Hello, I'm using Matt Gemmell's NSImage category to create an NSImage from a QuickLook thumbnail, which uses QLThumbnailImageCreate() to generate the thumbnail image.
My app also makes use of the new 10.6 QuickLook functionality to bring up a QuickLook panel for certain file previews. However, there seems to be a strange (though apparently minor) conflict here. QLThumbnailImageCreate() works absolutely fine _until_ a QuickLook panel is created. After that, even if the QuickLook panel is ordered out, calling QLThumbnailImageCreate() (on the main thread) generates the following error message on the console: [QL] Asking to compute a thumbnail in main thread is potentially blocking the user interface I've created a small demo app, showing the problem, here: http://www.literatureandlatte.com/misc/QLWarningTest.zip But you could equally see the problem by placing the following code somewhere, such as as in -awakeFromNib: NSURL *fileURL = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"SomeFile" ofType:@"type"]]; NSDictionary *dict = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:(NSString *)kQLThumbnailOptionIconModeKey]; // Call thumbnail image create once - there will be no warning. NSLog (@"1"); CGImageRef ref = QLThumbnailImageCreate(kCFAllocatorDefault, (CFURLRef)fileURL, CGSizeMake(48, 48), (CFDictionaryRef)dict); // Call it again - and again no warning. NSLog (@"2"); ref = QLThumbnailImageCreate(kCFAllocatorDefault, (CFURLRef)fileURL, CGSizeMake(48, 48), (CFDictionaryRef)dict); // Order the QL panel front. [[QLPreviewPanel sharedPreviewPanel] makeKeyAndOrderFront:nil]; // Now when we try to create a thumbnail, there will be a warning. NSLog (@"3"); ref = QLThumbnailImageCreate(kCFAllocatorDefault, (CFURLRef)fileURL, CGSizeMake(48, 48), (CFDictionaryRef)dict); The console output will be: 1 2 3 [QL] Asking to compute a thumbnail in main thread is potentially blocking the user interface So, my question is, does anyone know why this warning gets generated by QLThumbnailImageCreate after a QuickLook panel has been created in an application? The docs say that QLThumbnailImageCreate should "generally" be called from a background thread, but do not say that it must be. Is this function not supposed to be placed in the main thread after all? I'm not sure how I would really improve on Matt Gemmell's NSImage category (included in the demo app above, and which I seem to remember reading on his site has already had someone at Apple tweak it), as I'm not really sure why the thumbnail creation for an image about to be placed in the main interface should have to go in a different thread. Many thanks in advance and all the best, Keith _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
