如何用按钮取消 "dispatch_get_main_queue"？

Question

我正在尝试为任务调用编写代码 API，这里的问题是屏幕何时显示仍在后台运行的任务：

[[JPNetworkingManager sharedManager] getSnapNSendsForLetterWithID:letterID withIsArchived:isArchived completionHandler:^(NSArray *snapNSends, NSError *error) {
        dispatch_async(dispatch_get_main_queue(), ^{
         //do my code
        });
}];

那么我该如何取消这个任务呢？谢谢！

Answer 1

你需要确保这个apireturns完成一次

[[JPNetworkingManager sharedManager] getSnapNSendsForLetterWithID

或者这样做

var once = true 

[[JPNetworkingManager sharedManager] getSnapNSendsForLetterWithID:letterID withIsArchived:isArchived completionHandler:^(NSArray *snapNSends, NSError *error) {

    if once { 

       dispatch_async(dispatch_get_main_queue(), ^{
            //do my code
       }); 

       once = false
    }
}

如何用按钮取消 "dispatch_get_main_queue"？

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