ios - 如果我将我的应用程序移到后台然后在 iOS 中进入前台，则呈现的 View Controller 会被解散

Question

当用户将应用程序移至后台时，我需要用黑色布局覆盖屏幕 applicationDidEnterBackground 为了维护屏幕上某些敏感数据的隐私。因此，为此我使用 AppDelegate 函数在背景中呈现黑色，然后在前景 时通过将其关闭来移除它applicationDidEnterBackground .代码是:

#import "AppDelegate.h"

@interface AppDelegate ()

@end

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    return YES;
}

- (void)applicationDidEnterBackground:(UIApplication *)application {
    UIViewController *blankViewController = [UIViewController new];
    blankViewController.view.backgroundColor = [UIColor blackColor];
    [self.window makeKeyAndVisible];
    [self.window.rootViewController presentViewController:blankViewController animated:NO completion:NULL];
}


- (void)applicationWillEnterForeground:(UIApplication *)application {
    [self.window.rootViewController dismissViewControllerAnimated:false completion:nil];
}

@end

现在在我的应用程序中一切正常，但在一个屏幕上我显示了 ViewContollerB 使用按钮单击: [self presentViewController:webview animated:YES completion:nil];应用程序在移动到背景时通常会被黑色覆盖，但是当我在此之后将应用程序带到前台时，会出现 ViewContollerB 也被解雇了。如何防止我呈现的 ViewController 从后台消失？

Answer 1

创建一个名为 OverLayViewController 的新 'UIViewController'并将其加载applicationDidEnterBackground 方法

- (void)applicationDidEnterBackground:(UIApplication *)application {
    OverLayViewController *blankViewController = [OverLayViewController new];
    blankViewController.view.backgroundColor = [UIColor blackColor];
    [self.window makeKeyAndVisible];
    
    UIViewController *rvc = self.window.rootViewController;
    UIViewController *pvc = rvc.presentedViewController;  // you may need to loop through presentedViewControllers if you have more than one
    if(pvc != nil) {
        [pvc presentViewController: blankViewController animated: NO completion:nil];
    }
    else{
        [self.window.rootViewController presentViewController: blankViewController animated: NO completion:nil];
    }
}

- (void)applicationWillEnterForeground:(UIApplication *)application {
    UIViewController *test = [self topViewController];
    if ([test isKindOfClass:[OverLayViewController class]]) {
           [test dismissViewControllerAnimated:false completion:nil];
    }
}


- (UIViewController*)topViewController {
    return [self topViewControllerWithRootViewController:[UIApplication sharedApplication].keyWindow.rootViewController];
}

-(UIViewController*)topViewControllerWithRootViewController:(UIViewController*)rootViewController {
    if ([rootViewController isKindOfClass:[UITabBarController class]]) {
        UITabBarController* tabBarController = (UITabBarController*)rootViewController;
        return [self topViewControllerWithRootViewController:tabBarController.selectedViewController];
    } else if ([rootViewController isKindOfClass:[UINavigationController class]]) {
        UINavigationController* navigationController = (UINavigationController*)rootViewController;
        return [self topViewControllerWithRootViewController:navigationController.visibleViewController];
    } else if (rootViewController.presentedViewController) {
        UIViewController* presentedViewController = rootViewController.presentedViewController;
        return [self topViewControllerWithRootViewController:presentedViewController];
    } else {
        return rootViewController;
    }
}

在这种情况下， dismissViewContoller代码不适用于您的 webview。