where can I find examples of this "procedure"? Thank you in advance for your feedback.

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• Dynamcally resizing an open Accordion

  - by alavers

  I have an Accordion and the height of its content can be dynamically resized. I would like to see the Accordion dynamically respond to the child item's height, but I'm having trouble doing this. <lt:Accordion Name="MyAccordion" SelectionMode="ZeroOrOne" HorizontalAlignment="Stretch"> <lt:AccordionItem Name="MyAccordionItem" Header="MyAccordion" IsSelected="True" HorizontalContentAlignment="Stretch" VerticalAlignment="Stretch"> <StackPanel> <Button Content="Grow" Click="Grow"/> <Button Content="Shrink" Click="Shrink"/> <TextBox Name="GrowTextBox" Text="GrowTextBox" Height="400" Background="Green" SizeChanged="GrowTextBox_SizeChanged"/> </StackPanel> </lt:AccordionItem> </lt:Accordion> private void Grow(object sender, System.Windows.RoutedEventArgs e) { GrowTextBox.Height += 100; } private void Shrink(object sender, System.Windows.RoutedEventArgs e) { GrowTextBox.Height -= 100; } private void GrowTextBox_SizeChanged(object sender, System.Windows.SizeChangedEventArgs e) { MyAccordion.UpdateLayout(); MyAccordionItem.UpdateLayout(); } Mind you, if I collapse and then re-open the accordion, it takes shape just the way I want, but I'd like this resizing to occur immediately when the child resizes. I feebly attempted to fix this by adding a SizeChanged event handler that calls UpdateLayout() on the Accordion and AccordionItem, but this doesn't have any visual effect. I can't figure out where proper resizing takes place inside the Accordion control. Does anyone have an idea?

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• JPA - Entity design problem

  - by Yatendra Goel

  I am developing a Java Desktop Application and using JPA for persistence. I have a problem mentioned below: I have two entities: Country City Country has the following attribute: CountryName (PK) City has the following attribute: CityName Now as there can be two cities with same name in two different countries, the primaryKey for City table in the datbase is a composite primary key composed of CityName and CountryName. Now my question is How to implement the primary key of the City as an Entity in Java @Entity public class Country implements Serializable { private String countryName; @Id public String getCountryName() { return this.countryName; } } @Entity public class City implements Serializable { private CityPK cityPK; private Country country; @EmbeddedId public CityPK getCityPK() { return this.cityPK; } } @Embeddable public class CityPK implements Serializable { public String cityName; public String countryName; } Now as we know that the relationship from Country to City is OneToMany and to show this relationship in the above code, I have added a country variable in City class. But then we have duplicate data(countryName) stored in two places in the City class: one in the country object and other in the cityPK object. But on the other hand, both are necessary: countryName in cityPK object is necessary because we implement composite primary keys in this way. countryName in country object is necessary because it is the standard way of showing relashionship between objects. How to get around this problem?

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• nhibernate : Repository Session Management

  - by frosty

  At the moment my repository has 2 constructors. When i call these from my mvc website i am alway calling first constructor and thus opening a new session. Should i been passing in the session. How should i be doing this. public CompanyRepository() { _session = NHibernateHelper.OpenSession(); } public CompanyRepository(ISession session) { _session = session; } public class NHibernateHelper { private static ISessionFactory _sessionFactory; private static ISessionFactory SessionFactory { get { if (_sessionFactory == null) { var configuration = new Configuration(); configuration.Configure(); configuration.AddAssembly(typeof(UserProfile).Assembly); configuration.SetProperty(NHibernate.Cfg.Environment.ConnectionStringName, System.Environment.MachineName); _sessionFactory = configuration.BuildSessionFactory(); } return _sessionFactory; } } public static ISession OpenSession() { return SessionFactory.OpenSession(); } } I'm using the Ninject IOC container ( very new to me ). I have the following container. How would i bind the ISession to the CompanyRepository. private class EStoreDependencies : NinjectModule { public override void Load() { Bind<ICompanyRepository>().To<CompanyRepository>(); Bind<IUserProfileRepository>().To<UserProfileRepository>(); Bind<IAddressRepository>().To<AddressRepository>(); Bind<IRolesService>().To<AspNetRoleProviderWrapper>(); Bind<IUserService>().To<AspNetMembershipProviderWrapper>(); Bind<ICurrentUserSerivce>().To<DefaultCurrentUserSerivce>(); Bind<IPasswordService>().To<AspNetMembershipProviderWrapper>(); Bind<IStatusResponseRepository>().To<StatusResponseRepository>(); Bind<ICategoryRepository>().To<CategoryRepository>(); Bind<IProductRepository>().To<ProductRepository>(); } }

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• .net runtime type casting when using reflection

  - by Mike

  I have need to cast a generic list of a concrete type to a generic list of an interface that the concrete types implement. This interface list is a property on an object and I am assigning the value using reflection. I only know the value at runtime. Below is a simple code example of what I am trying to accomplish: public void EmployeeTest() { IList<Employee> initialStaff = new List<Employee> { new Employee("John Smith"), new Employee("Jane Doe") }; Company testCompany = new Company("Acme Inc"); //testCompany.Staff = initialStaff; PropertyInfo staffProperty = testCompany.GetType().GetProperty("Staff"); staffProperty.SetValue(testCompany, (staffProperty.PropertyType)initialStaff, null); } Classes are defined like so: public class Company { private string _name; public string Name { get { return _name; } set { _name = value; } } private IList<IEmployee> _staff; public IList<IEmployee> Staff { get { return _staff; } set { _staff = value; } } public Company(string name) { _name = name; } } public class Employee : IEmployee { private string _name; public string Name { get { return _name; } set { _name = value; } } public Employee(string name) { _name = name; } } public interface IEmployee { string Name { get; set; } } Any thoughts? I am using .NET 4.0. Would the new covariant or contravariant features help? Thanks in advance.

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• java.io.StreamCorruptedException: invalid stream header: 7371007E

  - by Alex

  Hello, this is pprobably a simple question . I got a client Server application which communicate using objects. when I send only one object from the client to server all works well. when I attempt to send several objects one after another on the same stream I get StreamCorruptedException. can some one direct me to the cause of this error . Thanks client write method private SecMessage[] send(SecMessage[] msgs) { SecMessage result[]=new SecMessage[msgs.length]; Socket s=null; ObjectOutputStream objOut =null; ObjectInputStream objIn=null; try { s=new Socket("localhost",12345); objOut=new ObjectOutputStream( s.getOutputStream()); for (SecMessage msg : msgs) { objOut.writeObject(msg); } objOut.flush(); objIn=new ObjectInputStream(s.getInputStream()); for (int i=0;i<result.length;i++) result[i]=(SecMessage)objIn.readObject(); } catch(java.io.IOException e) { alert(IO_ERROR_MSG+"\n"+e.getMessage()); } catch (ClassNotFoundException e) { alert(INTERNAL_ERROR+"\n"+e.getMessage()); } finally { try {objIn.close();} catch (IOException e) {} try {objOut.close();} catch (IOException e) {} } return result; } server read method //in is an inputStream Defined in the server SecMessage rcvdMsgObj; rcvdMsgObj=(SecMessage)new ObjectInputStream(in).readObject(); return rcvdMsgObj; and the SecMessage Class is public class SecMessage implements java.io.Serializable { private static final long serialVersionUID = 3940341617988134707L; private String cmd; //... nothing interesting here , just a bunch of fields , getter and setters }

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• Setting javascript prototype function within object class declaration

  - by Tauren

  Normally, I've seen prototype functions declared outside the class definition, like this: function Container(param) { this.member = param; } Container.prototype.stamp = function (string) { return this.member + string; } var container1 = new Container('A'); alert(container1.member); alert(container1.stamp('X')); This code produces two alerts with the values "A" and "AX". I'd like to define the prototype function INSIDE of the class definition. Is there anything wrong with doing something like this? function Container(param) { this.member = param; if (!Container.prototype.stamp) { Container.prototype.stamp = function() { return this.member + string; } } } I was trying this so that I could access a private variable in the class. But I've discovered that if my prototype function references a private var, the value of the private var is always the value that was used when the prototype function was INITIALLY created, not the value in the object instance: Container = function(param) { this.member = param; var privateVar = param; if (!Container.prototype.stamp) { Container.prototype.stamp = function(string) { return privateVar + this.member + string; } } } var container1 = new Container('A'); var container2 = new Container('B'); alert(container1.stamp('X')); alert(container2.stamp('X')); This code produces two alerts with the values "AAX" and "ABX". I was hoping the output would be "AAX" and "BBX". I'm curious why this doesn't work, and if there is some other pattern that I could use instead.

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• Using recursion to to trim a binary tree based on a given min and max value

  - by Justin

  As the title says, I have to trim a binary tree based on a given min and max value. Each node stores a value, and a left/right node. I may define private helper methods to solve this problem, but otherwise I may not call any other methods of the class nor create any data structures such as arrays, lists, etc. An example would look like this: overallRoot _____[50]____________________ / \ __________[38] _______________[90] / \ / _[14] [42] [54]_____ / \ \ [8] [20] [72] \ / \ [26] [61] [83] trim(52, 65); should return: overallRoot [54] \ [61] My attempted solution has three methods: public void trim(int min, int max) { rootFinder(overallRoot, min, max); } First recursive method finds the new root perfectly. private void rootFinder(IntTreeNode node, int min, int max) { if (node == null) return; if (overallRoot.data < min) { node = overallRoot = node.right; rootFinder(node, min, max); } else if (overallRoot.data > max) { node = overallRoot = node.left; rootFinder(node, min, max); } else cutter(overallRoot, min, max); } This second method should eliminate any further nodes not within the min/max, but it doesn't work as I would hope. private void cutter(IntTreeNode node, int min, int max) { if (node == null) return; if (node.data <= min) { node.left = null; } if (node.data >= max) { node.right = null; } if (node.data < min) { node = node.right; } if (node.data > max) { node = node.left; } cutter(node.left, min, max); cutter(node.right, min, max); } This returns: overallRoot [54]_____ \ [72] / [61] Any help is appreciated. Feel free to ask for further explanation as needed.

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• java.lang.OutOfMemoryError: bitmap size exceeds VM budget

  - by Angel

  Hi, I am trying to change the layout of my application from portrait to landscape and vice-versa. But if i do it frequently or more than once then at times my application crashes.. Below is the error log. Please suggest what can be done? < 01-06 09:52:27.787: ERROR/dalvikvm-heap(17473): 1550532-byte external allocation too large for this process. 01-06 09:52:27.787: ERROR/dalvikvm(17473): Out of memory: Heap Size=6471KB, Allocated=4075KB, Bitmap Size=9564KB 01-06 09:52:27.787: ERROR/(17473): VM won't let us allocate 1550532 bytes 01-06 09:52:27.798: DEBUG/skia(17473): --- decoder-decode returned false 01-06 09:52:27.798: DEBUG/AndroidRuntime(17473): Shutting down VM 01-06 09:52:27.798: WARN/dalvikvm(17473): threadid=3: thread exiting with uncaught exception (group=0x4001e390) 01-06 09:52:27.807: ERROR/AndroidRuntime(17473): Uncaught handler: thread main exiting due to uncaught exception 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): java.lang.RuntimeException: Unable to start activity ComponentInfo{}: android.view.InflateException: Binary XML file line #2: Error inflating class 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2596) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2621) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3812) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.ActivityThread.access$2300(ActivityThread.java:126) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1936) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.os.Handler.dispatchMessage(Handler.java:99) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.os.Looper.loop(Looper.java:123) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.ActivityThread.main(ActivityThread.java:4595) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at java.lang.reflect.Method.invokeNative(Native Method) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at java.lang.reflect.Method.invoke(Method.java:521) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at dalvik.system.NativeStart.main(Native Method) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): Caused by: android.view.InflateException: Binary XML file line #2: Error inflating class 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.LayoutInflater.createView(LayoutInflater.java:513) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at com.android.internal.policy.impl.PhoneLayoutInflater.onCreateView(PhoneLayoutInflater.java:56) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:563) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.LayoutInflater.inflate(LayoutInflater.java:385) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.LayoutInflater.inflate(LayoutInflater.java:320) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.LayoutInflater.inflate(LayoutInflater.java:276) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:207) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.Activity.setContentView(Activity.java:1629) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at onCreate(Game.java:98) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2544) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): ... 12 more 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): Caused by: java.lang.reflect.InvocationTargetException 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.widget.LinearLayout.(LinearLayout.java:92) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at java.lang.reflect.Constructor.constructNative(Native Method) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at java.lang.reflect.Constructor.newInstance(Constructor.java:446) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.LayoutInflater.createView(LayoutInflater.java:500) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): ... 22 more 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): Caused by: java.lang.OutOfMemoryError: bitmap size exceeds VM budget 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.graphics.BitmapFactory.nativeDecodeAsset(Native Method) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.graphics.BitmapFactory.decodeStream(BitmapFactory.java:464) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.graphics.BitmapFactory.decodeResourceStream(BitmapFactory.java:340) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.graphics.drawable.Drawable.createFromResourceStream(Drawable.java:697) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.content.res.Resources.loadDrawable(Resources.java:1705) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.content.res.TypedArray.getDrawable(TypedArray.java:548) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.View.(View.java:1850) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.View.(View.java:1799) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): at android.view.ViewGroup.(ViewGroup.java:296) 01-06 09:52:27.857: ERROR/AndroidRuntime(17473): ... 26 more

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• Java Binary Tree. Priting InOrder traversal

  - by user69514

  I am having some problems printing an inOrder traversal of my binary tree. Even after inserting many items into the tree it's only printing 3 items. public class BinaryTree { private TreeNode root; private int size; public BinaryTree(){ this.size = 0; } public boolean insert(TreeNode node){ if( root == null) root = node; else{ TreeNode parent = null; TreeNode current = root; while( current != null){ if( node.getData().getValue().compareTo(current.getData().getValue()) <0){ parent = current; current = current.getLeft(); } else if( node.getData().getValue().compareTo(current.getData().getValue()) >0){ parent = current; current = current.getRight(); } else return false; if(node.getData().getValue().compareTo(parent.getData().getValue()) < 0) parent.setLeft(node); else parent.setRight(node); } } size++; return true; } /** * */ public void inOrder(){ inOrder(root); } private void inOrder(TreeNode root){ if( root.getLeft() !=null) this.inOrder(root.getLeft()); System.out.println(root.getData().getValue()); if( root.getRight() != null) this.inOrder(root.getRight()); } }

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• Why is the this-pointer needed to access inherited attributes?

  - by Shadow

  Hi, assume the following class is given: class Base{ public: Base() {} Base( const Base& b) : base_attr(b.base_attr) {} void someBaseFunction() { .... } protected: SomeType base_attr; }; When I want a class to inherit from this one and include a new attribute for the derived class, I would write: class Derived: public Base { public: Derived() {} Derived( const Derived& d ) : derived_attr(d.derived_attr) { this->base_attr = d.base_attr; } void SomeDerivedFunction() { .... } private: SomeOtherType derived_attr; }; This works for me (let's ignore eventually missing semicolons or such please). However, when I remove the "this-" in the copy constructor of the derived class, the compiler complains that "'base_attr' was not declared in this scope". I thought that, when inheriting from a class, the protected attributes would then also be accessible directly. I did not know that the "this-" pointer was needed. I am now confused if it is actually correct what I am doing there, especially the copy-constructor of the Derived-class. Because each Derived object is supposed to have a base_attr and a derived_attr and they obviously need to be initialized/set correctly. And because Derived is inheriting from Base, I don't want to explicitly include an attribute named "base_attr" in the Derived-class. IMHO doing so would generally destroy the idea behind inheritance, as everything would have to be defined again. EDIT Thank you all for the quick answers. I completely forgot the fact that the classes actually are templates. Please, see the new examples below, which are actually compiling when including "this-" and are failing when omiting "this-" in the copy-constructor of the Derived-class: Base-class: #include <iostream> template<class T> class Base{ public: Base() : base_attr(0) {} Base( const Base& b) : base_attr(b.base_attr) {} void baseIncrement() { ++base_attr; } void printAttr() { std::cout << "Base Attribute: " << base_attr << std::endl; } protected: T base_attr; }; Derived-class: #include "base.hpp" template< class T > class Derived: public Base<T>{ public: Derived() : derived_attr(1) {} Derived( const Derived& d) : derived_attr(d.derived_attr) { this->base_attr = d.base_attr; } void derivedIncrement() { ++derived_attr; } protected: T derived_attr; }; and for completeness also the main function: #include "derived.hpp" int main() { Derived<int> d; d.printAttr(); d.baseIncrement(); d.printAttr(); Derived<int> d2(d); d2.printAttr(); return 0; }; I am using g++-4.3.4. Although I understood now that it seems to come from the fact that I use template-class definitions, I did not quite understand what is causing the problem when using templates and why it works when not using templates. Could someone please further clarify this?

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• BackgroundWorker and foreach loop

  - by tomfox66

  I have to process a loop with backgroundworkers. Before I start a new loop iteration I need to wait until the provious backgroundworker has finished. A while loop inside my foreach loop with isbusy flag doesn's seem like a good idea to me. How should I design this loop so it waits for the bg-worker to end before iterating the loop public void AutoConnect() { string[] HardwareList = new string[] { "d1", "d4", "ds1_2", "ds4_2" }; foreach (string HW in HardwareList) { if (backgroundWorker1.IsBusy != true) { backgroundWorker1.RunWorkerAsync(HW); // Wait here until backgroundWorker1 finished } } } private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) { BackgroundWorker worker = sender as BackgroundWorker; string FileName = e.Argument as string; try { if ((worker.CancellationPending == true)) { e.Cancel = true; } else { // Time consuming operation ParseFile(Filename); } } catch { } } private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e) { label1.Text = e.ProgressPercentage.ToString() + " lines"; } private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { if(e.Cancelled == true) { //this.tbProgress.Text = "Canceled!"; } else if(!(e.Error == null)) { //this.tbProgress.Text = ("Error: " + e.Error.Message); } else { label1.text = "Done!"; } }

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• C# - Take Screenshot based on a Timer

  - by APShredder

  Hello everybody. I'm trying to create a WinForms app that takes a screenshot on a set interval. I think my code is correct, but when I try to run it, I get the error message "System.Runtime.InteropServices.ExternalException was unhandled, A generic error occurred in GDI+." System.Windows.Forms.Timer t = new System.Windows.Forms.Timer(); Thread th; private static Bitmap bmpScreenshot; private static Graphics gfxScreenshot; void TakeScreenShot() { bmpScreenshot = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height, PixelFormat.Format32bppArgb); gfxScreenshot = Graphics.FromImage(bmpScreenshot); gfxScreenshot.CopyFromScreen(Screen.PrimaryScreen.Bounds.X, Screen.PrimaryScreen.Bounds.Y, 0, 0, Screen.PrimaryScreen.Bounds.Size, CopyPixelOperation.SourceCopy); bmpScreenshot.Save(Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory) + @"\ScreenCaptures", ImageFormat.Png); th.Abort(); } void StartThread(object sender, EventArgs e) { th = new Thread(new ThreadStart(TakeScreenShot)); th.Start(); } private void Form1_Load(object sender, EventArgs e) { Directory.CreateDirectory(Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory) + @"\ScreenCaptures"); t.Interval = 500; t.Tick += new EventHandler(StartThread); t.Start(); } The line that's giving my trouble is: bmpScreenshot.Save(Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory) + @"\ScreenCaptures", ImageFormat.Png); Any ideas about what is going wrong? Thanks in advance.

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• Auto-implemented getters and setters vs. public fields

  - by tclem

  I see a lot of example code for C# classes that does this: public class Point { public int x { get; set; } public int y { get; set; } } Or, in older code, the same with an explicit private backing value and without the new auto-implemented properties: public class Point { private int _x; private int _y; public int x { get { return _x; } set { _x = value; } } public int y { get { return _y; } set { _y = value; } } } My question is why. Is there any functional difference between doing the above and just making these members public fields, like below? public class Point { public int x; public int y; } To be clear, I understand the value of getters and setters when you need to do some translation of the underlying data. But in cases where you're just passing the values through, it seems needlessly verbose.

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• Cross-thread operation not valid: accessed from a thread other than the thread it was created on.

  - by user307524

  Hi, I want to remove checked items from checklistbox (winform control) in class file method which i am calling asynchronously using deletegate. but it showing me this error message:- Cross-thread operation not valid: Control 'checkedListBox1' accessed from a thread other than the thread it was created on. i have tried invoke required but again got the same error. Sample code is below: private void button1_Click(object sender, EventArgs e) { // Create an instance of the test class. Class1 ad = new Class1(); // Create the delegate. AsyncMethodCaller1 caller = new AsyncMethodCaller1(ad.TestMethod1); //callback delegate IAsyncResult result = caller.BeginInvoke(checkedListBox1, new AsyncCallback(CallbackMethod)," "); } In class file code for TestMethod1 is : - private delegate void dlgInvoke(CheckedListBox c, Int32 str); private void Invoke(CheckedListBox c, Int32 str) { if (c.InvokeRequired) { c.Invoke(new dlgInvoke(Invoke), c, str); c.Items.RemoveAt(str); } else { c.Text = ""; } } // The method to be executed asynchronously. public string TestMethod1(CheckedListBox chklist) { for (int i = 0; i < 10; i++) { string chkValue = chklist.CheckedItems[i].ToString(); //do some other database operation based on checked items. Int32 index = chklist.FindString(chkValue); Invoke(chklist, index); } return ""; }

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• Are there any guarantees in JLS about order of execution static initialization blocks?

  - by Roman

  I wonder if it's reliable to use a construction like: private static final Map<String, String> engMessages; private static final Map<String, String> rusMessages; static { engMessages = new HashMap<String, String> () {{ put ("msgname", "value"); }}; rusMessages = new HashMap<String, String> () {{ put ("msgname", "????????"); }}; } private static Map<String, String> msgSource; static { msgSource = engMessages; } public static String msg (String msgName) { return msgSource.get (msgName); } Is there a possibility that I'll get NullPointerException because msgSource initialization block will be executed before the block which initializes engMessages? (about why don't I do msgSource initialization at the end of upper init. block: just the matter of taste; I'll do so if the described construction is unreliable)

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• ProtoInclude for fields ?

  - by Big

  I have a simple object [ProtoContract] public class DataChangedEventArgs<T> : EventArgs { private readonly object key; private readonly T data; private readonly DataChangeType changeType; ///<summary> /// Key to identify the data item ///</summary> public object Key { get { return key; } } [ProtoMember(2, IsRequired = true)] public T Data { get { return data; } } [ProtoMember(3, IsRequired = true)] public DataChangeType ChangeType { get { return changeType; } } and I have a problem with the key. Its type is object, but it can be either int, long or string. I would intuitively use a ProtoInclude attribute to say "expect these types" but unfortunately they are class only attribute. Does anybody has any idea how I could work around this ? For background, the public object Key is here for historical reasons (and all over the place) so I would very much like to avoid the mother of all refactorings ;-) Any chance I could get this to Serialize, even force it to Serialize as a string ?

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• zend session exception on zend_session::start with forms

  - by Grant Collins

  Hi I'm having issues with trying to use Zend_Form_SubForm and sessions. My controller is in essance acting a wizard showing different subforms depending on the stage of the wizard. Using the example I am planning on storing the forms in a session namespace. My controller looks like this. include 'mylib/Form/addTaskWizardForm.php'; class AddtaskController extends Zend_Controller_Action{ private $config = null; private $log = null; private $subFormSession = null; /** * This function is called and initialises the global variables to this object * which is the configuration details and the logger to write to the log file. */ public function init(){ $this->config = Zend_Registry::getInstance()->get('config'); $this->log = Zend_Registry::getInstance()->get('log'); //set layout $this->_helper->layout->setLayout('no-sidemenus'); //we need to get the subforms and $wizardForms = new addTaskWizardForm(); $this->subFormSession = new Zend_Session_Namespace('addTaskWizardForms'); if(!isset($this->subFormSession->subforms)){ $this->subFormSession->subforms = $wizardForms; } } /** * The Landing page controller for the site. */ public function indexAction(){ $form = $this->subFormSession->subforms->getSubForm('start'); $this->view->form = $form; } However this is causing the application session to crash out with Uncaught exception 'Zend_Session_Exception' with message 'Zend_Session::start() Any idea why this is having issues with the Zend Session?? thanks.

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• NullPointerException with static variables

  - by tomekK

  I just hit very strange (to me) behaviour of java. I have following classes: public abstract class Unit { public static final Unit KM = KMUnit.INSTANCE; public static final Unit METERS = MeterUnit.INSTANCE; protected Unit() { } public abstract double getValueInUnit(double value, Unit unit); protected abstract double getValueInMeters(double value); } And: public class KMUnit extends Unit { public static final Unit INSTANCE = new KMUnit(); private KMUnit() { } //here are abstract methods overriden } public class MeterUnit extends Unit { public static final Unit INSTANCE = new MeterUnit(); private MeterUnit() { } ///abstract methods overriden } And my test case: public class TestMetricUnits extends TestCase { @Test public void testConversion() { System.out.println("Unit.METERS: " + Unit.METERS); System.out.println("Unit.KM: " + Unit.KM); double meters = Unit.KM.getValueInUnit(102.11, Unit.METERS); assertEquals(0.10211, meters, 0.00001); } } 1) MKUnit and MeterUnit are both singletons initialized statically, so during class loading. Constructors are private, so they can't be initialized anywhere else. 2) Unit class contains static final references to MKUnit.INSTANCE and MeterUnit.INSTANCE I would expect that: KMUnit class is loaded and instance is created. MeterUnit class is loaded and instance is created. Unit class is loaded and both KM and METERS variable are initialized, they are final so they cant be changed. But when I run my test case in console with maven my result is: T E S T S Running de.audi.echargingstations.tests.TestMetricUnits Unit.METERS: m Unit.KM: null Tests run: 3, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.089 sec <<< FAILURE! - in de.audi.echargingstations.tests.TestMetricUnits testConversion(de.audi.echargingstations.tests.TestMetricUnits) Time elapsed: 0.011 sec <<< ERROR! java.lang.NullPointerException: null at de.audi.echargingstations.tests.TestMetricUnits.testConversion(TestMetricUnits.java:29) Results : Tests in error: TestMetricUnits.testConversion:29 NullPointer And the funny part is that, when I run this test from eclipse via JUnit runner everything is fine, I have no NullPointerException and in console I have: Unit.METERS: m Unit.KM: km So the question is: what can be the reason that KM variable in Unit is null (and in the same time METERS is not null)

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• Creating a blocking Queue<T> in .NET?

  - by spoon16

  I have a scenario where I have multiple threads adding to a queue and multiple threads reading from the same queue. If the queue reaches a specific size all threads that are filling the queue will be blocked on add until an item is removed from the queue. The solution below is what I am using right now and my question is: How can this be improved? Is there an object that already enables this behavior in the BCL that I should be using? internal class BlockingCollection<T> : CollectionBase, IEnumerable { //todo: might be worth changing this into a proper QUEUE private AutoResetEvent _FullEvent = new AutoResetEvent(false); internal T this[int i] { get { return (T) List[i]; } } private int _MaxSize; internal int MaxSize { get { return _MaxSize; } set { _MaxSize = value; checkSize(); } } internal BlockingCollection(int maxSize) { MaxSize = maxSize; } internal void Add(T item) { Trace.WriteLine(string.Format("BlockingCollection add waiting: {0}", Thread.CurrentThread.ManagedThreadId)); _FullEvent.WaitOne(); List.Add(item); Trace.WriteLine(string.Format("BlockingCollection item added: {0}", Thread.CurrentThread.ManagedThreadId)); checkSize(); } internal void Remove(T item) { lock (List) { List.Remove(item); } Trace.WriteLine(string.Format("BlockingCollection item removed: {0}", Thread.CurrentThread.ManagedThreadId)); } protected override void OnRemoveComplete(int index, object value) { checkSize(); base.OnRemoveComplete(index, value); } internal new IEnumerator GetEnumerator() { return List.GetEnumerator(); } private void checkSize() { if (Count < MaxSize) { Trace.WriteLine(string.Format("BlockingCollection FullEvent set: {0}", Thread.CurrentThread.ManagedThreadId)); _FullEvent.Set(); } else { Trace.WriteLine(string.Format("BlockingCollection FullEvent reset: {0}", Thread.CurrentThread.ManagedThreadId)); _FullEvent.Reset(); } } }

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• Java Concurrency in practice sample question

  - by andy boot

  I am reading "Java Concurrency in practice" and looking at the example code on page 51. According to the book this piece of code is at risk of of failure if it has not been published properly. Because I like to code examples and break them to prove how they work. I have tried to make it throw an AssertionError but have failed. (Leading me to my previous question) Can anyone post sample code so that an AssertionError is thrown? Rule: Do not modify the Holder class. public class Holder{ private int n; public Holder(int n){ this.n = n; } public void assertSanity(){ if (n != n) { throw new AssertionError("This statement is false"); } } } I have modified the class to make it more fragile but I still can not get an AssertionError thrown. class Holder2{ private int n; private int n2; public Holder2(int n) throws InterruptedException{ this.n = n; Thread.sleep(200); this.n2 = n; } public void assertSanity(){ if (n != n2) { throw new AssertionError("This statement is false"); } } } Is it possible to make either of the above classes throw an AssertionError? Or do we have to accept that they may occasionally do so and we can't write code to prove it?

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• How to combine multiple uiBinder-based widgets?

  - by jprusakova

  I need to insert a [number of] uiBinder-based widgets into another one, at a particular spot. The inserted widget has a somewhat complicated layout, so I am trying to define it in HTML. referencePanel.add(...) fails with NoSuchElement exception. reference.getElement().toSource returns "undefined". Any suggestions on how to do that? public class AppUIDemo extends Composite { @UiTemplate("AppUIDemo.ui.xml") interface AppUIDemoUiBinder extends UiBinder<Widget, AppUIDemo> { } @UiTemplate("ReferenceUI.ui.xml") interface ReferenceUIUiBinder extends UiBinder<Widget, ReferenceUI> { } private static AppUIDemoUiBinder uiBinder = GWT .create(AppUIDemoUiBinder.class); private static ReferenceUIUiBinder refUIBinder = GWT .create(ReferenceUIUiBinder.class); @UiField HTMLPanel referencePanel; public AppUIDemo() { initWidget(uiBinder.createAndBindUi(this)); ReferenceUI reference = new ReferenceUI(refUIBinder); referencePanel.add(reference, reference.getElement().getId()); } } public class ReferenceUI extends Composite { interface ReferenceUIUiBinder extends UiBinder<Widget,ReferenceUI> { } private static ReferenceUIUiBinder uiBinder = GWT .create(ReferenceUIUiBinder.class); public ReferenceUI() { initWidget(uiBinder.createAndBindUi(this)); } public CreditReferenceUI(final UiBinder<Widget, CreditReferenceUI> binder) { initWidget(binder.createAndBindUi(this)); } }

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• Struts2 Converting Enum Array fills array with single null value

  - by Kyle Partridge

  For a simple action class with these member variables: ... private TestConverterEnum test; private TestConverterEnum[] tests; private List<TestConverterEnum> tList; ... And a simple enum: public enum TestConverterEnum { A, B, C; } Using the default struts2 enum conversion, when I send the request like so: TestConterter.action?test=&tests=&tList=&b=asdf For test I get a null value, which is expected. For the Array and List, however, I get and Array (or list) with one null element. Is this what is expected? Is there a way to prevent this. We recently upgraded our struts2 version, and we had our own converters, which also don't work in this case, so I was hoping to use the default conversion method. We already have code that is validating these arrays for null and length, and I don't want to have to add another condition to these branches. Is there a way to prevent this bevavior?

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