嘗試在*上呈現*（已存在）（空）

Question

我正在使用以下代碼來顯示警報控制器，但有時它會收到上述消息並且警報控制器會停止響應。這是什麼意思？固定？

+(void)showAlertFor:(UIViewController *)viewController Title:(NSString*)title WithMessage:(NSString *)message 
{ 

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Error" message:message preferredStyle:UIAlertControllerStyleAlert]; //Getting the alert view controller 
    UIAlertAction* ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) { 

    }]; 

    [alertController addAction:ok]; 

    [viewController presentViewController:alertController animated:YES completion:nil]; 
} 

Answer 1

試試這個

+(void)showAlertFor:(UIViewController *)viewController withTitle:(NSString*)title withMessage:(NSString *)message { 

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Error" message:message preferredStyle:UIAlertControllerStyleAlert]; //Getting the alert view controller 
    UIAlertAction* ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) { 

    }]; 

    [alertController addAction:ok]; 
    dispatch_async(dispatch_get_main_queue(),^{ 
    [viewController presentViewController:alertController animated:YES completion:nil]; 
    }); 
} 

調用它的主線程將解決你的問題。並確保你沒有在同一時間出示任何其他控制器。