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POperformSelectorOnMainThread results in "unrecognized selector sent to instance"
 

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  1. POperformSelectorOnMainThread results in "unrecognized selector sent to instance"
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    <p>Firstly thanks in advance for your time looking at this question.</p> <p>I'm trying to create a very simple UIViewController example, where I load the data in a thread. The thread is getting called but from that thread, I can't get back to the main thread. The test case below is extremely simple, I create a View based application in XCode and just added the NSOperationQueue code. Hopefully someone can quickly spot my schoolboy error :)</p> <p>The delegate is very simple, .h is:</p> <pre><code>#import&lt;UIKit/UIKit.h&gt; @class ViewbasedViewController; @interface ViewbasedAppDelegate : NSObject &lt;UIApplicationDelegate&gt; { UIWindow *window; ViewbasedViewController *viewController; } @property (nonatomic, retain) IBOutlet UIWindow *window; @property (nonatomic, retain) IBOutlet ViewbasedViewController *viewController; @end </code></pre> <p>And the .m is equally simple:</p> <pre><code>#import "ViewbasedAppDelegate.h" #import "ViewbasedViewController.h" @implementation ViewbasedAppDelegate @synthesize window; @synthesize viewController; #pragma mark - #pragma mark Application lifecycle - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { // Override point for customization after application launch. // Set the view controller as the window's root view controller and display. self.window.rootViewController = self.viewController; [self.window makeKeyAndVisible]; return YES; } </code></pre> <p>Now to the question. I want to run a thread when the view is loaded. I've defined an NSOperationQueue in my viewcontroller.h file:</p> <pre><code>@interface ViewbasedViewController : UIViewController { NSOperationQueue *folderQueue; } </code></pre> <p>And in my view controller.m, I want to run some code in a thread once the view is loaded. So inside viewDidLoad I add an operation to a queue: </p> <pre><code>- (void)viewDidLoad { [super viewDidLoad]; // create a thread and run it folderQueue = [[NSOperationQueue alloc] init]; folderQueue.maxConcurrentOperationCount = 1; NSLog(@"about to run thread"); [folderQueue addOperation:[[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(MyThreadedCode) object:nil] autorelease]]; </code></pre> <p>}</p> <p>The function "MyThreadedCode" gets called ok, I can see the debug in the console.</p> <pre><code>-(void)MyThreadedCode { NSLog(@"Start of thread"); [self performSelectorOnMainThread:@selector(reloadMyData) withObject:nil WaitUntilDone:YES]; // [self reloadMyData]; NSLog(@"CALLED REFRESH"); } -(void)reloadMyData { NSLog(@"Request to reloadData"); } </code></pre> <p>BUT...if, from my thread, I try and call a selector on the main thread (for instance I may want to reload data in a tableview), I get an exception. I only get this if I run it using performanceSelectorOnMainThread. If I run </p> <pre><code>[self reloadMyData]; </code></pre> <p>The console looks good:</p> <pre><code>[Session started at 2011-09-06 13:56:50 +0100.] 2011-09-06 13:56:52.258 Viewbased[1618:207] about to run thread 2011-09-06 13:56:52.266 Viewbased[1618:5d03] Start of thread 2011-09-06 13:56:52.270 Viewbased[1618:5d03] Request to reloadData 2011-09-06 13:56:52.272 Viewbased[1618:5d03] CALLED REFRESH </code></pre> <p>If I use </p> <pre><code>[self performSelectorOnMainThread:@selector(reloadMyData) withObject:nil WaitUntilDone:YES]; </code></pre> <p>I get an unrecognized selector:</p> <pre><code>[Session started at 2011-09-06 13:29:14 +0100.] 2011-09-06 13:29:26.216 Viewbased[1581:207] about to run thread 2011-09-06 13:29:26.224 Viewbased[1581:5d03] Start of thread 2011-09-06 13:29:26.228 Viewbased[1581:5d03] -[ViewbasedViewController performSelectorOnMainThread:withObject:WaitUntilDone:]: unrecognized selector sent to instance 0x4e43060 2011-09-06 13:29:26.235 Viewbased[1581:5d03] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewbasedViewController performSelectorOnMainThread:withObject:WaitUntilDone:]: unrecognized selector sent to instance 0x4e43060' *** Call stack at first throw: ( 0 CoreFoundation 0x00eab5a9 __exceptionPreprocess + 185 1 libobjc.A.dylib 0x00cda313 objc_exception_throw + 44 2 CoreFoundation 0x00ead0bb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187 3 CoreFoundation 0x00e1c966 ___forwarding___ + 966 4 CoreFoundation 0x00e1c522 _CF_forwarding_prep_0 + 50 5 Viewbased 0x000024c3 -[ViewbasedViewController MyThreadedCode] + 78 6 CoreFoundation 0x00e1bc7d __invoking___ + 29 7 CoreFoundation 0x00e1bb51 -[NSInvocation invoke] + 145 8 Foundation 0x000d9495 -[NSInvocationOperation main] + 51 9 Foundation 0x00047b76 -[__NSOperationInternal start] + 747 10 Foundation 0x000477ca ____startOperations_block_invoke_2 + 106 11 libdispatch_sim.dylib 0x01628289 _dispatch_call_block_and_release + 16 12 libdispatch_sim.dylib 0x0162b58a _dispatch_worker_thread2 + 252 13 libSystem.B.dylib 0x9557e781 _pthread_wqthread + 390 14 libSystem.B.dylib 0x9557e5c6 start_wqthread + 30 ) terminate called after throwing an instance of 'NSException' </code></pre> <p>I'm sure its something stupid I've got wrong but I can't see it for looking!!</p>
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