在iOS中终止并再次启动应用程序时，NSNotificationCenter不会触发

Question

我有一个物流应用程序，它要求禁用屏幕录制，我不希望人们使用新的iOS-11功能来录制带有敏感数据的屏幕并将其公之于众。由于禁用屏幕录制在iOS中是不可能的，所以我尝试了一种解决方法，检测iOS11屏幕录制功能的打开或关闭。我使用了isCaptured和UIScreenCapturedDidChange通知。代码如下：

   - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  if (@available(iOS 11.0, *)) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(screenCaptureChanged) name:UIScreenCapturedDidChangeNotification object:nil];
    }

    return YES;
 }

所以逻辑是，当屏幕记录开始时，通知被触发，并且在记录发生时将黑色置于视频上的逻辑被移除，而当记录停止时，黑色被移除。当应用程序移动到后台、活动、非活动和前台场景时，这一点工作得很好。但是，当应用程序在屏幕录制仍在进行时被终止(终止)，以及当我们再次启动应用程序时屏幕录制仍在进行时，黑色不会覆盖屏幕。那么如何在选择器方法工作的情况下再次调用通知选择器呢

Answer 1

在application:didFinishLaunchingWithOptions:中检查屏幕的isCaptured属性的值，并相应地显示或隐藏覆盖视图。

UIWindow+ScreenCapture.h：

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface UIWindow (ScreenCapture)

- (void)showOrHideContentDependingOnCapturedState;
- (void)hideContent;
- (void)showContent;

@end

NS_ASSUME_NONNULL_END

UIWindow+ScreenCapture.m：

#import "UIWindow+ScreenCapture.h"

@implementation UIWindow (ScreenCapture)

- (void)showOrHideContentDependingOnCapturedState {
    if (self.screen.isCaptured) {
        [self hideContent];
    } else {
        [self showContent];
    }
}

- (void)hideContent {
    UIView *blackView = [self viewWithTag:1234];
    if (!blackView) {
        blackView = [[UIView alloc] initWithFrame:self.bounds];
    }

    blackView.tag = 1234;
    blackView.backgroundColor = UIColor.blackColor;
    blackView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;

    // This is important! If this is not set, then any new view added to
    // the window (like the root view controller's view) will be overtop of
    // `blackView`, which we don't want.
    blackView.layer.zPosition = 10000;

    [self addSubview:blackView];
}

- (void)showContent {
    [[self viewWithTag:1234] removeFromSuperview];
}

@end

AppDelegate.h：

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (nullable, strong, nonatomic) UIWindow *window;

@end

AppDelegate.m：

#import "AppDelegate.h"
#import "UIWindow+ScreenCapture.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(checkIsBeingRecorded)
                                                 name:UIScreenCapturedDidChangeNotification
                                               object:nil];
    [self.window showOrHideContentDependingOnCapturedState];

    return YES;
}

- (void)checkIsBeingRecorded {
    for (UIWindow *window in UIApplication.sharedApplication.windows) {
        [window showOrHideContentDependingOnCapturedState];
    }
}

@end