Objective-C, cancel a dispatch queue using UI event

Question

Scenario:

• User taps a button asking for some kind of modification on address book.
• A method is called to start this modification and an alert view is

Answer 1

Try to apply the following code sample to your situation:

__block UIView * tempView = [[UIView alloc] initWithFrame:CGRectMake(50, 100, 220, 30)];
[tempView setBackgroundColor:[UIColor grayColor]];
[self.view addSubview:tempView];
[tempView release];

__block BOOL cancel = NO;
//点击之后就会开始执行这个方法
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
    int i = 0;
    while (i < 1000000000 && cancel == NO) {
        i++;
    }
    NSLog(@"Task end: i = %d", i);
    //这个不会执行，因为在之前，gcd task已经结束
    [tempView removeFromSuperview];
});

//1s 之后执行这个方法
double delayInSeconds = 1.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    NSLog(@"A GCD Task Start");
    cancel = YES;
    [tempView setBackgroundColor:[UIColor blackColor]];
});