无背景图的 UIButton 维持按下效果

众所周知，UIButton 只有在有背景图的时候，才有默认的按下效果
如果一个按钮只有背景色没有图片，按下是没有效果的。

解决思路就是能不能用颜色来生成一个图片呢。

下面直接上代码。

OC 代码

// 调用
[self.confirmButton setBackgroundImage:[self imageWithColor:[UIColor redColor]] forState:UIControlStateNormal];

- (UIImage *)imageWithColor:(UIColor *)color {
   CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);
   UIGraphicsBeginImageContext(rect.size);
   CGContextRef context = UIGraphicsGetCurrentContext();

   CGContextSetFillColorWithColor(context, [color CGColor]);
   CGContextFillRect(context, rect);

   UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();

   return image;
}

Swift 代码

class BaseButton: UIButton {
    override init(frame: CGRect) {
        super.init(frame: frame)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override var backgroundColor: UIColor? {
        didSet {
            let backgroundColor = self.backgroundColor ?? UIColor.white
            setBackgroundImage(generateMaskImage(from: backgroundColor), for: .normal)
        }
    }

    private func generateMaskImage(from color: UIColor) -> UIImage? {
        let rect = CGRect(x: 0, y: 0, width: 1, height: 1)
        UIGraphicsBeginImageContext(rect.size)
        let context = UIGraphicsGetCurrentContext()

        context?.setFillColor(color.cgColor)
        context?.fill(rect)

        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return image
    }
}