項目中有時為了安全起見，在雙擊Home鍵，退到不活躍狀態(tài)時，需要添加模糊效果，比如下圖：

高斯模糊

要實現(xiàn)這種效果，非常簡單，只需在APPdelegate里面添加幾句代碼即可

//AppDelegate.h中添加以下屬性

@property (nonatomic,strong) UIVisualEffectView *visualEffectView;//毛玻璃效果

AppDelegate.m中

- (void)applicationWillResignActive:(UIApplication *)application {
    UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
    self.visualEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];
    self.visualEffectView.alpha = 0;
    self.visualEffectView.frame = self.window.frame;
    [self.window addSubview:self.visualEffectView];
    [UIView animateWithDuration:0.2 animations:^{
        self.visualEffectView.alpha = 1;
    }];

}


- (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.
    [UIView animateWithDuration:0.2 animations:^{
        self.visualEffectView.alpha = 0;
    } completion:^(BOOL finished) {
        [self.visualEffectView removeFromSuperview];
    }];

}

以上就是實現(xiàn)毛玻璃的全部代碼，是不是很簡單呢~~~

后續(xù)加上：經(jīng)測試這種寫法有點小問題，就是如果項目中有撥打電話的操作（系統(tǒng)彈出撥打電話的提示框）,這時彈出框下面的整個屏幕也是毛玻璃效果，這并不是我們想看到的，那怎么改呢，其實就是方法寫的位置不對，按照下面的方法寫

注意：將
- (void)applicationWillResignActive:(UIApplication *)application；
里面的代碼放進
- (void)applicationDidEnterBackground:(UIApplication *)application；
里面，兩個方法里面的代碼雖然相似，但是屬性值有所改變，要注意！！！

- (void)applicationDidEnterBackground:(UIApplication *)application {
    
    UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
    self.visualEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];
    self.visualEffectView.alpha = 1;
    self.visualEffectView.frame = self.window.frame;
    [self.window addSubview:self.visualEffectView];
    [UIView animateWithDuration:0.2 animations:^{
        self.visualEffectView.alpha = 1;
    }];

}


- (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.
    [UIView animateWithDuration:0.2 animations:^{
        self.visualEffectView.alpha = 0;
    } completion:^(BOOL finished) {
        [self.visualEffectView removeFromSuperview];
    }];

}

改成下面的方法后，上面出現(xiàn)的問題就解決了，只是可能首次進入后臺的時候不能正常顯示效果，支付寶也存在這種情況，但是基本上無傷大雅~~~