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PONSTimer as a timeout mechanism
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  1. PONSTimer as a timeout mechanism
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    copied!<p>I'm pretty sure this is really simple, and I'm just missing something obvious. I have an app that needs to download data from a web service for display in a UITableView, and I want to display a UIAlertView if the operation takes more than X seconds to complete. So this is what I've got (simplified for brevity):</p> <p><strong>MyViewController.h</strong></p> <pre><code>@interface MyViewController : UIViewController &lt;UITableViewDelegate, UITableViewDataSource&gt; { NSTimer *timer; } @property (nonatomic, retain) NSTimer *timer; </code></pre> <p><strong>MyViewController.m</strong></p> <pre><code>@implementation MyViewController @synthesize timer; - (void)viewDidLoad { timer = [NSTimer scheduledTimerWithTimeInterval:20 target:self selector:@selector(initializationTimedOut:) userInfo:nil repeats:NO]; [self doSomethingThatTakesALongTime]; [timer invalidate]; } - (void)doSomethingThatTakesALongTime { sleep(30); // for testing only // web service calls etc. go here } - (void)initializationTimedOut:(NSTimer *)theTimer { // show the alert view } </code></pre> <p>My problem is that I'm expecting the <code>[self doSomethingThatTakesALongTime]</code> call to block while the timer keeps counting, and I'm thinking that if it finishes before the timer is done counting down, it will return control of the thread to <code>viewDidLoad</code> where <code>[timer invalidate]</code> will proceed to cancel the timer. Obviously my understanding of how timers/threads work is flawed here because the way the code is written, the timer never goes off. However, if I remove the <code>[timer invalidate]</code>, it does.</p>
 

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