swift 扩展用于更改UIImage。这对于UIButton的设置突出显示图像很有用。

Posted 2021-05-19

//
//  UIImage+Extension.swift
//
//  Created by Yukito Shibuya on 2016/10/08.
//  Copyright © 2016年 yukitoto. All rights reserved.
//

import UIKit

extension UIImage {
    
    func imageWithAlphaComponent(alpha: CGFloat) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(self.size, false, 0)
        
        let ctx = UIGraphicsGetCurrentContext()
        let area = CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height)
        
        CGContextScaleCTM(ctx, 1, -1)
        CGContextTranslateCTM(ctx, 0, -area.size.height)
        
        CGContextSetBlendMode(ctx, CGBlendMode.Multiply)
        
        CGContextSetAlpha(ctx, alpha)
        
        CGContextDrawImage(ctx, area, self.CGImage)
        
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        
        UIGraphicsEndImageContext()
        
        return newImage
    }
}