这个答案是基于Mitja Semolic之前出色的回答。我已经将它转换为swift 3，添加了一个解释，在评论中发生了什么，使它成为一个UIViewController的扩展，这样任何VC都可以随意调用它，添加了一个未模糊的视图来显示选择性应用，并添加了一个完成块，以便调用视图控制器可以在完成模糊时做任何它想做的事情。

    import UIKit
//This extension implements a blur to the entire screen, puts up a HUD and then waits and dismisses the view.
    extension UIViewController {
        func blurAndShowHUD(duration: Double, message: String, completion: @escaping () -> Void) { //with completion block
            //1. Create the blur effect & the view it will occupy
            let blurEffect = UIBlurEffect(style: UIBlurEffectStyle.light)
            let blurEffectView = UIVisualEffectView()//(effect: blurEffect)
            blurEffectView.frame = self.view.bounds
            blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]

        //2. Add the effect view to the main view
            self.view.addSubview(blurEffectView)
        //3. Create the hud and add it to the main view
        let hud = HudView.getHUD(view: self.view, withMessage: message)
        self.view.addSubview(hud)
        //4. Begin applying the blur effect to the effect view
        UIView.animate(withDuration: 0.01, animations: {
            blurEffectView.effect = blurEffect
        })
        //5. Halt the blur effects application to achieve the desired blur radius
        self.view.pauseAnimationsInThisView(delay: 0.004)
        //6. Remove the view (& the HUD) after the completion of the duration
        DispatchQueue.main.asyncAfter(deadline: .now() + duration) {
            blurEffectView.removeFromSuperview()
            hud.removeFromSuperview()
            self.view.resumeAnimationsInThisView()
            completion()
        }
    }
}

extension UIView {
    public func pauseAnimationsInThisView(delay: Double) {
        let time = delay + CFAbsoluteTimeGetCurrent()
        let timer = CFRunLoopTimerCreateWithHandler(kCFAllocatorDefault, time, 0, 0, 0, { timer in
            let layer = self.layer
            let pausedTime = layer.convertTime(CACurrentMediaTime(), from: nil)
            layer.speed = 0.0
            layer.timeOffset = pausedTime
        })
        CFRunLoopAddTimer(CFRunLoopGetCurrent(), timer, CFRunLoopMode.commonModes)
    }
    public func resumeAnimationsInThisView() {
        let pausedTime  = layer.timeOffset

        layer.speed = 1.0
        layer.timeOffset = 0.0
        layer.beginTime = layer.convertTime(CACurrentMediaTime(), from: nil) - pausedTime
    }
}

我已经确认它适用于iOS 10.3.1和iOS 11

你可以直接使用“带模糊的视觉效果视图”和“带模糊和活力的视觉效果视图”来创建背景模糊。

所有你需要做的是在iOS应用程序模糊背景…

在对象库中搜索“视觉效果模糊视图”

1 .图像

在你的故事板中拖动“带模糊的视觉效果视图”并设置它…

2 .图像

最后……你使你的应用程序背景模糊!

应用程序布局之前点击任何按钮!

应用程序视图后点击按钮，使整个应用程序背景模糊!

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。

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
    }
}

公认的答案是正确的，但这里缺少一个重要的步骤，如果这个视图-您想要模糊的背景-是使用

[self presentViewController:vc animated:YES completion:nil]

默认情况下，这将抵消模糊，因为UIKit删除演示者的视图，这实际上是模糊的。为了避免这种删除，将这一行添加到前一行之前

vc。modalPresentationStyle = UIModalPresentationOverFullScreen;

或者使用其他Over样式。

为了帮助大家，下面是我根据Jordan h的回答创建的一个快速扩展。它是用swift 5编写的，可以在Objective C中使用。

extension UIView {

    @objc func blurBackground(style: UIBlurEffect.Style, fallbackColor: UIColor) {
        if !UIAccessibility.isReduceTransparencyEnabled {
            self.backgroundColor = .clear

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

            self.insertSubview(blurEffectView, at: 0)
        } else {
            self.backgroundColor = fallbackColor
        }
    }

}

注意:如果你想在不影响文本的情况下模糊UILabel的背景，你应该创建一个容器UIView，将UILabel作为子视图添加到容器UIView，将UILabel的backgroundColor设置为UIColor。clear，然后调用blurBackground(style: UIBlurEffect。样式，fallbackColor: UIColor)的容器UIView。下面是用Swift 5写的一个简单的例子:

let frame = CGRect(x: 50, y: 200, width: 200, height: 50)
let containerView = UIView(frame: frame)
let label = UILabel(frame: frame)
label.text = "Some Text"
label.backgroundColor = UIColor.clear
containerView.addSubview(label)
containerView.blurBackground(style: .dark, fallbackColor: UIColor.black)