如何在app delegate（obj-c）中添加UIAlertController

Question

这是我在弃用UIAlertView之前使用的代码：

//OLD UIALERTVIEW
- (void)applicationDidBecomeActive:(UIApplication *)application {
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.

    // check to see if newer version exists to alert the user
    BOOL updateAvailable = NO;
    NSDictionary *updateDictionary = [NSDictionary dictionaryWithContentsOfURL:[NSURL URLWithString:@"PLIST_URL_HERE"]];
    NSArray *items = [updateDictionary objectForKey:@"items"];
    NSDictionary *itemDict = [items lastObject];
    NSDictionary *metaData = [itemDict objectForKey:@"metadata"];
    NSString *newversion = [metaData  valueForKey:@"bundle-version"];
    NSString *currentversion = [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleShortVersionString"];

    //updateAvailable = [newversion compare:currentversion options:NSNumericSearch] == NSOrderedDescending; //default code
    updateAvailable = [@"1.3" compare:currentversion options:NSNumericSearch] == NSOrderedDescending; //force update
    //updateAvailable = [@"1.1" compare:currentversion options:NSNumericSearch] == NSOrderedDescending; //force no update

    if (updateAvailable) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"UPDATE AVAILABLE" message:@"Click OK to update the application to the latest version" delegate:self cancelButtonTitle:@"Later" otherButtonTitles:@"OK", nil];
        [alert show];
    }
}


-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    if (buttonIndex != [alertView cancelButtonIndex]) {
        // point to the pList on dropbox to install the
        [[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"PLIST_URL_HERE"]];
        exit(0);

我正在尝试更新它以使用UIAlertController。 下面是我正在使用的代码

//NEW UIACTIONCONTROLLER
- (void)applicationDidBecomeActive:(UIApplication *)application {
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.

    // check to see if newer version exists to alert the user
    BOOL updateAvailable = NO;
    NSDictionary *updateDictionary = [NSDictionary dictionaryWithContentsOfURL:[NSURL URLWithString:@"PLIST_URL_HERE"]];
    NSArray *items = [updateDictionary objectForKey:@"items"];
    NSDictionary *itemDict = [items lastObject];
    NSDictionary *metaData = [itemDict objectForKey:@"metadata"];
    NSString *newversion = [metaData  valueForKey:@"bundle-version"];
    NSString *currentversion = [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleShortVersionString"];

    //updateAvailable = [newversion compare:currentversion options:NSNumericSearch] == NSOrderedDescending; //default code
    updateAvailable = [@"1.3" compare:currentversion options:NSNumericSearch] == NSOrderedDescending; //force update
    //updateAvailable = [@"1.1" compare:currentversion options:NSNumericSearch] == NSOrderedDescending; //force no update

    if (updateAvailable) {
        UIAlertController * alert=   [UIAlertController alertControllerWithTitle:@"UPDATE AVAILABLE" message:@"Click OK to update the application to the latest version" preferredStyle:UIAlertControllerStyleAlert];

        UIAlertAction *ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
        [[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"PLIST_URL_HERE"]];
        exit(0);
        }];

        UIAlertAction *cancel = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:nil];

        [alert addAction:ok];
        [alert addAction:cancel];

        [self presentViewController:alert animated:YES completion:nil];
    }
}

问题是这段代码：

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

给我这个错误：

/Users/liz/Desktop/CactusQueuesGit/CactusQueue/AppDelegate.m:154:15：'AppDelegate'没有可见的@interface声明选择器'presentViewController：animated：completion：'

我可以将该代码放在viewDidLoad但我不希望每次用户转到TableView时都会弹出警报。 我只想在应用程序打开时加载它。

我该怎么做呢？

Answer 1

根据Apple文档 ， UIAlertController就像任何另一个需要视图控制器作为基础的视图控制器一样。

要从AppDelegate呈现UIAlertController ，您可以创建一个临时窗口，其中包含一个空视图控制器并显示在其上。 像这样的东西：

self.alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
self.alertWindow.rootViewController = [[UIViewController alloc] init];
self.alertWindow.windowLevel = UIWindowLevelAlert + 1;
[self.alertWindow makeKeyAndVisible];
[self.alertWindow.rootViewController presentViewController:alertControl animated:YES completion:nil];

一旦警报被取消，该窗口将自动从内存中取出。

如果已经初始化并添加到视图层次结构中，您还可以在rootViewController上显示警报。

我希望你知道为什么你现在得到这个错误。 从技术上讲， AppDelegate不是视图控制器，因此不响应presentViewController:animated:completion:方法。

Answer 2

  let navigationController = application.windows[0].rootViewController as UINavigationController

            let activeViewCont = navigationController.visibleViewController

            activeViewCont.presentViewController(alertController, animated: true, completion: nil)