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• How do you save and retrieve a Key/IV pair securely?

  - by Shawn Steward

  I'm using VB.Net's RijndaelManaged (RM) to encrypt files, using the RM.GenerateKey and RM.GenerateIV methods to generate the Key and IV and encrypting the file using the CryptoStream class. I'm planning on saving this Key and IV to a file and want to make sure I'm doing it the right way. I am combining the IV+Key, and encrypting that with my RSA Public key and writing it out to a file. Then, to decrypt I use the RSA Private key on this file to get the IV+Key, split them up and set RM.Key and RM.IV to these values and run the decryptor. Is this the best method to accomplish this, or is there a preferred method for saving the IV & Key? Also, what's the best way to construct and deconstruct the byte array? I used the .Concat method to join them together and that seems to work well but I can't seem to find something as easy to deconstruct it. I played with the .Take method that takes the first x # of bytes and it works for the first part but can't find anything that gets the rest of it.

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• iPhone OS: Get a list of methods and variables from anonymous object

  - by ChrisOPeterson

  I am building my first iPhone/Obj-c app and I have a large amount of data-holding subclasses that I am passing into a cite function. To the cite function these objects are anonymous and I need to find a way to access all the variables of each passed object. I have been using a pre-built NSArray and Selectors to do this but with more than 30 entries (and growing) it is kind of silly to do manually. There has to be a way to dynamically look up all the variables of an anonymous object. The obj-c runtime run-time docs mention this problem but from what I can tell this is not available in iPhone OS. If it is then I don't understand the implementation and need some guidance. A similar question was asked before but again I think they were talking about OSX and not iPhone. Any thoughts? -(NSString*)cite:(id)source { NSString *sourceClass = NSStringFromClass([source class]); // Runs through all the variables in the manually built methodList for(id method in methodList) { SEL x = NSSelectorFromString(method); // further implementation // Should be something like NSArray *methodList = [[NSArray alloc] initWithObjects:[source getVariableList]] for(id method in methodList) { SEL x = NSSelectorFromString(method); // Further implementation }

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• Increment part of a string in Ruby

  - by Rik

  I have a method in a Ruby script that is attempting to rename files before they are saved. It looks like this: def increment (path) if path[-3,2] == "_#" print " Incremented file with that name already exists, renaming\n" count = path[-1].chr.to_i + 1 return path.chop! << count.to_s else print " A file with that name already exists, renaming\n" return path << "_#1" end end Say you have 3 files with the same name being saved to a directory, we'll say the file is called example.mp3. The idea is that the first will be saved as example.mp3 (since it won't be caught by if File.exists?("#{file_path}.mp3") elsewhere in the script), the second will be saved as example_#1.mp3 (since it is caught by the else part of the above method) and the third as example_#2.mp3 (since it is caught by the if part of the above method). The problem I have is twofold. 1) if path[-3,2] == "_#" won't work for files with an integer of more than one digit (example_#11.mp3 for example) since the character placement will be wrong (you'd need it to be path[-4,2] but then that doesn't cope with 3 digit numbers etc). 2) I'm never reaching problem 1) since the method doesn't reliably catch file names. At the moment it will rename the first to example_#1.mp3 but the second gets renamed to the same thing (causing it to overwrite the previously saved file). This is possibly too vague for Stack Overflow but I can't find anything that addresses the issue of incrementing a certain part of a string. Thanks in advance!

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• SAX Parser Exceprtion

  - by sairam333

  When I run my application the following error willl be occured some times only,Can u explain why it is occured some times only and what i sthe solution for this and the error message is 03-13 14:38:18.055: WARN/System.err(1866): org.xml.sax.SAXParseException: expected: '' actual: '?' (position:END_TAG @137:35 in java.io.StringReader@438e0ef0) 03-13 14:38:18.064: WARN/System.err(1866): at org.apache.harmony.xml.parsers.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:151) 03-13 14:38:18.074: WARN/System.err(1866): at com.fitzengineering.teslaworldnet.interfacelayer.ParseXMLString.convertPeoples(ParseXMLString.java:484) 03-13 14:38:18.074: WARN/System.err(1866): at com.fitzengineering.teslaworldnet.presentationlayer.People.onCreate(People.java:91) 03-13 14:38:18.074: WARN/System.err(1866): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123) 03-13 14:38:18.084: WARN/System.err(1866): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2231) 03-13 14:38:18.095: WARN/System.err(1866): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2284) 03-13 14:38:18.104: WARN/System.err(1866): at android.app.ActivityThread.access$1800(ActivityThread.java:112)03-13 14:38:18.104: WARN/System.err(1866): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1692) 03-13 14:38:18.114: WARN/System.err(1866): at android.os.Handler.dispatchMessage(Handler.java:99) 03-13 14:38:18.124: WARN/System.err(1866): at android.os.Looper.loop(Looper.java:123) 03-13 14:38:18.134: WARN/System.err(1866): at android.app.ActivityThread.main(ActivityThread.java:3948) 03-13 14:38:18.134: WARN/System.err(1866): at java.lang.reflect.Method.invokeNative(Native Method) 03-13 14:38:18.144: WARN/System.err(1866): at java.lang.reflect.Method.invoke(Method.java:521) 03-13 14:38:18.144: WARN/System.err(1866): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:782) 03-13 14:38:18.154: WARN/System.err(1866): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:540) 03-13 14:38:18.154: WARN/System.err(1866): Thanks in advance

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• Java - Thread problem

  - by Yatendra Goel

  My question is related to all those methods(including Thread.sleep(...)) which throw InterruptedException. I found a statement on Sun's tutorial saying InterruptedException is an exception that sleep throws when another thread interrupts the current thread while sleep is active. Is that means that the interrupt will be ignored if the sleep is not active at the time of interrupt? Suppose I have two threads: threadOne and threadTwo. threadOne creates and starts threadTwo. threadTwo executes a runnable whose run method is something like: public void run() { : : try { Thread.sleep(10 * 1000); } catch (InterruptedException e) { return; } : : : // In the middle of two sleep invocations : : try { Thread.sleep(10 * 1000); } catch (InterruptedException e) { return; } : : } After thread creation, threadOne interrupts threadTwo. Suppose the threadTwo is in the middle of two sleep invocations at the time of interrupt (when no sleep method was active), then will the second sleep method throw InterrupteException as soon as it is invoked? If not, then will this interrupt will be ignored forever? How to be sure that threadTwo will always know about the interrupt (doesn't matter whether its one of the sleep method is active or not)?

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• uniimageview not updating after views tranistion

  - by Fabio Ricci

  Hi I have one main view where I display an image, in the method viewDidLoad: ballRect = CGRectMake(posBallX, 144, 32.0f, 32.0f); theBall = [[UIImageView alloc] initWithFrame:ballRect]; [theBall setImage:[UIImage imageNamed:@"ball.png"]]; [self.view addSubview:theBall]; [laPalla release]; Obviously, the value of posBallX is defined and then update via a custom method call many times in the same class. theBall.frame = CGRectMake(posBallX, 144, 32, 32); Everything works, but when I go to another view with [self presentModalViewController:viewTwo animated:YES]; and come back with [self presentModalViewController:viewOne animated:YES]; the image is displayed correctly after the method viewDidLoad is called (I retrieve the values with NSUserDefaults) but no more in the second method. In the NSLog I can even see the new posBallX updating correctly, but the Image is simply no more shown... The same happens with a Label as well, which should print the value of posBallX. So, things are just not working if I come back to the viewOne from the viewTwo... Any idea??????? Thanks so much!

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• How does static code run with multiple threads?

  - by Krisc

  I was reading http://stackoverflow.com/questions/1511798/threading-from-within-a-class-with-static-and-non-static-methods and I am in a similar situation. I have a static method that pulls data from a resource and creates some runtime objects based on the data. static class Worker{ public static MyObject DoWork(string filename){ MyObject mo = new MyObject(); // ... does some work return mo; } } The method takes awhile (in this case it is reading 5-10mb files) and returns an object. I want to take this method and use it in a multiple thread situation so I can read multiple files at once. Design issues / guidelines aside, how would multiple threads access this code? Let's say I have something like this... class ThreadedWorker { public void Run() { Thread t = new Thread(OnRun); t.Start(); } void OnRun() { MyObject mo = Worker.DoWork("somefilename"); mo.WriteToConsole(); } } Does the static method run for each thread, allowing for parallel execution?

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• Redirecting users after destroy

  - by mathee

  I have 3 models: Questions, Answers, and Profiles (I know, it should be called "Users"). When you view a question Q, I query the database for the answers to Q. (They are linked by id.) In the view, the current user has the option to delete his answer by clicking on the destroy link displayed next to his answer: %table %tr %td Answers: - @answers.each do |a| %tr %td - @provider = Profile.find(a.provider) %i #{h @provider.username} said: %br #{h a.description} %td = link_to 'View full answer', a %td - if a.provider == @profile.id #{link_to 'Delete my answer', a, :confirm => 'Are you sure?', :method => :delete} The problem is that when the user clicks on the destroy link, it redirects to the /answers/index. I want it to redirect to /questions/Q. What's the best way to do this? I know that there's a redirect_to method, but I don't know how to implement it when I want to redirect to an action for a different controller. It also needs to remember the question from which the answer is being deleted. I tried passing something like :question_id in link_to as: #{link_to 'Delete my answer', a, :confirm => 'Are you sure?', :question_id => @question.id, :method => :delete} In AnswersController#destroy: def destroy @answer = Answer.find(params[:id]) @answer.destroy respond_to do |format| format.html { redirect_to(answers_url) } format.xml { head :ok } end @question = Question.find(params[:question_id]) redirect_to question_path(@question) end The :question_id information is not passed to the destroy method, so I get this error: Couldn't find Question without an ID To confirm, I added a puts call before Question.find, and it returned nil.

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• The uncatchable exception, pt 2

  - by chaiguy

  Ok I've done some testing and I've reduced the problem to something very simple: i. Create a method in a new class that throws an exception: public class Class1 { public void CallMe() { string blah = null; blah.ToLower(); } } ii. Create a MethodInfo that points to this method somewhere else: Type class1 = typeof( Class1 ); Class1 obj = new Class1(); MethodInfo method = class1.GetMethod( "CallMe" ); iii. Wrap a call to Invoke() in a try/catch block: try { method.Invoke( obj, null ); // exception is not being caught! } catch { } iv. Run the program without the debugger (works fine). v. Now run the program with the debugger. The debugger will halt the program when the exception occurs, even though it's wrapped in a catch handler that tries to ignore it. (Even if you put a breakpoint in the catch block it will halt before it reaches it!) In fact, the exception is happening when you run it without the debugger too. In a simple test project it's getting ignored at some other level, but if your app has any kind of global exception handling, it will get triggered there as well. This is causing me a real headache because it keeps triggering my app's crash-handler, not to mention the pain it is to attempt to debug.

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• How to implement an interface class using the non-virtual interface idiom in C++?

  - by andreas buykx

  Hi all, In C++ an interface can be implemented by a class with all its methods pure virtual. Such a class could be part of a library to describe what methods an object should implement to be able to work with other classes in the library: class Lib::IFoo { public: virtual void method() = 0; }; : class Lib::Bar { public: void stuff( Lib::IFoo & ); }; Now I want to to use class Lib::Bar, so I have to implement the IFoo interface. For my purposes I need a whole of related classes so I would like to work with a base class that guarantees common behavior using the NVI idiom: class FooBase : public IFoo // implement interface IFoo { public: void method(); // calls methodImpl; private: virtual void methodImpl(); }; The non-virtual interface (NVI) idiom ought to deny derived classes the possibility of overriding the common behavior implemented in FooBase::method(), but since IFoo made it virtual it seems that all derived classes have the opportunity to override the FooBase::method(). If I want to use the NVI idiom, what are my options other than the pImpl idiom already suggested (thanks space-c0wb0y).

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• String Length Evaluating Incorrectly

  - by Justin R.

  My coworker and I are debugging an issue in a WCF service he's working on where a string's length isn't being evaluated correctly. He is running this method to unit test a method in his WCF service: // Unit test method public void RemoveAppGroupTest() { string addGroup = "TestGroup"; string status = string.Empty; string message = string.Empty; appActiveDirectoryServicesClient.RemoveAppGroup("AOD", addGroup, ref status, ref message); } // Inside the WCF service [OperationBehavior(Impersonation = ImpersonationOption.Required)] public void RemoveAppGroup(string AppName, string GroupName, ref string Status, ref string Message) { string accessOnDemandDomain = "MyDomain"; RemoveAppGroupFromDomain(AppName, accessOnDemandDomain, GroupName, ref Status, ref Message); } public AppActiveDirectoryDomain(string AppName, string DomainName) { if (string.IsNullOrEmpty(AppName)) { throw new ArgumentNullException("AppName", "You must specify an application name"); } } We tried to step into the .NET source code to see what value string.IsNullOrEmpty was receiving, but the IDE printed this message when we attempted to evaluate the variable: 'Cannot obtain value of local or argument 'value' as it is not available at this instruction pointer, possibly because it has been optimized away.' (None of the projects involved have optimizations enabled). So, we decided to try explicitly setting the value of the variable inside the method itself, immediately before the length check -- but that didn't help. // Lets try this again. public AppActiveDirectoryDomain(string AppName, string DomainName) { // Explicitly set the value for testing purposes. AppName = "AOD"; if (AppName == null) { throw new ArgumentNullException("AppName", "You must specify an application name"); } if (AppName.Length == 0) { // This exception gets thrown, even though it obviously isn't a zero length string. throw new ArgumentNullException("AppName", "You must specify an application name"); } } We're really pulling our hair out on this one. Has anyone else experienced behavior like this? Any tips on debugging it?

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• Interpreting java.lang.NoSuchMethodError message

  - by Doog

  I get the following runtime error message (along with the first line of the stack trace, which points to line 94). I'm trying to figure out why it says no such method exists. java.lang.NoSuchMethodError: com.sun.tools.doclets.formats.html.SubWriterHolderWriter.printDocLinkForMenu( ILcom/sun/javadoc/ClassDoc;Lcom/sun/javadoc/MemberDoc; Ljava/lang/String;Z)Ljava/lang/String; at com.sun.tools.doclets.formats.html.AbstractExecutableMemberWriter.writeSummaryLink( AbstractExecutableMemberWriter.java:94) Line 94 of writeSummaryLink is shown below. QUESTIONS What does "ILcom" or "Z" mean? Why there are four types in parentheses (ILcom/sun/javadoc/ClassDoc;Lcom/sun/javadoc/MemberDoc;Ljava/lang/String;Z) and one after the parentheses Ljava/lang/String; when the method printDocLinkForMenu clearly has five parameters? CODE DETAIL The writeSummaryLink method is: protected void writeSummaryLink(int context, ClassDoc cd, ProgramElementDoc member) { ExecutableMemberDoc emd = (ExecutableMemberDoc)member; String name = emd.name(); writer.strong(); writer.printDocLinkForMenu(context, cd, (MemberDoc) emd, name, false); // 94 writer.strongEnd(); writer.displayLength = name.length(); writeParameters(emd, false); } Here's the method line 94 is calling: public void printDocLinkForMenu(int context, ClassDoc classDoc, MemberDoc doc, String label, boolean strong) { String docLink = getDocLink(context, classDoc, doc, label, strong); print(deleteParameterAnchors(docLink)); }

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• MediaFileUpload of HTML in UTF-8 encoding using Python and Google-Drive-SDK

  - by Victoria

  Looking for example using MediaFileUpload has a reference to the basic documentation for creating/uploading a file to Google Drive. However, while I have code that creates files, converting from HTML to Google Doc format. It works perfectly when they contain only ASCII characters, but when I add a non-ASCII character, it fails, with the following traceback: Traceback (most recent call last): File "d:\my\py\ckwort.py", line 949, in <module> rids, worker_documents = analyze( meta, gd ) File "d:\my\py\ckwort.py", line 812, in analyze gd.mkdir( **iy ) File "d:\my\py\ckwort.py", line 205, in mkdir self.create( **( kw['subop'])) File "d:\my\py\ckwort.py", line 282, in create media_body=kw['media_body'], File "D:\my\py\gdrive2\oauth2client\util.py", line 120, in positional_wrapper return wrapped(*args, **kwargs) File "D:\my\py\gdrive2\apiclient\http.py", line 676, in execute headers=self.headers) File "D:\my\py\gdrive2\oauth2client\util.py", line 120, in positional_wrapper return wrapped(*args, **kwargs) File "D:\my\py\gdrive2\oauth2client\client.py", line 420, in new_request redirections, connection_type) File "D:\my\py\gdrive2\httplib2\__init__.py", line 1597, in request (response, content) = self._request(conn, authority, uri, request_uri, method, body, headers, redirections, cachekey) File "D:\my\py\gdrive2\httplib2\__init__.py", line 1345, in _request (response, content) = self._conn_request(conn, request_uri, method, body, headers) File "D:\my\py\gdrive2\httplib2\__init__.py", line 1282, in _conn_request conn.request(method, request_uri, body, headers) File "C:\Python27\lib\httplib.py", line 958, in request self._send_request(method, url, body, headers) File "C:\Python27\lib\httplib.py", line 992, in _send_request self.endheaders(body) File "C:\Python27\lib\httplib.py", line 954, in endheaders self._send_output(message_body) File "C:\Python27\lib\httplib.py", line 812, in _send_output msg += message_body UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 370: ordinal not in range(128) I don't find any parameter to use to specify what file encoding should be used by MediaFileUpload (My files are using UTF-8). Am I missing something?

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• How can I create/update an XML node that may or may not exist?

  - by ScottBai

  Is there a method available (i.e. without me creating my own recursive method), for a given xpath (or other method of identifying the hierarchical position) to create/update an XML node, where the node would be created if it does not exist? This would need to create the parent node if it does not exist as well. I do have an XSD which includes all possible nodes. i.e. Before: <employee> <name>John Smith</name> </employee> Would like to call something like this: CoolXmlUpdateMethod("/employee/address/city", "Los Angeles"); After: <employee> <name>John Smith</name> <address> <city>Los Angeles</city> </address> </employee> Or even a method to create a node, given an xpath, wherein it will recursively create the parent node(s) if they do not exist? As far as the application (if it matters), this is taking an existing XML doc that contains only populated nodes, and adding data to it from another system. The new data may or may not already have values populated in the source XML. Surely this is not an uncommon scenario?

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• A bit confused about OOP and PHP.

  - by Pirkka

  Hello I have programmed with procedural style a lot before and in these few months I have decided to go OOP. Im a bit confused about OOP and PHP. Lets say I have Categories table and Pages table in my database. I would like to do a page-class and a category-class. Lets say I would have a page that showed information about the category and there would be a list of pages that belong to the category. How would I implement that in OOP way? I have thought that the category class would have a property (array) that would contain all the pages that it has. Well then comes the part that I`m confused about. Should I have a method that would get all the pages with correct categoryID from the database and should I instantiate all the rows as an Page-object? Or should I have a setPages-method in the Category-class and getAllPages-method in the Pages-class and with that method I would set all the pages to the Category-class. Huh Im lost. :D

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• How to create an instance of object with RTTI in Delphi 2010?

  - by Paul

  As we all known, when we call a constructor of a class like this: instance := TSomeClass.Create; The Delphi compiler actually do the following things: Call the static NewInstance method to allocate memory and initialize the memory layout. Call the constructor method to perform the initialization of the class Call the AfterConstruction method It's simple and easy to understand. but I'm not very sure how the compiler handle exceptions in the second and the third step. It seems there are no explicit way to create an instance using a RTTI constructor method in D2010. so I wrote a simple function in the Spring Framework for Delphi to reproduce the process of the creation. class function TActivator.CreateInstance(instanceType: TRttiInstanceType; constructorMethod: TRttiMethod; const arguments: array of TValue): TObject; var classType: TClass; begin TArgument.CheckNotNull(instanceType, 'instanceType'); TArgument.CheckNotNull(constructorMethod, 'constructorMethod'); classType := instanceType.MetaclassType; Result := classType.NewInstance; try constructorMethod.Invoke(Result, arguments); except on Exception do begin if Result is TInterfacedObject then begin Dec(TInterfacedObjectHack(Result).FRefCount); end; Result.Free; raise; end; end; try Result.AfterConstruction; except on Exception do begin Result.Free; raise; end; end; end; I feel it maybe not 100% right. so please show me the way. Thanks!

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• NSOperations or NSThread for bursts of smaller tasks that continuously cancel each other?

  - by RickiG

  Hi I would like to see if I can make a "search as you type" implementation, against a web service, that is optimized enough for it to run on an iPhone. The idea is that the user starts typing a word; "Foo", after each new letter I wait XXX ms. to see if they type another letter, if they don't, I call the web service using the word as a parameter. The web service call and the subsequent parsing of the result I would like to move to a different thread. I have written a simple SearchWebService class, it has only one public method: - (void) searchFor:(NSString*) str; This method tests if a search is already in progress (the user has had a XXX ms. delay in their typing) and subsequently stops that search and starts a new one. When a result is ready a delegate method is called: - (NSArray*) resultsReady; I can't figure out how to get this functionality 'threaded'. If I keep spawning new threads each time a user has a XXX ms. delay in the typing I end up in a bad spot with many threads, especially because I don't need any other search, but the last one. Instead of spawning threads continuously, I have tried keeping one thread running in the background all the time by: - (void) keepRunning { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; SearchWebService *searchObj = [[SearchWebService alloc] init]; [[NSRunLoop currentRunLoop] run]; //keeps it alive [searchObj release]; [pool release]; } But I can't figure out how to access the "searchFor" method in the "searchObj" object, so the above code works and keeps running. I just can't message the searchObj or retrieve the resultReady objects? Hope someone could point me in the right direction, threading is giving me grief:) Thank you.

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• Java XHTML Doclet: fatal exception

  - by Cheeso

  Has anyone used XHTML Doclet, and can you provide some hints as to how to get it to work successfully? I run it like this: \sunjdk\bin\javadoc -doclet net.sourceforge.xhtmldoclet.Doclet -docletpath c:\sw\java\XHTML_Doclet_0.4.jar -d <output> [class files here] (all on one line) When I run it I get this: javadoc: error - In doclet class net.sourceforge.xhtmldoclet.Doclet, method validOptions has thrown an exception java.lang.reflect.InvocationTargetException java.lang.Error: Fatal: Resource (net.sourceforge.xhtmldoclet.resources.doclet) for javadoc doclets is missing. at com.sun.tools.doclets.internal.toolkit.util.MessageRetriever.getText(MessageRetriever.java:110) at com.sun.tools.doclets.internal.toolkit.util.MessageRetriever.getText(MessageRetriever.java:92) at com.sun.tools.doclets.internal.toolkit.util.MessageRetriever.getText(MessageRetriever.java:81) at com.sun.tools.doclets.internal.toolkit.Configuration.getText(Configuration.java:634) at com.sun.tools.doclets.internal.toolkit.Configuration.generalValidOptions(Configuration.java:515) at net.sourceforge.xhtmldoclet.Config.validOptions(Unknown Source) at net.sourceforge.xhtmldoclet.Doclet.validOptions(Unknown Source) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at com.sun.tools.javadoc.DocletInvoker.invoke(DocletInvoker.java:269) at com.sun.tools.javadoc.DocletInvoker.validOptions(DocletInvoker.java:198) at com.sun.tools.javadoc.Start.parseAndExecute(Start.java:317) at com.sun.tools.javadoc.Start.begin(Start.java:128) at com.sun.tools.javadoc.Main.execute(Main.java:41) at com.sun.tools.javadoc.Main.main(Main.java:31) 1 error It seems like it ought to just work. What am I doing wrong?

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• How best to associate code with events in jQuery?

  - by Ned Batchelder

  Suppose I have a <select> element on my HTML page, and I want to run some Javascript when the selection is changed. I'm using jQuery. I have two ways to associate the code with the element. Method 1: jQuery .change() <select id='the_select'> <option value='opt1'>One</option> <option value='opt2'>Two</option> </select> <script> $('#the_select').change(function() { alert('Changed!'); }); </script> Method 2: onChange attribute <select id='the_select' onchange='selectChanged();'> <option value='opt1'>One</option> <option value='opt2'>Two</option> </select> <script> function selectChanged() { alert('Changed!'); } </script> I understand the different modularity here: for example, method 1 keeps code references out of the HTML, but method 2 doesn't need to mention HTML ids in the code. What I don't understand is: are there operational differences between these two that would make me prefer one over the other? For example, are there edge-case browsers where one of these works and the other doesn't? Is the integration with jQuery better for either? Does the late-binding of the code to the event make a difference in the behavior of the page? Which do you pick and why?

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• The new operator in C# isn't overriding base class member

  - by Dominic Zukiewicz

  I am confused as to why the new operator isn't working as I expected it to. Note: All classes below are defined in the same namespace, and in the same file. This class allows you to prefix any content written to the console with some provided text. public class ConsoleWriter { private string prefix; public ConsoleWriter(string prefix) { this.prefix = prefix; } public void Write(string text) { Console.WriteLine(String.Concat(prefix,text)); } } Here is a base class: public class BaseClass { protected static ConsoleWriter consoleWriter = new ConsoleWriter(""); public static void Write(string text) { consoleWriter.Write(text); } } Here is an implemented class: public class NewClass : BaseClass { protected new static ConsoleWriter consoleWriter = new ConsoleWriter("> "); } Now here's the code to execute this: class Program { static void Main(string[] args) { BaseClass.Write("Hello World!"); NewClass.Write("Hello World!"); Console.Read(); } } So I would expect the output to be Hello World! > Hello World! But the output is Hello World Hello World I do not understand why this is happening. Here is my thought process as to what is happening: The CLR calls the BaseClass.Write() method The CLR initialises the BaseClass.consoleWriter member. The method is called and executed with the BaseClass.consoleWriter variable Then The CLR calls the NewClass.Write() The CLR initialises the NewClass.consoleWriter object. The CLR sees that the implementation lies in BaseClass, but the method is inherited through The CLR executes the method locally (in NewClass) using the NewClass.consoleWriter variable I thought this is how the inheritance structure works? Please can someone help me understand why this is not working?

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• Create a Task list, with tasks without executing

  - by Ernesto Araya Eguren

  I have an async method private async Task DoSomething(CancellationToken token) a list of Tasks private List<Task> workers = new List<Task>(); and I have to create N threads that runs that method public void CreateThreads(int n) { tokenSource = new CancellationTokenSource(); token = tokenSource.Token; for (int i = 0; i < n; i++) { workers.Add(DoSomething(token)); } } but the problem is that those have to run at a given time public async Task StartAllWorkers() { if (0 < workers.Count) { try { while (0 < workers.Count) { Task finishedWorker = await Task.WhenAny(workers.ToArray()); workers.Remove(finishedWorker); finishedWorker.Dispose(); } if (workers.Count == 0) { tokenSource = null; } } catch (OperationCanceledException) { throw; } } } but actually they run when i call the CreateThreads Method (before the StartAllWorkers). I searched for keywords and problems like mine but couldn't find anything about stopping the task from running. I've tried a lot of different aproaches but anything that could solve my problem entirely. For example, moving the code from DoSomething into a workers.Add(new Task(async () => { }, token)); would run the StartAllWorkers(), but the threads will never actually start. There is another method for calling the tokenSource.Cancel().

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• .NET: How to pass value when subscribing to event and obtain it when the event is triggered (Dynamic

  - by Entrase

  The task is to create event handlers in runtime. I need the one method to be called with different parameter value for different events. The events and their number are only known in runtime. So I'm trying to generate dynamic methods, each of which will be assigned to some event, but in general they all just pass some value to an instance method and call it. It would be great if something similar could be done the easier way. I mean passing some value at subscribing stage and then obtaining it when the event is triggered. This is what I'm trying to do now: public class EventSource { public event EventHandler eventOne; public event EventHandler eventTwO; public event EventHandler eventThree; } public class EventListener { SubscribeForEvents() { BindingFlags flags = BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance; // Suppose we've already got EventInfo // and target source somewhere // so we can do eventInfo.AddEventHandler(target, delegate) // Now we need a delegate. int value = 42; Type tDelegate = eventInfo.EventHandlerType; // http://msdn.microsoft.com/en-us/library/ms228976(VS.95).aspx Type returnType = GetDelegateReturnType(tDelegate); DynamicMethod listener = new DynamicMethod("", null, GetDelegateParameterTypes(tDelegate), this.GetType()); ///////// Type[] callParameters = { typeof(int) }; MethodInfo method = this.GetType().GetMethod("ToCallFromDelegate", flags); ILGenerator generator = listener.GetILGenerator(); // No success in this mess. What's wrong? generator.Emit(OpCodes.Ldc_I4, value); generator.Emit(OpCodes.Call, method); generator.Emit(OpCodes.Pop); generator.Emit(OpCodes.Ret); ///////////// Delegate delegate = listener.CreateDelegate(tDelegate); eventInfo.AddEventHandler(target, delegate); // When triggered, there is InvalidProgramException } void ToCallFromDelegate(int value) { doSomething(); } }

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• Two questions on ensuring EndInvoke() gets called on a list of IAsyncResult objects

  - by RobV

  So this question is regarding the .Net IAsyncResult design pattern and the necessity of calling EndInvoke as covered in this question Background I have some code where I'm firing off potentially many asynchronous calls to a particular function and then waiting for all these calls to finish before using EndInvoke() to get back all the results. Question 1 I don't know whether any of the calls has encountered an exception until I call EndInvoke() and in the event that an exception occurs in one of the calls the entire method should fail and the exception gets wrapped into an API specific exception and thrown upwards. So my first question is what's the best way then to ensure that the remainder of the async calls get properly terminated? Is a finally block which calls EndInvoke() on the remainder of the unterminated calls (and ignores any further exceptions) the best way to do this? Question 2 Secondly when I first fire off all my asyc calls I then call WaitHandle.WaitAll() on the array of WaitHandle instances that I've got from my IAsyncResult instances. The method which is firing all these async calls has a timeout to adhere to so I provide this to the WaitAll() method. Then I test whether all the calls have completed, if not then the timeout must have been reached so the method should also fail and throw another API specific exception. So my second question is what should I do in this case? I need to call EndInvoke() to terminate all these async calls before I throw the error but at the same time I don't want the code to get stuck since EndInvoke() is blocking. In theory at least if the WaitAll() call times out then all the async calls should themselves have timed out and thrown exceptions (thus completing the call) since they are also governed by a timeout but this timeout is potentially different from the main timeout

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• Finding out max available print area

  - by Armagan

  I'm trying to find out max available area on my printer. I've printed a simple rectangle trying out different boundary variables. My question is, why doesn't first two work correctly? They don't print a full rectangle on the paper, only the left and top sides are drawn. Why does only the third one prints a full rectangle? I was under the impression of that all three should be working correctly. What am I missing? Here's my code: this.printDocument1.DefaultPageSettings.Margins = new Margins(0, 0, 0, 0); ... private void PrintPage(object sender, PrintPageEventArgs e) { //Method 1, no right and bottom sides are printed e.Graphics.DrawRectangle(new Pen(Color.Black, 1), e.PageBounds); //Method 2, same as Method 1 e.Graphics.DrawRectangle(new Pen(Color.Black, 1), e.MarginBounds); //Method 3, works correctly e.Graphics.DrawRectangle(new Pen(Color.Black, 1), new Rectangle((int)e.Graphics.VisibleClipBounds.X, (int)e.Graphics.VisibleClipBounds.Y, (int)e.Graphics.VisibleClipBounds.Width, (int)e.Graphics.VisibleClipBounds.Height)); }

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• Why thread in background is not waiting for task to complete?

  - by Haris Hasan

  I am playing with async await feature of C#. Things work as expected when I use it with UI thread. But when I use it in a non-UI thread it doesn't work as expected. Consider the code below private void Click_Button(object sender, RoutedEventArgs e) { var bg = new BackgroundWorker(); bg.DoWork += BgDoWork; bg.RunWorkerCompleted += BgOnRunWorkerCompleted; bg.RunWorkerAsync(); } private void BgOnRunWorkerCompleted(object sender, RunWorkerCompletedEventArgs runWorkerCompletedEventArgs) { } private async void BgDoWork(object sender, DoWorkEventArgs doWorkEventArgs) { await Method(); } private static async Task Method() { for (int i = int.MinValue; i < int.MaxValue; i++) { var http = new HttpClient(); var tsk = await http.GetAsync("http://www.ebay.com"); } } When I execute this code, background thread don't wait for long running task in Method to complete. Instead it instantly executes the BgOnRunWorkerCompleted after calling Method. Why is that so? What am I missing here? P.S: I am not interested in alternate ways or correct ways of doing this. I want to know what is actually happening behind the scene in this case? Why is it not waiting?

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