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POWhy NSOperationQueue is faster than GCD or performSelectorOnMainThread when they process a large number of tasks on the main Thread?
 

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  1. POWhy NSOperationQueue is faster than GCD or performSelectorOnMainThread when they process a large number of tasks on the main Thread?
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    <p>for example, i have 100 times the for loop. and need to update UIImageView,and the last 2 method is same slowly. why? what is the different between they?</p> <pre><code>//fastest [[NSOperationQueue mainQueue] addOperationWithBlock:^{ [btnThumb setImage:[UIImage imageWithData:data] forState:UIControlStateNormal]; [scrollView addSubview:btnThumb]; }]; //slowly dispatch_async(dispatch_get_main_queue(), ^ { [btnThumb setImage:[UIImage imageWithData:data] forState:UIControlStateNormal]; [scrollView addSubview:btnThumb]; }); //slowly [btnThumb setImage:[UIImage imageWithData:data] forState:UIControlStateNormal]; [self performSelectorOnMainThread:@selector(testMethod:) withObject:[NSArray arrayWithObjects:scrollView, btnThumb, nil] waitUntilDone:NO]; -(void) testMethod:(NSArray*)objs { UIScrollView *scroll = [objs objectAtIndex:0]; UIButton *btn = [objs lastObject]; [scroll addSubview:btn]; } </code></pre>
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    1. US不及格的程序员-八神
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    1. COYes, how are you measuring the speed differences, and what differences are you seeing?
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      1. USJesse Rusak
    2. COthe fastest situation is all images display very fast,one by one showed. But the other situation is They are displayed together at the same time, rather than a one of the concurrently displayed.
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      1. POWhy NSOperationQueue is faster than GCD or performSelectorOnMainThread when they process a large number of tasks on the main Thread?
      1. US不及格的程序员-八神
    3. COBy the way, if you're trying to animate the changing of images to animate a button, you might also want to benchmark the `UIImageView` [image animation methods](http://developer.apple.com/library/ios/documentation/uikit/reference/UIImageView_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40006889-CH3-SW8). It might be better optimized for animation of changing of images. Also caching of your images (e.g. `NSCache`) might have real impact, as `imageWithData` is expensive. If you want to discuss optimal ways to animate switching of images, that might be worthy of its own question.
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      1. USRob
 

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