下面是Swift中使用CIGaussianBlur的快速实现:

func blur(image 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);
    let result = filter?.valueForKey(kCIOutputImageKey) as! CIImage;
    let rect = CGRectMake(radius * 2, radius * 2, image.size.width - radius * 4, image.size.height - radius * 4)
    let cgImage = context.createCGImage(result, fromRect: rect);
    let returnImage = UIImage(CGImage: cgImage);

    return returnImage;
}

你可以使用UIVisualEffectView来实现这个效果。这是一个本地API，经过了性能和电池寿命的微调，而且很容易实现。

迅速:

//only apply the blur if the user hasn't disabled transparency effects
if !UIAccessibility.isReduceTransparencyEnabled {
    view.backgroundColor = .clear

    let blurEffect = UIBlurEffect(style: .dark)
    let blurEffectView = UIVisualEffectView(effect: blurEffect)
    //always fill the view
    blurEffectView.frame = self.view.bounds
    blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]

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

objective - c:

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

    UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleDark];
    UIVisualEffectView *blurEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];
    //always fill the view
    blurEffectView.frame = self.view.bounds;
    blurEffectView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;

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

如果你以模态方式呈现这个视图控制器来模糊底层内容，你需要将模态呈现风格设置为Over Current Context，并将背景颜色设置为clear，以确保底层视图控制器在顶部呈现时仍然可见。

这是偶然发现的，给了我真正伟大的(几乎复制与苹果)的结果，并使用加速框架。——http://pastebin.com/6cs6hsyQ 不是我写的

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。

2019代码

下面是一个使用@AdamBardon技巧的更完整的例子。

@IBDesignable class ButtonOrSomethingWithBlur: UIButton {

    var ba: UIViewPropertyAnimator?
    private lazy var blurry: BlurryBall = { return BlurryBall() }()

    override func didMoveToSuperview() {
        super.didMoveToSuperview()
        
        // Setup the blurry ball.  BE SURE TO TEARDOWN.
        // Use superb trick to access the internal guassian level of Apple's
        // standard gpu blurrer per stackoverflow.com/a/55378168/294884
        
        superview?.insertSubview(blurry, belowSubview: self)
        ba = UIViewPropertyAnimator(duration:1, curve:.linear) {[weak self] in
            // note, those duration/curve values are simply unusued
            self?.blurry.effect = UIBlurEffect(style: .extraLight)
        }
        ba?.fractionComplete = live.largeplaybutton_blurfactor
    }
    
    override func willMove(toSuperview newSuperview: UIView?) {
        
        // Teardown for the blurry ball - critical
        
        if newSuperview == nil { print("safe teardown")
            ba?.stopAnimation(true)
            ba?.finishAnimation(at: .current)
        }
    }

    override func layoutSubviews() { super.layoutSubviews()
        blurry.frame = bounds, your drawing frame or whatever
    }

{题外话:作为一个通用的iOS工程问题，didMoveToWindow可能比didMoveToSuperview更适合你。其次，您可以使用其他一些方法来执行拆卸操作，但是拆卸操作就是这里显示的两行代码。

bluryball只是一个UIVisualEffectView。注意视觉效果视图的初始值。如果你碰巧需要圆角或者其他东西，在这门课上做吧。

class BlurryBall: UIVisualEffectView {
    
    override init(effect: UIVisualEffect?) { super.init(effect: effect)
        commonInit() }
    
    required init?(coder aDecoder: NSCoder) { super.init(coder: aDecoder)
        commonInit() }
    
    private func commonInit() {
        clipsToBounds = true
        backgroundColor = .clear
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        layer.cornerRadius = bounds.width / 2
    }
}

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];