Swift - UIView的无损截图

效果

源码

//
//  UIView+ScreensShot.swift
//  Swift-Animations
//
//  Created by YouXianMing on 16/9/5.
//  Copyright © 2016年 YouXianMing. All rights reserved.
//

import UIKit

extension UIView {

    /**
     Get the view's screen shot, this function may be called from any thread of your app.

     - returns: The screen shot's image.
     */
    func screenShot() -> UIImage? {

        guard frame.size.height >  && frame.size.width >  else {

            return nil
        }

        UIGraphicsBeginImageContextWithOptions(frame.size, false, )
        layer.renderInContext(UIGraphicsGetCurrentContext()!)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return image
    }
}

使用

//
//  ViewController.swift
//  ScreenShot
//
//  Created by YouXianMing on 16/9/5.
//  Copyright © 2016年 YouXianMing. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {

        super.viewDidLoad()

        let redView             = UIView(frame: CGRectMake(, , , ))
        redView.backgroundColor = UIColor.redColor().colorWithAlphaComponent(0.5)
        view.addSubview(redView)

        let imageView = UIImageView(image: redView.screenShot())
        view.addSubview(imageView)
    }
}