iOS8自带模糊效果

   typedef NS_ENUM(NSInteger, UIBlurEffectStyle) {  
    UIBlurEffectStyleExtraLight,  
    UIBlurEffectStyleLight,  
    UIBlurEffectStyleDark  
} NS_ENUM_AVAILABLE_IOS(8_0);  
  
  
    UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleDark];  
    UIVisualEffectView *blurEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];  
    blurEffectView.frame = self.imageView.bounds;  
    [self.imageView insertSubview:blurEffectView atIndex:0];