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copied!<p>It's often a bad approach to block the main thread, it will just make your app unresponsive, so why not do something like this instead?</p> <pre><code>NSArray *names; int namesIndex = 0; - (void)setup { // Insert code for adding loading animation [UIView animateWithDuration:1 animations:^{ self.view.alpha = self.view.alpha==1?0:1; } completion:^(BOOL finished) { names = @[@"John", @"Mary", @"Peter", @"Madalena"]; [self alterNames]; }]; } - (void)alterNames { if (namesIndex>=names.count) { // Insert code for removing loading animation // C. Need to wait here until all iterations above have finished. return; } NSString *name = [names objectAtIndex:namesIndex]; [UIView animateWithDuration:1 animations:^{ self.view.alpha = self.view.alpha==1?0:1; } completion:^(BOOL finished) { name = @"saf"; // A. Something that takes a few seconds to complete. // B. Need to wait here until A is completed. namesIndex++; [self alterNames]; }]; } </code></pre> <p>I have just used [UIView animation...] to make to example fully functional. Just copy and paste into your viewcontroller.m and call [self setup]; Of course, you should replace that with your code.</p> <p>Or if you want:</p> <pre><code>NSArray *names; int namesIndex = 0; - (void)setup { // Code for adding loading animation [someThing retrieve:@"foo" completion:^ { names = @[@"John", @"Mary", @"Peter", @"Madalena"]; [self alterNames]; }]; } - (void)alterNames { if (namesIndex>=names.count) { // Code for removing loading animation // C. Need to wait here until all iterations above have finished. return; } NSString *name = [names objectAtIndex:namesIndex]; [someObject lookupName:name completion:^(NSString* urlString) { name = @"saf"; // A. Something that takes a few seconds to complete. // B. Need to wait here until A is completed. namesIndex++; [self alterNames]; }]; } </code></pre> <p>Explanation:</p> <ol> <li>Start everything by calling [self setup];</li> <li>A block will be called when someThing retrieves "foo", in other words, <strong>it will wait</strong> until someThing retrieves "foo" (and the main thread won't be blocked)</li> <li>When the block is executed, alterNames is called</li> <li>If all the items in "names" have been looped through, the "looping" will stop and C could be executed.</li> <li>Else, lookup the name, and <strong>when it's done</strong>, do something with it (A), and because it happens on the main thread (You haven't said anything else), you could do B there too.</li> <li>So, <strong>when A and B is complete</strong>, jump back to 3</li> </ol> <p>See?</p> <p>Good luck with your project!</p>

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