推荐第三方库：
https://github.com/nicklockwood/FXBlurView
FXBlurView*Fx=[[FXBlurView alloc]initWithFrame:CGRectMake(, , , )];
Fx.dynamic=YES;
Fx.blurRadius=20.0;
Fx.tintColor=[UIColor blackColor];
[self.view addSubview:Fx];
ios8后有相应的系统类和方法很简单如下
UIBlurEffect*effect=[UIBlurEffect effectWithStyle:UIBlurEffectStyleDark];
UIVisualEffectView*effectView=[[UIVisualEffectView alloc]initWithEffect:effect];
effectView.frame=CGRectMake(, , , );
[self.view addSubview:effectView];
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