iOS SDK 自 iOS8.0 開始提供了背景虛化的相關 api，簡單的幾句程式碼就可以實現虛化背景，毛玻璃特效，有需要的趕緊試試！

    UIBlurEffect *blur = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];

    UIVisualEffectView *effectview = [[UIVisualEffectView alloc] initWithEffect:blur];

    effectview.frame = CGRectMake(0, 0, _backView.frame.size.width
 
, CGRectGetHeight(_backView.frame));
    effectview.alpha = .6;
    [_backView addSubview:effectview];