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POCan't Find Cocoa GUI Thread in C++ Application w/ Objective-C++ GUI
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  1. POCan't Find Cocoa GUI Thread in C++ Application w/ Objective-C++ GUI
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    copied!<p>I have a multi-posix-threaded Linux C++ application without a GUI that I want to be able to use the occasional Cocoa control in, namely the file upload/download dialogs and the alert.</p> <p>I'm far from an expert with Cocoa, but was able to build a few Objective-C++ test/demo apps that worked as intended.</p> <p>Now that I've integrated the Cocoa code into my application, it seems that I'm having trouble posting things to the main GUI thread. Maybe I didn't do what I needed to do to create one, I'm really not sure. Here's what I have in my .mm file:</p> <pre><code>#ifdef MACOS @interface CocoaInterface : NSObject { } - (id) init; - (void) ShowFileUploadDialog; - (void) ShowFileDownloadDialog; @end @implementation CocoaInterface - (id) init { cout &lt;&lt; "Creating NSAutoreleasePool" &lt;&lt; endl; NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init]; cout &lt;&lt; "Creating NSApplication" &lt;&lt; endl; NSApplication* app = [[NSApplication alloc] init]; cout &lt;&lt; "Calling NSApplication::finishLaunching" &lt;&lt; endl; [app finishLaunching]; [super init]; return self; } - (void) ShowFileUploadDialog { cout &lt;&lt; "Entering ShowFileUploadDialog" &lt;&lt; endl; if ([NSThread isMainThread]) { // Show file dialog cout &lt;&lt; "Calling NSRunAlertPanel" &lt;&lt; endl; NSRunAlertPanel(@"This is a test", @"Does it work?", @"Yes", @"No", @""); } else { //NSRunAlertPanel(@"This is a test", @"Does it work?", @"Yes", @"No", @""); cout &lt;&lt; "Redirecting ShowFileUploadDialog call to main thread." &lt;&lt; endl; [self performSelectorOnMainThread:@selector(ShowFileUploadDialog) withObject:nil waitUntilDone:YES]; } } - (void) ShowFileDownloadDialog { cout &lt;&lt; "Entering ShowFileDownloadDialog" &lt;&lt; endl; if ([NSThread isMainThread]) { // Show file dialog cout &lt;&lt; "Calling NSRunAlertPanel" &lt;&lt; endl; NSRunAlertPanel(@"This is a test", @"Does it work?", @"Yes", @"No", @""); } else { //NSRunAlertPanel(@"This is a test", @"Does it work?", @"Yes", @"No", @""); cout &lt;&lt; "Redirecting ShowFileDownloadDialog call to main thread." &lt;&lt; endl; [self performSelectorOnMainThread:@selector(ShowFileDownloadDialog) withObject:nil waitUntilDone:YES]; } } @end #endif </code></pre> <p>I call this from the code I have in the various threads I have processing incoming network messages:</p> <pre><code>cout &lt;&lt; "Creating CocoaInterface." &lt;&lt; endl; CocoaInterface* interface = [[CocoaInterface alloc] init]; cout &lt;&lt; "Calling CocoaInterface::ShowFileDownloadDialog." &lt;&lt; endl; [interface ShowFileDownloadDialog]; </code></pre> <p>This hangs on trying to perform the selector -- as if it can never actually find the main thread. A backtrace in GDB shows me waiting on a semaphore forever.</p> <p>When I uncomment the NSRunAlertPanel call before the performSelectorOnMainThread call, I get a white block in the shape of the dialog, but it doesn't fully draw or process any messages, presumably because it's not on the main GUI thread.</p> <p>It seems that I don't have a proper GUI thread or just can't get to it from where I am. I suspect that I've missed something in initialization. Any suggestions?</p>
 

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