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• Resources and techniques/methods for SCJP preparation ?

  - by BenoitParis

  I am passing the SCJP 6 exam in a month. I have the "SCJP Sun Certified Programmer for Java 6 Exam 310-065" book. It seems great for the exam. But I want your advice on this. Getting the closest possible to 100% would be great. I have found a site that answered some of the questions you ask yourself when you go trough the book. Here is it : http://www.janeg.ca/java2.html As you can see it was written for Java 2 :/ I have written another specific question here on StackOverflow about the usefulness of JVM specification and Java compiler code for the SCJP. Will Update the results here. Here it is. Please share the resources you used in preparing the exam. Please also specify any resources that you think might help. Any type of resource is welcome: books, code, specs, sites, wikies, papers, online tests, grandmas... Please also share on any method/technique that helped you prepare the exam. Please also comment on the return you got from the resource and the method (for the learning process and for points in the exam) I'll begin: Book : "SCJP Sun Certified Programmer for Java 6 Exam 310-065". Seems like the official book for the preparation. Technique : Writing code in a text editor and compiling it with javac to test a question. NO IDEs! It helps you get a a straight answer to a question you have. It helps you pay attention to every word in the code (and this is very important in the SCJP) EDIT: Added dimension: Are there good, up-to-date online tests?

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• Thread loses Message after wait() and notify()

  - by fugu2.0

  Hey Guys! I have a problem handling messages in a Thread. My run-method looks like this public void run() { Looper.prepareLooper(); parserHandler = new Handler { public void handleMessage(Message msg) { Log.i("","id from message: "+msg.getData.getString("id")); // handle message this.wait(); } } } I have several Activities sending messages to this thread, like this: Message parserMessage = new Message(); Bundle data = new Bundle(); data.putString("id", realId); data.putString("callingClass", "CategoryList"); parserMessage.setData(data); parserMessage.what = PARSE_CATEGORIES_OR_PRODUCTS; parserHandler = parser.getParserHandler(); synchronized (parserHandler) { parserHandler.notify(); Log.i("","message ID: " + parserMessage.getData().getString("id")); } parserHandler.sendMessage(parserMessage); The problem is that the run-method logs "id from message: null" though "message ID" has a value in the Log-statement. Why does the message "lose" it's data when being send to the thread? Has it something to do with the notify? Thanks for your help

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• Finding a list of indices from master array using secondary array with non-unique entries

  - by fideli

  I have a master array of length n of id numbers that apply to other analogous arrays with corresponding data for elements in my simulation that belong to those id numbers (e.g. data[id]). Were I to generate a list of id numbers of length m separately and need the information in the data array for those ids, what is the best method of getting a list of indices idx of the original array of ids in order to extract data[idx]? That is, given: a=numpy.array([1,3,4,5,6]) # master array b=numpy.array([3,4,3,6,4,1,5]) # secondary array I would like to generate idx=numpy.array([1,2,1,4,2,0,3]) The array a is typically in sequential order but it's not a requirement. Also, array b will most definitely have repeats and will not be in any order. My current method of doing this is: idx=numpy.array([numpy.where(a==bi)[0][0] for bi in b]) I timed it using the following test: a=(numpy.random.uniform(100,size=100)).astype('int') b=numpy.repeat(a,100) timeit method1(a,b) 10 loops, best of 3: 53.1 ms per loop Is there a better way of doing this?

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• testng multiple suites

  - by Eli

  Hi people. my problem is as follows: i am testing a web-ui using selenium and testng. i have a test suite with many test classes in it. i have a method with the @BeforeSuite witch also has a @Parameters annotation, this method recieves as a parameter the browser in witch the selenium will test by run,executing the lines: selenium = new DefaultSelenium("localhost", 4444, **browser**, "http://localhost:8099"); selenium.start(); the xml im using to run the test suite is: <suite name="suite"> <parameter name = "browser" value = "*firefox"/> <test name="allTests"> <classes> <class name="test.webui.MemcachedDeploymentTest" /> </classes> </test> </suite> this works fine and the test runs in firefox. my problem is that i would like to somehow run this suite again, immediatly after the first run finishes, but this time with chrome as the browser. i now have 2 xml suites, one with chrome and one with firefox, is there any way to run these test suites one after the other automatically? maybe using a third xml? Thanks in advance

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• Avoiding mass propagation of properties and events for exposure to ViewModels.

  - by firoso

  I have an MVVM application I am developing that is to the point where I'm ready to start putting together a user interface (my client code is largely functional) I'm now running into the issue that I'm trying to get my application data to where I need it so that it can be consumed by the view model and then bound to the view. Unfortunately, it seems that I've either got a few structural oversights, or I'm just going to have to face the reality that I need to be propogating events and raising excessive amounts of errors to notify view models that thier properties have changed. Let me go into some examples of my issue: I have a class "Unit" contained in a class "Test", contained in a class "Session" contained in a class "TestManager" which is contained in "TestDataModel" which is utilized by "TestViewModel" which is databound to by my "TestView" .... WHOA. Now, consider that Unit (the bottom of the heiarchy) has a property called "Results" that is updated periodically, I want to expose that to my viewmodel and then databind it to my view, trouble is, the only way I can really think to do this is to perpetuate events WAY up a chain that say "I've been updated!" and then request the new value... This seems like an aweful way to do this. Alternatively, I could register a static event and raise it, and have the appropriate "Unit view model" grab the event and request the update. This SEEMS better... but... static events? Is that a taboo idea? Also, having an expression like: TestDataModel.TestManager.Session.Test.Unit.Results[i] Seems REALLY gross to have on a View Model. I know this all reeks of a bad design issue, but I can't figure out what I did wrong? Should I be using more singleton/container controlled lifetimes type objects? Register object instances with static helper containers? Obviously these are hard questions to answer without being intimate with the existing structure, but if you've run into situations like this, what did you do to refactor? Should I just live with this, add mass events, and propogate them?

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• Javascript not registering/executing after button click

  - by rs

  I have a textbox which i convert to tinymce textbox using tinymce.js file. I'm trying to add a new script with database fields substituted based on selection made from dropdownlist to page using registerstartupscript. In page load protected sub page_load(byVal sender as object, byval e as EventArgs) handles me.load AddScriptToPage() if not page.ispostback() then session("fname") = nothing end if end sub Script Method Sub AddScriptToPage() dim _script = " c.onRenderMenu.add(function(c, m) { " & _ add_columns() & _ "}); " ClientScript.RegisterStartupScript(Me.GetType(), keyword,_script) End Sub function add_columns() as string dim ret_string = String.empty select case ddlList.selectedvalue case 1 sqlcommand = "xyz" case 2 sqlcommand = "xyz" case 3 //Load from excel sqlcommand = nothing end select if sqlcommand isnot nothing then executereader() while reader.read() ret_string = ret_string & reader("column") end while elseif session("fname") isnot nothing dt = getdatatable(session("fname").tostring()) //method that opens oledb connection and returns columns for each dr in dt.rows ret_string = ret_string & dr("column") next end if add_columns = ret_string end function When excel file is uploaded to server this event is called protected sub btnclick(byVal sender as object, byval e as EventArgs) if hasfile then 'i have custom properties set after control validation 'Upload file 'set session value with filepath session("fname") = filepath 'call js register event AddScriptToPage() end if end sub When i click upload button i'm calling AddScriptToPage, and debug it it hits AddScripttoPage event and executes it but it doesn't showup on page. It should show column names in tinymce editor but it doesn't. But when i click another button on the same page it shows (becos session has the filename). On Upload button click page flow: Page load - AddScriptToPage is executed (registers scripts with no columns) Then AddScriptToPage in btnclick event is executed (registers scripts with columns) Why is this script not getting registered even though it is executed on vb code on uploadclick event? And why does it show up after another button click and not original button click that calls this event?

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• Getting the last User ID in Zend Framework

  - by Ryan Murphy

  Using MySQL query browser, I manually made a table called users and input some date in the fields. I set the primary key to id and set it to auto increment. There are 3 rows, the highest id is 3. I then made the following class in the method directory to call upon the data in the table etc. class Application_Model_DbTable_User extends Zend_Db_Table_Abstract { protected $_name = 'user'; public function getLatestUserId() { $id = $this->getAdapter()->lastInsertId(); return $id; } } In the controller I do the following which gets the value generated by the method and lets the view access it: $usersDbModel = new Application_Model_DbTable_User(); $lastUserId = $usersDbModel->getLatestUserId(); $this->view->lastUserId = $lastUserId; In the view I then echo it to display it to the user: echo $this->lastUserId; However, even though my last id in the users table is 3. It displays 0. I have also tried: public function getLatestUserId() { $sql = 'SELECT max(id) FROM user'; $query = $this->query($sql); $result = $query->fetchAll(); return $result; } But this just throws out a server error. What have I done wrong? Am I missing something? Is there another way of doing this?

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• What is the simplest way to implement multithreading in c# to existing code

  - by Kaeso

  I have already implemented a functionnal application that parses 26 pages of html all at once to produce an xml file with data contained on the web pages. I would need to implement a thread so that this method can work in the background without causing my app to seems unresponsive. Secondly, I have another function that is decoupled from the first one which compares two xml files to produce a third one and then transform this third xml file to produce an html page using XSLT. This would have to be on a thread, where I can click Cancel to stop the thread whithout crashing the app. What is the easiest best way to do this using WPF forms in VS 2010 ? I have chosen to use the BackgroundWorker. BackgroundWorker implementation: public partial class MainWindow : Window { private BackgroundWorker bw = new BackgroundWorker(); public MainWindow() { InitializeComponent(); bw.WorkerReportsProgress = true; bw.DoWork += new DoWorkEventHandler(bw_DoWork); bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted); } private void Window_Loaded(object sender, RoutedEventArgs e) { this.LoadFiles(); } private void btnCompare_Click(object sender, EventArgs e) { if (bw.IsBusy != true) { progressBar2.IsIndeterminate = true; // Start the asynchronous operation. bw.RunWorkerAsync(); } } private void bw_DoWork(object sender, DoWorkEventArgs e) { StatsProcessor proc = new StatsProcessor(); if (lstStatsBox1.SelectedItem != null) if (lstStatsBox2.SelectedItem != null) proc.CompareStats(lstStatsBox1.SelectedItem.ToString(), lstStatsBox2.SelectedItem.ToString()); } private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { progressBar2.IsIndeterminate = false; progressBar2.Value = 100; } I have started with the bgworker solution, but it seems that the bw_DoWork method is never called when btnCompare is clicked, I must be doing something wrong... I am new to threads.

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• Titanium TableViewRow classname with custom rows

  - by pancake

  I would like to know in what way the 'className' property of a Ti.UI.TableViewRow helps when creating custom rows. For example, I populate a tableview with custom rows in the following way: function populateTableView(tableView, data) { var rows = []; var row; var title, image; var i; for (i = 0; i < data.length; i++) { title = Ti.UI.createLabel({ text : data[i].title, width : 100, height: 30, top: 5, left: 25 }); image = Ti.UI.createImage({ image : 'some_image.png', width: 30, height: 30, top: 5, left: 5 }); /* and, like, 5+ more views or whatever */ row = Ti.UI.createTableViewRow(); row.add(titleLabel); row.add(image); rows.push(row); } tableView.setData(rows); } Of course, this example of a "custom" row is easily created using the standard title and image properties of the TableViewRow, but that isn't the point. How is the allocation of new labels, image views and other child views of a table view prevented in favour of their reuse? I know in iOS this is achieved by using the method -[UITableView dequeueReusableCellWithIdentifier:] to fetch a row object from a 'reservoir' (so 'className' is 'identifier' here) that isn't currently being used for displaying data, but already has the needed child views laid out correctly in it, thus only requiring to update the data contained within (text, image data, etc). As this system is so unbelievably simple, I have a lot of trouble believing the method employed by the Titanium API does not support this. After reading through the API and searching the web, I do however suspect this is the case. The 'className' property is recommended as an easy way to make table views more efficient in Titanium, but its relation to custom table view rows is not explained in any way. If anyone could clarify this matter for me, I would be very grateful.

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• SQLAlchemy sessions - DetachedInstanceError?

  - by benjaminhkaiser

  I have a function that attempts to take a list of usernames, look each one up in a user table, and then add them to a membership table. If even one username is invalid, I want the entire list to be rolled back, including any users that have already been processed. I thought that using sessions was the best way to do this but I'm running into a DetachedInstanceError: DetachedInstanceError: Instance <Organization at 0x7fc35cb5df90> is not bound to a Session; attribute refresh operation cannot proceed Full stack trace is here. The error seems to trigger when I attempt to access the user (model) object that is returned by the query. From my reading I understand that it has something to do with there being multiple sessions, but none of the suggestions I saw on other threads worked for me. Code is below: def add_members_in_bulk(organization_eid, users): """Add users to an organization in bulk - helper function for add_member()""" """Returns "success" on success and id of first failed student on failure""" session = query_session.get_session() session.begin_nested() users = users.split('\n') for u in users: try: user = user_lookup.by_student_id(u) except ObjectNotFoundError: session.rollback() return u if user: membership.add_user_to_organization( user.entity_id, organization_eid, '', [] ) session.flush() session.commit() return 'success' here's the membership.add_user_to_organization: def add_user_to_organization(user_eid, organization_eid, title, tag_ids): """Add a User to an Organization with the given title""" user = user_lookup.by_eid(user_eid) organization = organization_lookup.by_eid(organization_eid) new_membership = OrganizationMembership( organization_eid=organization.entity_id, user_eid=user.entity_id, title=title) new_membership.tags = [get_tag_by_id(tag_id) for tag_id in tag_ids] crud.add(new_membership) and here is the lookup by ID query: def by_student_id(student_id, include_disabled=False): """Get User by RIN""" try: return get_query_set(include_disabled).filter(User.student_id == student_id).one() except NoResultFound: raise ObjectNotFoundError("User with RIN %s does not exist." % student_id)

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• Why won't WPF databindings show text when ToString() has a collaborating object?

  - by Jay

  In a simple form, I bind to a number of different objects -- some go in listboxes; some in textblocks. A couple of these objects have collaborating objects upon which the ToString() method calls when doing its work -- typically a formatter of some kind. When I step through the code I see that when the databinding is being set up, ToString() is called the collaborating object is not null and returns the expected result when inspected in the debugger, the objects return the expected result from ToString() BUT the text does not show up in the form. The only common thread I see is that these use a collaborating object, whereas the other bindings that show up as expected simply work from properties and methods of the containing object. If this is confusing, here is the gist in code: public class ThisThingWorks { private SomeObject some_object; public ThisThingWorks(SomeObject s) { some_object = s; } public override string ToString() { return some_object.name; } } public class ThisDoesntWork { private Formatter formatter; private SomeObject some_object; public ThisDoesntWork(SomeObject o, Formatter f) { formatter = f; some_object = o; } public override string ToString() { return formatter.Format(some_object.name); } } Again, let me reiterate -- the ToString() method works in every other context -- but when I bind to the object in WPF and expect it to display the result of ToString(), I get nothing. Update: The issue seems to be what I see as a buggy behaviour in the TextBlock binding. If I bind the Text property to a property of the DataContext that is declared as an interface type, ToString() is never called. If I change the property declaration to an implementation of the interface, it works as expected. Other controls, like Label work fine when binding the Content property to a DataContext property declared as either the implementation or the interface. Because this is so far removed from the title and content of this question, I've created a new question here: http://stackoverflow.com/questions/2917878/why-doesnt-textblock-databinding-call-tostring-on-a-property-whose-compile-tim

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• Setting the height of a row in a JTable in java

  - by Douglas Grealis

  I have been searching for a solution to be able to increase the height of a row in a JTable. I have been using the setRowHeight(int int) method which compiles and runs OK, but no row[s] have been increased. When I use the getRowHeight(int) method of the row I set the height to, it does print out the size I increased the row to, so I'm not sure what is wrong. The code below is a rough illustration how I am trying to solve it. My class extends JFrame. String[] columnNames = {"Column 1", "Column 2", "Column 1 3"}; JTable table = new JTable(new DefaultTableModel(columnNames, people.size())); DefaultTableModel model = (DefaultTableModel) table.getModel(); int count =1; for(Person p: people) { model.insertRow(count,(new Object[]{count, p.getName(), p.getAge()+"", p.getNationality})); count++; } table.setRowHeight(1, 15);//Try set height to 15 (I've tried higher) Can anyone tell me where I am going wrong? I am trying to increase the height of row 1 to 15 pixels?

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• What's the best way of accessing a DRb object (e.g. Ruby Queue) from Scala (and Java)?

  - by Tom Morris

  I have built a variety of little scripts using Ruby's very simple Queue class, and share the Queue between Ruby and JRuby processes using DRb. It would be nice to be able to access these from Scala (and maybe Java) using JRuby. I've put together something Scala and the JSR-223 interface to access jruby-complete.jar. import javax.script._ class DRbQueue(host: String, port: Int) { private var engine = DRbQueue.factory.getEngineByName("jruby") private var invoker = engine.asInstanceOf[Invocable] engine.eval("require \"drb\" ") private var queue = engine.eval("DRbObject.new(nil, \"druby://" + host + ":" + port.toString + "\")") def isEmpty(): Boolean = invoker.invokeMethod(this.queue, "empty?").asInstanceOf[Boolean] def size(): Long = invoker.invokeMethod(this.queue, "length").asInstanceOf[Long] def threadsWaiting: Long = invoker.invokeMethod(this.queue, "num_waiting").asInstanceOf[Long] def offer(obj: Any) = invoker.invokeMethod(this.queue, "push", obj.asInstanceOf[java.lang.Object]) def poll(): Any = invoker.invokeMethod(this.queue, "pop") def clear(): Unit = { invoker.invokeMethod(this.queue, "clear") } } object DRbQueue { var factory = new ScriptEngineManager() } (It conforms roughly to java.util.Queue interface, but I haven't declared the interface because it doesn't implement the element and peek methods because the Ruby class doesn't offer them.) The problem with this is the type conversion. JRuby is fine with Scala's Strings - because they are Java strings. But if I give it a Scala Int or Long, or one of the other Scala types (List, Set, RichString, Array, Symbol) or some other custom type. This seems unnecessarily hacky: surely there has got to be a better way of doing RMI/DRb interop without having to use JSR-223 API. I could either make it so that the offer method serializes the object to, say, a JSON string and takes a structural type of only objects that have a toJson method. I could then write a Ruby wrapper class (or just monkeypatch Queue) to would parse the JSON. Is there any point in carrying on with trying to access DRb from Java/Scala? Might it just be easier to install a real message queue? (If so, any suggestions for a lightweight JVM-based MQ?)

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• How to decide between using PLINQ and LINQ at runtime?

  - by Hamish Grubijan

  Or decide between a parallel and a sequential operation in general. It is hard to know without testing whether parallel or sequential implementation is best due to overhead. Obviously it will take some time to train "the decider" which method to use. I would say that this method cannot be perfect, so it is probabilistic in nature. The x,y,z do influence "the decider". I think a very naive implementation would be to give both 1/2 chance at the beginning and then start favoring them according to past performance. This disregards x,y,z, however. I suspect that this question would be better answered by academics than practitioners. Anyhow, please share your heuristic, your experience if any, your tips on this. Sample code: public interface IComputer { decimal Compute(decimal x, decimal y, decimal z); } public class SequentialComputer : IComputer { public decimal Compute( ... // sequential implementation } public class ParallelComputer : IComputer { public decimal Compute( ... // parallel implementation } public class HybridComputer : IComputer { private SequentialComputer sc; private ParallelComputer pc; private TheDecider td; // Helps to decide between the two. public HybridComputer() { sc = new SequentialComputer(); pc = new ParallelComputer(); td = TheDecider(); } public decimal Compute(decimal x, decimal y, decimal z) { decimal result; decimal time; if (td.PickOneOfTwo() == 0) { // Time this and save result into time. result = sc.Compute(...); } else { // Time this and save result into time. result = pc.Compute(); } td.Train(time); return result; } }

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• DO NOT BOTHER. THE PROBLEM IS NOT TRANSACTIONS. DUNNO HOW TO CLOSE / DELETE

  - by matti

  THE PROBLEM IS SOLVED. I DUNNO HOW TO CLOSE THIS QUESTION. ANOTHER SERVICE IS PROPABLY RUNNING AT ALMOST SAME SYNC THAT DOES THE THING. MY WORK "MATE" WILL HEAR A THING OR TWO IN THE MORNING. I have following code in windows service: data is in the dataset and it has been populated earlier and then rows are updated and inserted to dataset tables before calling code below. using (dataSetTxn = _cnctn.BeginTransaction()) { try { _somePlanAdptr.UpdateCommand.Transaction = dataSetTxn; _someLogAdptr.InsertCommand.Transaction = dataSetTxn; _someLinkAdptr.InsertCommand.Transaction = dataSetTxn; _someDataAdptr.InsertCommand.Transaction = dataSetTxn; _log.WriteDebug("Updating SomePlanAction"); _somePlanAdptr.Update(_ofDataSet, "SomePlanAction"); _log.WriteDebug(string.Format("Inserting {0} rows to SomeLog")); //error _someLogAdptr.Update(_ofDataSet, "SomeLog"); _log.WriteDebug(string.Format("Updating SomeLink with {0} rows", _ofDataSet.Tables["SomeLink"].Rows.Count)); _someLinkAdptr.Update(_ofDataSet, "SomeLink"); _log.WriteDebug(string.Format("Updating SomeData with {0} rows", _ofDataSet.Tables["SomeData"].Rows.Count)); _someDataAdptr.Update(_ofDataSet, "SomeData"); _log.WriteDebug("Commiting all changes to database."); dataSetTxn.Commit(); } catch (Exception e) { _log.WriteError("Updating database failed -> rollback", e); if (dataSetTxn != null && _cnctn.State == ConnectionState.Open) dataSetTxn.Rollback(); throw e; } } so one of the lines causes an exception log.WriteDebug(string.Format("Inserting {0} rows to SomeLog")); //error still the first adapter's data is updated to database. when debugged the data is not yet updated until the method that calls all (including this bit) exits. The method that does all is timed with System.Threading.Timer. Thanks & BR -Matti

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• Reference to the Main Form whilst trying to Serialize objects in C#

  - by Paul Matthews

  I have a button on my main form which calls a method to serialize some objects to disk. I am trying to add these objects to an ArrayList and then serialize them using a BinaryFormatter and a FileStream. public void SerializeGAToDisk(string GenAlgName) { // Let's make a list that includes all the objects we // need to store a GA instance ArrayList GAContents = new ArrayList(); GAContents.Add(GenAlgInstances[GenAlgName]); // Structure and info for a GA GAContents.Add(RunningGAs[GenAlgName]); // There may be several running GA's using (FileStream fStream = new FileStream(GenAlgName + ".ga", FileMode.Create, FileAccess.Write, FileShare.None)) { BinaryFormatter binFormat = new BinaryFormatter(); binFormat.Serialize(fStream, GAContents); } } When running the above code I get the following exception: System.Runtime.Serialization.SerializationException was unhandled Message=Type 'WindowsFormsApplication1.Form1' in Assembly 'GeneticAlgApp, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' is not marked as serializable. So that means that somewhere in the objects I'm trying to save there must be a reference to the main form. The only possible references I can see are 3 delegates which all point to methods in the main form code. Do delegates get serialized as well? I can't seem to apply the [NonSerialized] attribute to them. Is there anything else I might be missing? Even better, is there a quick method to find the reference(s) that are causing the problem?

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• Not delete params in URL, when sorting [ RAILS 3 ]

  - by kamil

  I have sortable table columns, made like that http://asciicasts.com/episodes/228-sortable-table-columns And I have simply filter options for two columns in table, made at select_tag (GET method). This two function don't work together. When I change filter, the sort parameter disappear and inversely. <th><%= sortable "Id" %></th> <th> Status<br/> <form method="get"> <%= select_tag(:status, options_for_select([['All', 'all']]+@statuses, params[:status]),{:onchange => 'this.form.submit()'}) %> </th> <th><%= sortable "Operation" %></th> <th> Processor<br/> <%= select_tag(:processor, options_for_select([['All', 'all']]+@processor_names, params[:processor]),{:onchange => 'this.form.submit()'}) %> </form> </th>

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• Cant insert a object into a silverlight databound combo box

  - by Steve

  Hi Until recently I had a combo box that was bound to a Linq queried IEnumerable of a DataService.Obj type in the bind method, and all worked fine private IEnumerable<DataService.Obj> _GeneralList; private IEnumerable<DataService.Obj> _QueriedList; private void Bind() { _GeneralList = SharedLists.GeneralList; _QueriedList = _GeneralList.Where(q =>q.ID >1000); cmbobox.ItemsSource = _QueriedList; } Then I had to change the method to insert a new obj and set that object as the default obj and now I get a "System.NullReferenceException: Object reference not set to an instance of an object" exception. I know this has to do with inserting into a linq queried ienumerable but I cant fix it. Any help will be gratefully received. private IEnumerable<DataService.Obj> _GeneralList; private IEnumerable<DataService.Obj> _QueriedList; private void Bind() { _GeneralList = SharedLists.GeneralList; _QueriedList = _GeneralList.Where(q =>q.ID >1000); cmbobox.ItemsSource = _QueriedList; DataService.Obj info = new DataService.Obj(); info.ID = "0"; (cmbobox.ItemsSource as ObservableCollection<DataService.Obj>).Insert(0,info); cmbobox.SelectedIndex = 0; } Thanks in advance

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• How to Implement an Interface that Requires Duplicate Member Names?

  - by Will Marcouiller

  I often have to implement some interfaces such as IEnumerable<T> in my code. Each time, when implementing automatically, I encounter the following: public IEnumerator<T> GetEnumerator() { // Code here... } public IEnumerator GetEnumerator1() { // Code here... } Though I have to implement both GetEnumerator() methods, they impossibly can have the same name, even if we understand that they do the same, somehow. The compiler can't treat them as one being the overload of the other, because only the return type differs. When doing so, I manage to set the GetEnumerator1() accessor to private. This way, the compiler doesn't complaint about not implementing the interface member, and I simply throw a NotImplementedException within the method's body. However, I wonder whether it is a good practice, or if I shall proceed differently, as perhaps a method alias or something like so. What is the best approach while implementing an interface such as IEnumerable<T> that requires the implementation of two different methods with the same name? EDIT #1 Does VB.NET reacts differently from C# while implementing interfaces, since in VB.NET it is explicitly implemented, thus forcing the GetEnumerator1(). Here's the code: Public Function GetEnumerator() As System.Collections.Generic.IEnumerator(Of T) Implements System.Collections.Generic.IEnumerable(Of T).GetEnumerator // Code here... End Function Public Function GetEnumerator1() As System.Collections.Generic.IEnumerator Implements System.Collections.Generic.IEnumerable.GetEnumerator // Code here... End Function Both GetEnumerator() methods are explicitly implemented, and the compile will refuse them to have the same name. Why?

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• C# performance methods of receiving data from a socket?

  - by Daniel

  Lets assume we have a simple internet socket, and its going to send 10 megabytes (because i want to ignore memory issues) of random data through. Is there any performance difference or a best practice method that one should use for receiving data? The final output data should be represented by a byte[]. Yes i know writing an arbitrary amount of data to memory is bad, and if I was downloading a large file i wouldn't be doing it like this. But for argument sake lets ignore that and assume its a smallish amount of data. I also realise that the bottleneck here is probably not the memory management but rather the socket receiving. I just want to know what would be the most efficient method of receiving data. A few dodgy ways can think of is: Have a List and a buffer, after the buffer is full, add it to the list and at the end list.ToArray() to get the byte[] Write the buffer to a memory stream, after its complete construct a byte[] of the stream.Length and read it all into it in order to get the byte[] output. Is there a more efficient/better way of doing this?

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• passing multidimensional arrays to function

  - by Pegah

  hi! I have a method in my class which uses a 3dimensional tfpairexp as input parameter. and I need to use the values in tfpairexp later. void calctfpairexp (int tf1, int tf2, double tfpairexp[][2][3]) { int ctr,c; for (int j = 0; j < cchips && (c = chips[j].crepls); j += c) { int ctrl_no=0; for (int *p = chips[j].ctrl ; p && (ctr=*p)>=0; ++p,ctrl_no++) { for (int k = 0; k < c; ++k) { tfpairexp[j][ctrl_no][k]=interactionFunc(2,3,1); } } } } I call the method inside the class like this: calctfpairexp(tf1,tf2,tfpairexp); and I need to use values inside tfpairexp in next lines. but the compiler gives error in this line: tfpairexp[j][ctrl_no][k]=interactionFunc(2,3,1); and says that the tfpairexp variable is not defined in the calctfpairexp function. any idea?

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• Should I pass a SqlDataReader by reference or not when passing it out to multiple threads.

  - by deroby

  Hi all, being new to c# I've run into this 'conundrum' when passing around a SqlDataReader between different threads. Without going into too much detail, the idea is to have a main thread fetching data from the database (a large recordset) and then have a helper-task run through this record by record and doing some stuff based upon the contents of this. There is no feedback to the recordset, it simply wades through until no records are left. This works fine, but given the nature of the job at hand it should be possible to have this job spread over different threads (CPUs) to maximize throughput (the order of execution is of no significance). The question then becomes, when I pass this recordset in a SqlDataReader, do I have to use ref or not ? It kind of boils down to the question : if I pass the object around without specifying ref, won't it create new copies in memory and have records processed n times ? Or, don't I risk having the record-position being moved forward while not all fields have been fully read yet ? The latter seems more like a 'data racing' issue and probably is covered by the lock()ing mechanism (or not?). My initial take on the problem was that it doesn't really hurt passing the variable using ref, yet as a colleague put it : "you only need ref when you're doing something wrong" =) Additionally using ref restricts me from applying a Using() construction too which isn't very nice either. I thus create a "basic" project that tackles the same approach but without the ref notation. Tests so far show that it works flawlessly on a Core2Duo (2cpu) using any number of threads, yet I'm still a bit wary... What do you experts think about this ? Use ref or not ? You can find the test-project here as it seems I can't upload it to this question directly ?!? ps: it's just a test-project and I'm new to c#, so please be gentle on me when breaking down the code =P

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• Cannot overload function

  - by anio

  So I've got a templatized class and I want to overload the behavior of a function when I have specific type, say char. For all other types, let them do their own thing. However, c++ won't let me overload the function. Why can't I overload this function? I really really do not want to do template specialization, because then I've got duplicate the entire class. Here is a toy example demonstrating the problem: http://codepad.org/eTgLG932 The same code posted here for your reading pleasure: #include <iostream> #include <cstdlib> #include <string> struct Bar { std::string blah() { return "blah"; } }; template <typename T> struct Foo { public: std::string doX() { return m_getY(my_t); } private: std::string m_getY(char* p_msg) { return std::string(p_msg); } std::string m_getY(T* p_msg) { return p_msg->blah(); } T my_t; }; int main(int, char**) { Foo<char> x; Foo<Bar> y; std::cout << "x " << x.doX() << std::endl; return EXIT_SUCCESS; } Thank you everyone for your suggestions. Two valid solutions have been presented. I can either specialize the doX method, or specialize m_getY() method. At the end of the day I prefer to keep my specializations private rather than public so I'm accepting Krill's answer.

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• ZendX Jquery Decorator

  - by iJD

  How use partial decorator in Jquery Element I use this code for Form Element: $title = new Zend_Form_Element_Text('title'); $title->setRequired(true) ->setAttrib('class', 'inputbox') ->setLabel('Title'); $title->viewScript = 'RegElement.phtml'; $title->setDecorators( array( array('ViewScript', array('class' => 'RegElement')) ) ); But when i use Jquery Element i dont know how implement it: $datePicker = new ZendX_JQuery_Form_Element_DatePicker( "datePicker1", array("label" => "Date:") ); $datePicker->viewScript = 'RegElement.phtml'; $datePicker->setDecorators( array( array('ViewScript', array('class' => 'RegElement')) ) ); //views/scripts/RegElement.phtml <li class="row <?php echo $this->class ?>"> <div class="cont-error"> <?php echo $this->formErrors($this->element->getMessages()); ?> </div> <div class="rowfields"> <?php echo $this->formLabel($this->element->getName(), $this->element->getLabel()) ?> <?php echo $this->{$this->element->helper}( $this->element->getName(), $this->element->getValue(), $this->element->getAttribs() ) ?> </div> <div class="hint"><?php echo $this->element->getDescription() ?></div> </li> And display this error: Warning: Exception caught by form: Cannot render jQuery form element without at least one decorator implementing the 'ZendX_JQuery_Form_Decorator_UiWidgetElementMarker' interface. I need display datePicker with same format. but idk how implement this interface. thx for your help.

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• Selecting a form which is in an iframe using jQuery

  - by Khnle

  I have a form inside an iframe which is inside a jQuery UI dialog box. The form contains a file input type. The jQuery UI dialog contains an Upload button. When this button is clicked, I would like to programmatically call the submit method. My question is how I could select the form which is in a iframe using jQuery. The following code should clarify the picture: <div id="upload_file_picker_dlg" title="Upload file"> <iframe id="upload_file_iframe" src="/frame_src_url" frameborder=0 width=100% scrolling=no></iframe> </div> frame_src_url contains: <form action="/UploadTaxTable" enctype="multipart/form-data" method="post" id="upload-form"> <p>Select a file to be uploaded:</p> <p> <input type="file" name="datafile" size="60"> </p> The jQueryUI dialog box javascript code: $('#upload_file_picker_dlg').dialog({ ... buttons: { 'Close': function() { $(this).dialog('close'); }, 'Upload': function() { $('#upload-form').submit(); //question is related to this line $(this).dialog('close'); } }, .... }); From the javascript code snippet above, how can I select the form with id upload-form that is in the iframe whose id is upload_file_iframe ?

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