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Which plugin framework to use for native C++/Win32

- by Kerido

Hi everybody. I have an extensible product that allows 3rd party developers to extend it. The aspects that can be extended are documented and interfaces are provided in the SDK. Currently, I'm using COM and I'm getting pretty comfortable with it. I especially like the ability to provide interface versioning in a unified manner. I consider it to be a requirement because you never know what you're gonna need in the future. Just to be precise, here's an example. Let's suppose I have an interface representing a particular feature: class IFeature { public: virtual void DoFeatureTask() = 0; }; Then after the interface is already documented (and someone may have used it in the plugin code) I'm realizing, I need more from this feature. Maybe, there is an option I need to provide. I just define the second version: class IFeature2 { public: virtual void DoFeatureTask(int theOption) = 0; }; I don't mean I intend to have lots of versions. But it just may happen. In COM, because every interface is associated with a GUID, I can query a preferred implementation, determine its presence, and, finally, fall back to a legacy one. But after glancing through C++/COM-related questions, I noticed many recommendations against COM. So maybe it's not the best choice and I'm just too old-school. Can you advise on an alternative?

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How can you push a new view with a grouped table?

- by Tanner

Hi All, Ive been trying to push a new view when a cell is tapped but absolutely nothing happens. I figured grouped style pushed the same as plain. Here is my code: -(void)viewDidLoad { [super viewDidLoad]; contactArray = [[NSArray alloc] initWithObjects:@"iPhone",@"iPod",@"MacBook",@"MacBook Pro",nil]; shareArray = [[NSArray alloc] initWithObjects:@"Flex",@"AIR",@"PhotoShop",@"Flash",nil]; } -(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return 2; } // Customize the number of rows in the table view. -(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { if(section == 0) return [contactArray count]; else return [shareArray count]; } -(NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section{ if(section == 0){ return @"Contact"; }else{ return @"Share"; } } -(NSString *)tableView:(UITableView *)tableView titleForFooterInSection:(NSInteger)section{ if(section == 0){ return @"Footer for Apple Products"; }else{ return @"Footer for Adobe Softwares"; } } // Customize the appearance of table view cells. -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease]; } // Set up the cell... if(indexPath.section == 0){ cell.text = [contactArray objectAtIndex:indexPath.row]; }else{ cell.text = [shareArray objectAtIndex:indexPath.row]; } return cell; } -(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { //NextViewController *nextController = [[NextViewController alloc] initWithNibName:@"NextView" bundle:nil]; //[self.navigationController pushViewController:nextController animated:YES]; if([contactArray objectAtIndex:indexPath.row] == @"iPhone"){ LandscapeHydrogen *abo = [[LandscapeHydrogen alloc] initWithNibName:@"LandscapeHydrogen" bundle:nil]; [self.navigationController pushViewController:abo animated:NO]; [abo release]; } } Any help is appreciated.

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No Hibernate Exception on the same insert of data

- by Mark Estrada

Hi All, Hibernate Newbie here. I am quite unsure why I am not getting any exception when I am executing below code. On first attempt, this code creates the Book Entry on my Book Table. But my concern is that when I execute below code again, no error was pop out by Hibernate. I was in fact expecting some sort of Violation of Primary Key Constraints as what I have bee doing in JDBC code. public class BookDao { public void createBook(Book bookObj) { Session session = HibernateUtil.getSessionFactory() .getCurrentSession(); session.beginTransaction(); session.saveOrUpdate(bookObj); session.getTransaction().commit(); } } public class HibernateUtil { private static final SessionFactory sessionFactory = buildSessionFactory(); private static SessionFactory buildSessionFactory() { try { // Create the SessionFactory from hibernate.cfg.xml return new AnnotationConfiguration().configure() .buildSessionFactory(); } catch (Throwable ex) { // Make sure you log the exception, as it might be swallowed ex.printStackTrace(); throw new ExceptionInInitializerError(ex); } } public static SessionFactory getSessionFactory() { return sessionFactory; } } public class BookDBStarter { public static void main(String[] args) { Book bookHF = new Book(); bookHF.setIsbn("HF-12345"); bookHF.setName("Head First HTML"); bookHF.setPublishDate(new Date()); BookDao daoBook = new BookDao(); daoBook.createBook(bookHF); } } Is this normal hibernate way? And how will I know if my insert is successful? Any thoughts?

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leak in fgets when assigning to buffer

- by monkeyking

I'm having problems understanding why following code leaks in one case, and not in the other case. The difference is while(NULL!=fgets(buffer,length,file))//doesnt leak while(NULL!=(buffer=fgets(buffer,length,file))//leaks I thought it would be the same. Full code below. #include <stdio.h> #include <stdlib.h> #define LENS 10000 void no_leak(const char* argv){ char *buffer = (char *) malloc(LENS); FILE *fp=fopen(argv,"r"); while(NULL!=fgets(buffer,LENS,fp)){ fprintf(stderr,"%s",buffer); } fclose(fp); fprintf(stderr,"%s\n",buffer); free(buffer); } void with_leak(const char* argv){ char *buffer = (char *) malloc(LENS); FILE *fp=fopen(argv,"r"); while(NULL!=(buffer=fgets(buffer,LENS,fp))){ fprintf(stderr,"%s",buffer); } fclose(fp); fprintf(stderr,"%s\n",buffer); free(buffer); }

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Is it secure to use malloc?

- by Felix Guerrero

Somebody told me that allocating with malloc is not secure anymore, I'm not a C/C++ guru but I've made some stuff with malloc and C/C++. Does anyone know about what risks I'm into? Quoting him: [..] But indeed the weak point of C/C++ it is the security, and the Achilles' heel is indeed malloc and the abuse of pointers. C/C++ it is a well known insecure language. [..] There would be few apps in what I would not recommend to continue programming with C++."

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JApplet behaving unexpectedly

- by JohnW

import java.awt.Graphics; import java.awt.Image; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JApplet; import javax.swing.Timer; public class CountingSheep extends JApplet { private Image sheepImage; private Image backgroundImage; private GameBoard gameBoard; private scoreBoard scoreBoard; public void init() { loadImages(); gameBoard = new GameBoard(sheepImage, backgroundImage); scoreBoard = new scoreBoard(); getContentPane().add(gameBoard); getContentPane().add(scoreBoard); } public void loadImages() { sheepImage = getImage(getDocumentBase(), "sheep.png"); backgroundImage = getImage(getDocumentBase(), "bg.jpg"); } } Update guys: Alright, first of all, thank you very much for all the help you've given so far (specifically creemam and Hovercraft Full of Eels), and your persistence. You've helped me out a lot as this is incredibly important (i.e. me passing my degree). The problem now is: The program works correctly when nothing but the GameBoard class is added to the JApplet, however, when I try to add the ScoreBoard class, both Panel classes do not show on the Applet. I'm guessing this is now down to positioning? Any ideas? EDIT: Gone back to the previously asked question Hovercraft, and found it was due to the layout of the contentPane and the order at with the components were added. Thanks to all of you so much. People like you make the development community a bit of alright.

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Problem in Building mplsh-run in lshkit

- by Yijinsei

Hi guy, been trying out this for quite some time but I'm still unable to built mplsh-run from lshkit Not sure if this would help to explain my situation during the building process /tmp/cc17kth4.o: In function `lshkit::MultiProbeLshRecallTable::reset(lshkit::MultiProbeLshModel, unsigned int, double, double)': mplsh-run.cpp:(.text._ZN6lshkit24MultiProbeLshRecallTable5resetENS_18MultiProbeLshModelEjdd[lshkit::MultiProbeLshRecallTable::reset(lshkit::MultiProbeLshModel, unsigned int, double, double)]+0x230): undefined reference to `lshkit::MultiProbeLshModel::recall(double) const' /tmp/cc17kth4.o: In function `void lshkit::MultiProbeLshIndex<unsigned int>::query_recall<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, float, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&) const': mplsh-run.cpp:(.text._ZNK6lshkit18MultiProbeLshIndexIjE12query_recallINS_11TopkScannerINS_6MatrixIfE8AccessorENS_6metric5l2sqrIfEEEEEEvPKffRT_[void lshkit::MultiProbeLshIndex<unsigned int>::query_recall<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, float, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&) const]+0x2c4): undefined reference to `lshkit::MultiProbeLsh::genProbeSequence(float const*, std::vector<unsigned int, std::allocator<unsigned int> >&, unsigned int) const' /tmp/cc17kth4.o: In function `void lshkit::MultiProbeLshIndex<unsigned int>::query<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, unsigned int, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&)': mplsh-run.cpp:(.text._ZN6lshkit18MultiProbeLshIndexIjE5queryINS_11TopkScannerINS_6MatrixIfE8AccessorENS_6metric5l2sqrIfEEEEEEvPKfjRT_[void lshkit::MultiProbeLshIndex<unsigned int>::query<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, unsigned int, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&)]+0x4a): undefined reference to `lshkit::MultiProbeLsh::genProbeSequence(float const*, std::vector<unsigned int, std::allocator<unsigned int> >&, unsigned int) const' collect2: ld returned 1 exit status the command that i used to built mplsh-run is g++ -I./lshkit/include -L/usr/lib -lm -lgsl -lgslcblas -lboost_program_options-mt mplsh-run.cpp Do you guys have any clue on how I could solve this?

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Dependency Injection into your Singleton

- by Langali

I have a singleton that has a spring injected Dao (simplified below): public class MyService<T> implements Service<T> { private final Map<String, T> objects; private static MyService instance; MyDao myDao; public void set MyDao(MyDao myDao) { this. myDao = myDao; } private MyService() { this.objects = Collections.synchronizedMap(new HashMap<String, T>()); // start a background thread that runs for ever } public static synchronized MyService getInstance() { if(instance == null) { instance = new MyService(); } return instance; } public void doSomething() { myDao.persist(objects); } } My spring config will probably look like this: <bean id="service" class="MyService" factory-method="getInstance"/> But this will instantiate the MyService during startup. Is there a programmatic way to do a dependency injection of MyDao into MyService, but not have spring manage the MyService? Basically I want to be able to do this from my code: MyService.getInstance().doSomething(); while having spring inject the MyDao for me.

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Measuring the performance of classification algorithm

- by Silver Dragon

I've got a classification problem in my hand, which I'd like to address with a machine learning algorithm ( Bayes, or Markovian probably, the question is independent on the classifier to be used). Given a number of training instances, I'm looking for a way to measure the performance of an implemented classificator, with taking data overfitting problem into account. That is: given N[1..100] training samples, if I run the training algorithm on every one of the samples, and use this very same samples to measure fitness, it might stuck into a data overfitting problem -the classifier will know the exact answers for the training instances, without having much predictive power, rendering the fitness results useless. An obvious solution would be seperating the hand-tagged samples into training, and test samples; and I'd like to learn about methods selecting the statistically significant samples for training. White papers, book pointers, and PDFs much appreciated!

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c# Delegates, Events and Lambda Expr for new students

- by MarkP

I've been asked by my pointy haired boss to educate our new co-ops (interns) in the ways of C#. I have roughly ~30mins to cover the topics of Delegates, Events and Lambda Expressions. The time restriction is rather tight and the topics are broad. Since I'm not a C# guru, I would like some hints and pointers. Since my time is short, what points should I cover with respect to the three topics listed above? What are some good Do's and Dont's when using those three things? I might have time for a short Lambda Expr demo. What is the most common use of LExpr (probably a Select().Where() statement on an enumerable??) that I could demo? Thanks. EDIT: The students have working knowledge of C++ and Java.

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ReaderWriterLockSlim and Pulse/Wait

- by Jono

Is there an equivalent of Monitor.Pulse and Monitor.Wait that I can use in conjunction with a ReaderWriterLockSlim? I have a class where I've encapsulated multi-threaded access to an underlying queue. To enqueue something, I acquire a lock that protects the underlying queue (and a couple of other objects) then add the item and Monitor.Pulse the locked object to signal that something was added to the queue. public void Enqueue(ITask task) { lock (mutex) { underlying.Enqueue(task); Monitor.Pulse(mutex); } } On the other end of the queue, I have a single background thread that continuously processes messages as they arrive on the queue. It uses Monitor.Wait when there are no items in the queue, to avoid unnecessary polling. (I consider this to be good design, but any flames (within reason) are welcome if they help me learn otherwise.) private void DequeueForProcessing(object state) { while (true) { ITask task; lock (mutex) { while (underlying.Count == 0) { Monitor.Wait(mutex); } task = underlying.Dequeue(); } Process(task); } } As more operations are added to this class (requiring read-only access to the lock protected underlying), someone suggested using ReaderWriterLockSlim. I've never used the class before, and assuming it can offer some performance benefit, I'm not against it, but only if I can keep the Pulse/Wait design.

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Passing an array of structs in C

- by lelouch

I'm having trouble passing an array of structs to a function in C. I've created the struct like this in main: int main() { struct Items { char code[10]; char description[30]; int stock; }; struct Items MyItems[10]; } I then access it like: MyItems[0].stock = 10; etc. I want to pass it to a function like so: ReadFile(MyItems); The function should read the array, and be able to edit it. Then I should be able to access the same array from other functions. I've tried heaps of declarations but none of them work. e.g. void ReadFile(struct Items[10]) I've had a look around for other questions, but the thing is they're all done different, with typedefs and asterisks. My teacher hasn't taught us pointers yet, so I'd like to do it with what I know. Any ideas? :S EDIT: Salvatore's answer is working after I fixed my prototype to: void ReadFile(struct Items[9]);

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iPhone SpeakHere example produces different number of samples

- by pion

I am looking at the SpeakHere example and added the following: // Overriding the output audio route UInt32 audioRouteOverride = kAudioSessionOverrideAudioRoute_Speaker; AudioSessionSetProperty(kAudioSessionProperty_OverrideAudioRoute, sizeof (audioRouteOverride), &audioRouteOverride); assert(status == noErr); // Changing the default output route. The new output route remains in effect unless you change the audio session category. This option is available starting in iPhone OS 3.1. UInt32 doChangeDefaultRoute = 1; status = AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryDefaultToSpeaker, sizeof(doChangeDefaultRoute), &doChangeDefaultRoute); assert(status == noErr); // Enable Bluetooth. See audioRouteOverride & doChangeDefaultRoute above // http://developer.apple.com/iphone/library/documentation/Audio/Conceptual/AudioSessionProgrammingGuide/Cookbook/Cookbook.html#//apple_ref/doc/uid/TP40007875-CH6-SW2 UInt32 allowBluetoothInput = 1; status = AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryEnableBluetoothInput, sizeof(allowBluetoothInput), &allowBluetoothInput); assert(status == noErr); Also, void AQRecorder::handleInputBufferCallback(void *aqData, ... ... if (inNumPackets > 0) { NSLog(@"Number of samples = %d", inBuffer->mAudioDataByteSize/2); // print out the number of sample status = AudioFileWritePackets(aqr->mAudioFile, FALSE, inBuffer->mAudioDataByteSize, inPacketDesc, aqr->mCurrentPacket, &inNumPackets, inBuffer->mAudioData); assert(status == noErr); aqr->mCurrentPacket += inNumPackets; } ... Notice the "NSLog(@"Number of samples = %d", inBuffer-mAudioDataByteSize/2); // print out the number of sample" statement above. I am using iPhone SDK 3.1.3. I got the following results The number of samples is around 44,100 on Simulator The number of samples is around 22,000 on iPhone The number of samples is around 4,000 on iPhone using Jawbone Bluetooth I am new on this. Why did itproduce different number of samples? Thanks in advance for your help.

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Is there a way to increase the efficiency of shared_ptr by storing the reference count inside the co

- by BillyONeal

Hello everyone :) This is becoming a common pattern in my code, for when I need to manage an object that needs to be noncopyable because either A. it is "heavy" or B. it is an operating system resource, such as a critical section: class Resource; class Implementation : public boost::noncopyable { friend class Resource; HANDLE someData; Implementation(HANDLE input) : someData(input) {}; void SomeMethodThatActsOnHandle() { //Do stuff }; public: ~Implementation() { FreeHandle(someData) }; }; class Resource { boost::shared_ptr<Implementation> impl; public: Resource(int argA) explicit { HANDLE handle = SomeLegacyCApiThatMakesSomething(argA); if (handle == INVALID_HANDLE_VALUE) throw SomeTypeOfException(); impl.reset(new Implementation(handle)); }; void SomeMethodThatActsOnTheResource() { impl->SomeMethodThatActsOnTheHandle(); }; }; This way, shared_ptr takes care of the reference counting headaches, allowing Resource to be copyable, even though the underlying handle should only be closed once all references to it are destroyed. However, it seems like we could save the overhead of allocating shared_ptr's reference counts and such separately if we could move that data inside Implementation somehow, like boost's intrusive containers do. If this is making the premature optimization hackles nag some people, I actually agree that I don't need this for my current project. But I'm curious if it is possible.

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High precision event timer

- by rahul jv

#include "target.h" #include "xcp.h" #include "LocatedVars.h" #include "osek.h" /** * This task is activated every 10ms. */ long OSTICKDURATION; TASK( Task10ms ) { void XCP_FN_TYPE Xcp_CmdProcessor( void ); uint32 startTime = GetQueryPerformanceCounter(); /* Trigger DAQ for the 10ms XCP raster. */ if( XCPEVENT_DAQ_OVERLOAD & Xcp_DoDaqForEvent_10msRstr() ) { ++numDaqOverload10ms; } /* Update those variables which are modified every 10ms. */ counter16 += slope16; /* Trigger STIM for the 10ms XCP raster. */ if( enableBypass10ms ) { if( XCPEVENT_MISSING_DTO & Xcp_DoStimForEvent_10msRstr() ) { ++numMissingDto10ms; } } duration10ms = (uint32)( ( GetQueryPerformanceCounter() - startTime ) / STOPWATCH_TICKS_PER_US ); } What would be the easiest (and/or best) way to synchronise to some accurate clock to call a function at a specific time interval, with little jitter during normal circumstances, from C++? I am working on WINDOWS operating system now. The above code is for RTAS OSEK but I want to call a function at a specific time interval for windows operating system. Could anyone assist me in c++ language ??

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WPF ProgressBar - TargetParameterCountException

- by Dr_Asik

I am making my first WPF application, where I use the Youtube .NET API to upload a video to Youtube using the ResumableUploader. This ResumableUploader works asynchronously and provides an event AsyncOperationProgress to periodically report its progress percentage. I want a ProgressBar that will display this progress percentage. Here is some of the code I have for that: void BtnUpload_Click(object sender, RoutedEventArgs e) { // generate video uploader = new ResumableUploader(); uploader.AsyncOperationCompleted += OnDone; uploader.AsyncOperationProgress += OnProgress; uploader.InsertAsync(authenticator, newVideo.YouTubeEntry, new UserState()); } void OnProgress(object sender, AsyncOperationProgressEventArgs e) { Dispatcher.BeginInvoke((SendOrPostCallback)delegate { PgbUpload.Value = e.ProgressPercentage; }, DispatcherPriority.Background, null); } Where PgbUpload is my progress bar and the other identifiers are not important for the purpose of this question. When I run this, OnProgress will be hit a few times, and then I will get a TargetParameterCountException. I have tried several different syntax for invoking the method asynchronously, none of which worked. I am sure the problem is the delegate because if I comment it out, the code works fine (but the ProgressBar isn't updated of course). Thanks for any help.

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Android XML Preference issue. Can't make it persistent

- by Budius

I have a very simple activity just to show the preference fragment: public class PreferencesActivity extends Activity { Fragment frag = null; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); FragmentTransaction ft = getFragmentManager().beginTransaction(); if (frag == null) { // If not, instantiate and add it to the activity frag = new PrefsFragment(); ft.add(android.R.id.content, frag, frag.getClass().getName()); } else { // If it exists, simply attach it in order to show it ft.attach(frag); } ft.commit(); } private static class PrefsFragment extends PreferenceFragment { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); addPreferencesFromResource(R.xml.preferences); } } } and preferences.xml with persistent to true: <?xml version="1.0" encoding="utf-8"?> <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" android:enabled="true" android:persistent="true" android:title="@string/settings" > <EditTextPreference android:dialogTitle="@string/dialog_ip" android:negativeButtonText="@android:string/cancel" android:persistent="true" android:positiveButtonText="@android:string/ok" android:title="@string/ip" /> </PreferenceScreen> if I open the EditTextPreference, write something, close the dialog and open it again. The value is still there. But that's it... if I click the Back button, and enter the again on the preferences screen, I already lost what was written. If you exit the application also doesn't save. Am I missing something here? Running on: Android 4.0.3 Asus TF300

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iPhone UISlider not visible

- by John Qualis

I want to add a UISlider to my app programmatically without using the IB. I am adding a UISlider to my UIViewController using the code below. However I don't see the slider when the view comes up. What am I missing? I am using iPhone SDK 3.1.2. Appreciate any help. @synthesize slider; .... - (void)viewDidLoad { ... ... slider = [[UISlider alloc] initWithFrame: CGRectMake(0, 480 - 80, 300, 20)]; slider.minimumValue = 0.0; slider.maximumValue = 100.0; slider.tag = 0; slider.value = 50; slider.continuous = YES; slider.enabled = YES; [slider addTarget:selfaction:@selector(handleSlider:)forControlEvents:UIControlEventValueChanged]; self.view addSubview:slider]; In the .h file ... UISlider *slider; ... @property (nonatomic, retain) UISlider *slider; - (void) handleSlider:(id)sender;

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How to move from custom to transluscent NavigationBar and back? Display problems!

- by jd291

So, i got this Navigation-based App (with a custom NavigationBar - Category) and I have 2 problems here... @implementation UINavigationBar (Custom) - (void)drawRect:(CGRect)rect { UIImage *image = [UIImage imageNamed: @"bg_toolbar.png"]; [image drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)]; } @end Because of the Navigation-based App, most of the views have a height of 436px (= ScreenSize - NavigationBar height, as you probably know ;). I got one view similar to the photo app overview showing all the thumbnails, from there I push a viewcontroller containing the scroll view (like in photos app) on the stack, like so - (void)buttonPressed:(id)sender { UIButton *btn = (UIButton *)sender; PhotoSetScrollViewController *psc = [[PhotoSetScrollViewController alloc] initWithPhotoArray:photos andID:btn.tag]; [self.navigationController pushViewController:psc animated:YES]; } Problem 1: The view holding the fullscreen scrollview has a height of 480px which seems to be a problem because when poping the viewcontroller by hitting the back button, the view containing the thumbnails (height 436px) moves upward below the navigation bar. And also the Toolbar keeps showing. What could be the problem? Problem 2: How could I switch between my custom navigation bar and the standard black translucent style?

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How come drawing this line at (0,0) doesn't really draw it at (0,0)?

- by George Edison

I have this ActionScript code here: package { import flash.display.Sprite; import flash.display.LineScaleMode; import flash.display.CapsStyle; import flash.display.JointStyle; import flash.display.Shape; import flash.events.Event; public class Main extends Sprite { private var lines:Shape; public function Main():void { if (stage) init(); else addEventListener(Event.ADDED_TO_STAGE, init); } private function init(e:Event = null):void { removeEventListener(Event.ADDED_TO_STAGE, init); // entry point lines = new Shape(); addChild(lines); lines.graphics.clear(); lines.graphics.lineStyle(10, 0x000000); lines.graphics.moveTo(0, 0); lines.graphics.lineTo(stage.stageWidth, stage.stageHeight); } } } What I'm expecting this to do is to draw a line from one corner of the screen to the other... but that's not what it does. See here.

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wpf observableCollection

- by Asha

I have an ObservableCollection which is dataContext for my treeview when I try to remove an Item from ObservableCollection I will get an error that Object reference not set to an instance of an object . can you please tell me why this error is happening and what is the solution thanks EDIT 1: The code is something like : class MyClass : INotifyPropertyChanged { //my class code here } public partial class UC_myUserControl : UserControl { private ObservableCollection<MyClass> myCollection = new ObservableCollection<MyClass>(); private void UserControl_Loaded(object sender, RoutedEventArgs e) { myCollection.add(new myClass); myTreeView.DataContext = myCollection ; } private void deleteItem() { myCollection.RemoveAt(0); //after removing I get error Which I guess should be something related //to interface update but I don't know how can I solve it } } Exception Detail : System.NullReferenceException was unhandled Message="Object reference not set to an instance of an object." Source="PresentationFramework" EDIT 3: I have a style which is for my treeitem to keep the treeitems expanded <Style TargetType="TreeViewItem"> <Setter Property="IsExpanded" Value="True" /> </Style> and with commenting this part I wont get any error !!! Now I want to change my question to why having this style is causing error ?

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Dealing with multiple generics in a method call

- by thaBadDawg

I've been dealing a lot lately with abstract classes that use generics. This is all good and fine because I get a lot of utility out of these classes but now it's making for some rather ugly code down the line. For example: abstract class ClassBase<T> { T Property { get; set; } } class MyClass : ClassBase<string> { OtherClass PropertyDetail { get; set; } } This implementation isn't all that crazy, except when I want to reference the abstract class from a helper class and then I have to make a list of generics just to make reference to the implemented class, like this below. class Helper { void HelpMe<C, T>(object Value) where C : ClassBase<T>, new() { DoWork(); } } This is just a tame example, because I have some method calls where the list of where clauses end up being 5 or 6 lines long to handle all of the generic data. What I'd really like to do is class Helper { void HelpMe<C>(object Value) where C : ClassBase, new() { DoWork(); } } but it obviously won't compile. I want to reference ClassBase without having to pass it a whole array of generic classes to get the function to work, but I don't want to reference the higher level classes because there are a dozen of those. Am I the victim of my own cleverness or is there an avenue that I haven't considered yet?

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How to handle failure to release a resource which is contained in a smart pointer?

- by cj

How should an error during resource deallocation be handled, when the object representing the resource is contained in a shared pointer? Smart pointers are a useful tool to manage resources safely. Examples of such resources are memory, disk files, database connections, or network connections. // open a connection to the local HTTP port boost::shared_ptr<Socket> socket = Socket::connect("localhost:80"); In a typical scenario, the class encapsulating the resource should be noncopyable and polymorphic. A good way to support this is to provide a factory method returning a shared pointer, and declare all constructors non-public. The shared pointers can now be copied from and assigned to freely. The object is automatically destroyed when no reference to it remains, and the destructor then releases the resource. /** A TCP/IP connection. */ class Socket { public: static boost::shared_ptr<Socket> connect(const std::string& address); virtual ~Socket(); protected: Socket(const std::string& address); private: // not implemented Socket(const Socket&); Socket& operator=(const Socket&); }; But there is a problem with this approach. The destructor must not throw, so a failure to release the resource will remain undetected. A common way out of this problem is to add a public method to release the resource. class Socket { public: virtual void close(); // may throw // ... }; Unfortunately, this approach introduces another problem: Our objects may now contain resources which have already been released. This complicates the implementation of the resource class. Even worse, it makes it possible for clients of the class to use it incorrectly. The following example may seem far-fetched, but it is a common pitfall in multi-threaded code. socket->close(); // ... size_t nread = socket->read(&buffer[0], buffer.size()); // wrong use! Either we ensure that the resource is not released before the object is destroyed, thereby losing any way to deal with a failed resource deallocation. Or we provide a way to release the resource explicitly during the object's lifetime, thereby making it possible to use the resource class incorrectly. There is a way out of this dilemma. But the solution involves using a modified shared pointer class. These modifications are likely to be controversial. Typical shared pointer implementations, such as boost::shared_ptr, require that no exception be thrown when their object's destructor is called. Generally, no destructor should ever throw, so this is a reasonable requirement. These implementations also allow a custom deleter function to be specified, which is called in lieu of the destructor when no reference to the object remains. The no-throw requirement is extended to this custom deleter function. The rationale for this requirement is clear: The shared pointer's destructor must not throw. If the deleter function does not throw, nor will the shared pointer's destructor. However, the same holds for other member functions of the shared pointer which lead to resource deallocation, e.g. reset(): If resource deallocation fails, no exception can be thrown. The solution proposed here is to allow custom deleter functions to throw. This means that the modified shared pointer's destructor must catch exceptions thrown by the deleter function. On the other hand, member functions other than the destructor, e.g. reset(), shall not catch exceptions of the deleter function (and their implementation becomes somewhat more complicated). Here is the original example, using a throwing deleter function: /** A TCP/IP connection. */ class Socket { public: static SharedPtr<Socket> connect(const std::string& address); protected: Socket(const std::string& address); virtual Socket() { } private: struct Deleter; // not implemented Socket(const Socket&); Socket& operator=(const Socket&); }; struct Socket::Deleter { void operator()(Socket* socket) { // Close the connection. If an error occurs, delete the socket // and throw an exception. delete socket; } }; SharedPtr<Socket> Socket::connect(const std::string& address) { return SharedPtr<Socket>(new Socket(address), Deleter()); } We can now use reset() to free the resource explicitly. If there is still a reference to the resource in another thread or another part of the program, calling reset() will only decrement the reference count. If this is the last reference to the resource, the resource is released. If resource deallocation fails, an exception is thrown. SharedPtr<Socket> socket = Socket::connect("localhost:80"); // ... socket.reset();

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Pure virtual destructor in interface

- by ALOR

Hello all. Here is my problem. I'm making C++ dll, which extensively relies on instance object exports. So i return my actual instances as a pointers to interface through some exported factory method. Interfaces i use are purely virtual, to avoid linking problame. So i need a pure virtual destructor too, and i implemented one (with empty body, as i googled it). All compiles perfectly well, except... I can't see, if the actual destructors are called or not - because when i added some std::cout << "hello destructor"; i never get to see it. I have some explicit "delete obj", that's not the problem. Am i missing something? Is there another way to delete my object through interface?

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Rails: Ajax-enabled form without a model object

- by Caffeine Coma

I'm new to Rails and having a hard time figuring out how to create a form that submits over Ajax without having a corresponding model object. My use case is a simple form that collects an email address and sends it an email; there's nothing to be persisted, so no model. In cases where I do have a model, I've had success with form_for(@model, remote: true). I can't seem to find the right helper for the case where there is no model. I tried form_tag(named_path, remote: true) and that works, but does not use Ajax. Pointers to an example with an example with a proper controller, .html.erb and routes.rb would be really appreciated.

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