似乎目前所见这样的效果都是在金融类App中，毕竟钱真的很重要😳。在此尝试一下，反正闲着也是闲着（？）。

可知双击Home键或者应用退到后台的时候，都会经历以下方法：

- (void)applicationWillResignActive:(UIApplication *)application { }

所以在这里添加毛玻璃效果，并且在

- (void)applicationDidBecomeActive:(UIApplication *)application { }

方法中删除此效果。

步骤在此

• 获取当前VC

- (UIViewController *)currentVC {
    
    UIViewController *currentVC = nil;
    
    if (self.window.windowLevel != UIWindowLevelNormal) {
        
        NSArray *windows = [[UIApplication sharedApplication] windows];
        for (UIWindow *window in windows) {
            
            if (window.windowLevel == UIWindowLevelNormal) {
                
                self.window = window;
                break;
            }
        }
    }
    
    UIView *frontView = [[self.window subviews] lastObject];
    id nextResponder = [frontView nextResponder];
    
    if ([nextResponder isKindOfClass:[UIViewController class]]) {
        
        currentVC = nextResponder;
    } else {
        
        currentVC = self.window.rootViewController;
    }
    
    return currentVC;
}

• 截取当前视图

- (UIImage *)snapShot:(UIView *)view {
    
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, YES, 0);
    [view drawViewHierarchyInRect:view.bounds afterScreenUpdates:YES];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return image;
}

• 添加毛玻璃效果

- (void)applicationWillResignActive:(UIApplication *)application {
    
    NSLog(@"applicationWillResignActive");
    
    // 毛玻璃效果
    UIView *view = [[UIView alloc] initWithFrame:[UIScreen mainScreen].bounds];
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:[UIScreen mainScreen].bounds];
    UIViewController *vc = [self currentVC];
    imageView.image = [self snapShot:vc.view];
    
    UIBlurEffect *blur = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
    UIVisualEffectView *effectView = [[UIVisualEffectView alloc] initWithEffect:blur];
    effectView.frame = [UIScreen mainScreen].bounds;
    
    [imageView addSubview:effectView];
    view.tag = 1000;
    [view addSubview:imageView];
    [self.window addSubview:view];
}

• 在应用DidBecomeActive时去除效果

- (void)applicationDidBecomeActive:(UIApplication *)application {
    
    for (UIWindow *window in [[UIApplication sharedApplication] windows]) {
        
        if (window.windowLevel == UIWindowLevelNormal) {
            
            UIView *view = [window viewWithTag:1000];
            [view removeFromSuperview];
        }
    }
}

以上。