UIAlertAction completion block not called - iOS

问题

I have an iOS app with a UIAlertController in the form of a action sheet being presented in my app when the user taps on a button.

It all works great, apart from one thing, the completion blocks don't get called for some reason.

Here is my code:

// Setup the alert information/type.
UIAlertController *action_view = [UIAlertController alertControllerWithTitle:@"Test title" message:@"test message" preferredStyle:UIAlertControllerStyleActionSheet];

// Create and add the cancel button.
UIAlertAction *cancel = [UIAlertAction actionWithTitle:@"Dismiss" style:UIAlertActionStyleCancel handler:^(UIAlertAction * action) {

    [action_view dismissViewControllerAnimated:YES completion:^{
        NSLog(@"asdhfgjk");
    }];
}];

// Add the action button to the alert.
[action_view addAction:cancel];

// Present the alert to the user.
[self presentViewController:action_view animated:YES completion:nil];

If you run that code you will see the line which dismisses the controller wont run and neither will the NSLog statement inside it. However, if you delete the NSLog and set the completion block to nil, then it does run.... why???

Thanks for your time, Dan.

回答1:

Don't attempt to dismiss the alert controller. It will be dismissed for you by the time your alert action's handler is called.

Change the "cancel" action to:

UIAlertAction *cancel = [UIAlertAction actionWithTitle:@"Dismiss" style:UIAlertActionStyleCancel handler:^(UIAlertAction * action) {
    NSLog(@"asdhfgjk");
}];

回答2:

The "cancel" action should not dismiss the view controller as mentioned by rmaddy. However, even if the "cancel" action is set to:

UIAlertAction *cancel = [UIAlertAction actionWithTitle:@"Dismiss" style:UIAlertActionStyleCancel handler:^(UIAlertAction * action) {
NSLog(@"asdhfgjk");}];

you may see the same issue with the completion block not being called. For example, implementing this (somewhat contrived) method:

- (void)dismissViewControllerAnimated:(BOOL)flag completion:(void (^)(void))completion {
   [[self presentedViewController] dismissViewControllerAnimated:flag completion:nil];
}

could also have this effect because the UIAlertController gets dismissed before the completion block is called.

来源：https://stackoverflow.com/questions/30853387/uialertaction-completion-block-not-called-ios