我认为最简单的解决方案是覆盖UIToolbar，它在iOS 7中模糊了它后面的所有东西。这很狡猾，但实现起来非常简单，而且速度很快!

你可以对任何视图这么做，只是让它成为UIToolbar的子类而不是UIView。你甚至可以用UIViewController的view属性来做，例如…

1)创建一个新类，它是UIViewController的“子类”，并选中“With XIB for user interface”。

2)选择View，进入右边面板中的标识检查器(alt-command-3)。将“Class”改为UIToolbar。现在转到属性检查器(alt-command-4)，将“背景”颜色改为“清色”。

3)在主视图中添加子视图，并将其连接到接口中的IBOutlet。叫它backgroundColorView。它看起来像这样，是实现(.m)文件中的一个私有类别。

@interface BlurExampleViewController ()
@property (weak, nonatomic) IBOutlet UIView *backgroundColorView;
@end

4)转到视图控制器实现(.m)文件并更改-viewDidLoad方法，如下所示:

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.view.barStyle = UIBarStyleBlack; // this will give a black blur as in the original post
    self.backgroundColorView.opaque = NO;
    self.backgroundColorView.alpha = 0.5;
    self.backgroundColorView.backgroundColor = [UIColor colorWithWhite:0.3 alpha:1];
}

这将给你一个深灰色的视图，它模糊了它后面的一切。没有有趣的业务，没有缓慢的核心图像模糊，使用操作系统/SDK提供的一切。

你可以将这个视图控制器的视图添加到另一个视图，如下所示:

[self addChildViewController:self.blurViewController];
[self.view addSubview:self.blurViewController.view];
[self.blurViewController didMoveToParentViewController:self];

// animate the self.blurViewController into view

如果有什么不清楚的地方请告诉我，我很乐意帮忙!

Edit

UIToolbar在7.0.3中被改变，当使用彩色模糊时可能会产生不希望看到的效果。

我们过去能够使用barTintColor设置颜色，但如果你以前这样做，你将需要将alpha组件设置为小于1。否则你的UIToolbar将是完全不透明的颜色-没有模糊。

这可以通过如下方式实现:(记住self是UIToolbar的子类)

UIColor *color = [UIColor blueColor]; // for example
self.barTintColor = [color colorWithAlphaComponent:0.5];

这将给模糊的视图一个蓝色的色调。

以下是Swift 2.0解决方案的代码，已经在接受的答案中提供:

    //only apply the blur if the user hasn't disabled transparency effects
    if !UIAccessibilityIsReduceTransparencyEnabled() {
        self.view.backgroundColor = UIColor.clearColor()

        let blurEffect = UIBlurEffect(style: UIBlurEffectStyle.Dark)
        let blurEffectView = UIVisualEffectView(effect: blurEffect)
        //always fill the view
        blurEffectView.frame = self.view.bounds
        blurEffectView.autoresizingMask = [.FlexibleWidth, .FlexibleHeight]

        self.view.addSubview(blurEffectView) //if you have more UIViews, use an insertSubview API to place it where needed
    } else {
        self.view.backgroundColor = UIColor.blackColor()
    }

func blurBackgroundUsingImage(image: UIImage)
{
    var frame                   = CGRectMake(0, 0, self.view.frame.width, self.view.frame.height)
    var imageView               = UIImageView(frame: frame)
    imageView.image             = image
    imageView.contentMode       = .ScaleAspectFill
    var blurEffect              = UIBlurEffect(style: .Light)
    var blurEffectView          = UIVisualEffectView(effect: blurEffect)
    blurEffectView.frame        = frame
    var transparentWhiteView    = UIView(frame: frame)
    transparentWhiteView.backgroundColor = UIColor(white: 1.0, alpha: 0.30)
    var viewsArray              = [imageView, blurEffectView, transparentWhiteView]

    for index in 0..<viewsArray.count {
        if let oldView = self.view.viewWithTag(index + 1) {
            var oldView         = self.view.viewWithTag(index + 1)
            // Must explicitly unwrap oldView to access its removeFromSuperview() method as of Xcode 6 Beta 5
            oldView!.removeFromSuperview()
        }
        var viewToInsert        = viewsArray[index]
        self.view.insertSubview(viewToInsert, atIndex: index + 1)
        viewToInsert.tag        = index + 1
    }
}

简单的答案是添加一个子视图并改变它的alpha。

UIView *mainView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];
UIView *subView = [[UIView alloc] initWithFrame:popupView.frame];
UIColor * backImgColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"blue_Img.png"]];
subView.backgroundColor = backImgColor;
subView.alpha = 0.5;
[mainView addSubview:subView];

Swift 3版本的凯文的答案返回模糊的图像-

func blurBgImage(image: UIImage) -> UIImage? {
        let radius: CGFloat = 20;
        let context = CIContext(options: nil);
        let inputImage = CIImage(cgImage: image.cgImage!);
        let filter = CIFilter(name: "CIGaussianBlur");
        filter?.setValue(inputImage, forKey: kCIInputImageKey);
        filter?.setValue("\(radius)", forKey:kCIInputRadiusKey);

        if let result = filter?.value(forKey: kCIOutputImageKey) as? CIImage{

            let rect = CGRect(origin: CGPoint(x: radius * 2,y :radius * 2), size: CGSize(width: image.size.width - radius * 4, height: image.size.height - radius * 4))

            if let cgImage = context.createCGImage(result, from: rect){
                return UIImage(cgImage: cgImage);
                }
        }
        return nil;
    }

我决定发布一个书面的Objective-C版本，从接受的答案只是在这个问题上提供更多的选项。

- (UIView *)applyBlurToView:(UIView *)view withEffectStyle:(UIBlurEffectStyle)style andConstraints:(BOOL)addConstraints
{
  //only apply the blur if the user hasn't disabled transparency effects
  if(!UIAccessibilityIsReduceTransparencyEnabled())
  {
    UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:style];
    UIVisualEffectView *blurEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];
    blurEffectView.frame = view.bounds;

    [view addSubview:blurEffectView];

    if(addConstraints)
    {
      //add auto layout constraints so that the blur fills the screen upon rotating device
      [blurEffectView setTranslatesAutoresizingMaskIntoConstraints:NO];

      [view addConstraint:[NSLayoutConstraint constraintWithItem:blurEffectView
                                                       attribute:NSLayoutAttributeTop
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:view
                                                       attribute:NSLayoutAttributeTop
                                                      multiplier:1
                                                        constant:0]];

      [view addConstraint:[NSLayoutConstraint constraintWithItem:blurEffectView
                                                       attribute:NSLayoutAttributeBottom
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:view
                                                       attribute:NSLayoutAttributeBottom
                                                      multiplier:1
                                                        constant:0]];

      [view addConstraint:[NSLayoutConstraint constraintWithItem:blurEffectView
                                                       attribute:NSLayoutAttributeLeading
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:view
                                                       attribute:NSLayoutAttributeLeading
                                                      multiplier:1
                                                        constant:0]];

      [view addConstraint:[NSLayoutConstraint constraintWithItem:blurEffectView
                                                       attribute:NSLayoutAttributeTrailing
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:view
                                                       attribute:NSLayoutAttributeTrailing
                                                      multiplier:1
                                                        constant:0]];
    }
  }
  else
  {
    view.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.7];
  }

  return view;
}

如果你想要，如果你只支持纵向模式，或者我只是在这个函数中添加了一个标志来使用它们，可以删除这些限制。