ios - UIAlertController 在 iOS 8.4.1 中不显示警报

Question

我已经使用

[self presentViewController:viewController animated:YES completion:nil];

在呈现的 View Controller 中，我试图呈现 UIAlertcontroller，它没有呈现也在 iOS 8.4.1 的控制台中显示警告

dispatch_async(dispatch_get_main_queue(), ^{
    UIAlertAction *extend_action = nil;
    UIAlertAction *ok_action  = nil;

    UIAlertController *controller = [UIAlertController alertControllerWithTitle:@"Call will begin"
                                                                        message:msg_str   
                                                                 preferredStyle:UIAlertControllerStyleAlert];

    extend_action = [UIAlertAction  actionWithTitle:@"Extend Time?" 
                                              style:UIAlertActionStyleDefault
                                            handler:^(UIAlertAction *action) { 
                                                 // Method.
                                            }];
    ok_action = [UIAlertAction actionWithTitle:@"Ok" 
                                         style:UIAlertActionStyleDefault                            
                                       handler:^(UIAlertAction *action) { 
                                    }];                        
    [controller addAction:extend_action];
    [controller addAction:ok_action];
    [self presentViewController:controller animated:YES completion:nil];
});

尝试在其 View 不在窗口层次结构中呈现 UIAlertController!
我得到了警告。

Answer 1

尝试在主队列上呈现它:

dispatch_async(dispatch_get_main_queue(), {
    self.presentViewController(alertController, animated: true, completion: nil)
})