Question

我正在编写一种方法来使用来自Web服务的数据。我在一个类（公共类）中编写了这个方法，所以我可以在任何viewController中使用这个类来使用数据。在这个方法中，我检查互联网连接。如果发生某些故障，我想显示带有错误描述的警报。这是我方法中的代码：

 dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^{

        mainSession = [NSURLSession sharedSession];
        mainDataTask = [mainSession dataTaskWithRequest:MainRequest completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

            if (error) {
                UIAlertController *alertOne = [UIAlertController alertControllerWithTitle:@"Something Wrong!" message:[error description] preferredStyle:UIAlertControllerStyleAlert];
                // I want to show alert here 
            }
        }];

    });

这个方法在我的公共类（NSObject）中。如果连接有问题，我想在此块中显示错误。我怎么能这样做？

Answer 1

你的NSObject类中的

#import <UIKit/UIKit.h>

然后你可以使用UIAlertController。

UIAlertController *alertController=[UIAlertController alertControllerWithTitle:@"Title" message:nil preferredStyle:UIAlertControllerStyleAlert];
//...
id rootViewController=[UIApplication sharedApplication].delegate.window.rootViewController;
if([rootViewController isKindOfClass:[UINavigationController class]])
{
   rootViewController=[((UINavigationController *)rootViewController).viewControllers objectAtIndex:0];
}
[rootViewController presentViewController:alertController animated:YES completion:nil];

Answer 2

在主队列中执行AlertController声明，如下所示

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^{

        mainSession = [NSURLSession sharedSession];
        mainDataTask = [mainSession dataTaskWithRequest:MainRequest completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

            if (error) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    UIAlertController *alertOne = [UIAlertController alertControllerWithTitle:@"Something Wrong!" message:[error description] preferredStyle:UIAlertControllerStyleAlert];
                    // I want to show alert here
                }); 
            }
        }];

    });

Answer 3

使用以下代码。我希望它会对你有所帮助

//调用方法

        [self showMessage:@"There is no internet connection for this device"
           withTitle:@"Error"];

//写方法如

#pragma mark
#pragma mark -- UIAlertView Method
-(void)showMessage:(NSString*)message withTitle:(NSString *)title{
dispatch_async(dispatch_get_main_queue(), ^{
    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
    [alertController addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

    }]];

    [[[[UIApplication sharedApplication] keyWindow] rootViewController] presentViewController:alertController animated:YES completion:^{
    }];
});
}

Answer 4

如果您没有View Controller，如何使用UIAlertController呈现警报视图。 Description

是的，您只能在UIViewController类中使用UIAlertController。那么我们怎样才能在NSObject类中完成它。如果您看到上面给出的描述链接，您将得到答案。要总结以上描述：在当前窗口上方创建一个新窗口。这个新窗口将是我们显示警报的viewController。因此，使用此viewController，您可以调用方法[presentViewController: animated: completion:]。

dispatch_async(dispatch_get_main_queue(), ^{

                    UIWindow* window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];

                    window.rootViewController = [UIViewController new];

                    window.windowLevel = UIWindowLevelAlert + 1;



                    NSString *msg=@“Your mssg";

                    UIAlertController* alertCtrl = [UIAlertController alertControllerWithTitle:@“Title" message:msg preferredStyle:UIAlertControllerStyleAlert];



                    [alertCtrl addAction:[UIAlertAction actionWithTitle:NSLocalizedString(@"Yes",@"Generic confirm") style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {

                        // do your stuff

                        // very important to hide the window afterwards.


                        window.hidden = YES;

                    }]];

                    UIAlertAction *cancelAction= [UIAlertAction actionWithTitle:@"cancel" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

                         window.hidden = YES; 

                    }];

                    [alertCtrl addAction:cancelAction];

                    //http://stackoverflow.com/questions/25260290/makekeywindow-vs-makekeyandvisible

                    [window makeKeyAndVisible]; //The makeKeyAndVisible message makes a window key, and moves it to be in front of any other windows on its level

                    [window.rootViewController presentViewController:alertCtrl animated:YES completion:nil];

                });

Answer 5

使用下面的代码从NSObject类中展示UIAlertController。

[[[UIApplication sharedApplication] delegate].window.rootViewController presentViewController:alertViewController animated:true completion:nil];

如何在iOS 9中的NSObject类中显示UIAlertController？

5 个答案: