ios - 来自具有 alpha 的 UIColor 的 UIImage

Question

我正在尝试从我拥有的这个 UIColor 值创建一个 UIImage。正在创建 UIImage，但 alpha 值丢失。图像保持不透明。我正在使用以下代码:

@implementation GetImage

+ (UIImage *)imageWithColor:(UIColor *)color andSize:(CGSize)size
{
    UIImage *img = nil;

    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context,
                               color.CGColor);
    CGContextFillRect(context, rect);

    img = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return img;
}

@end

我这样调用它:

-(void) setButtonColours{

    UIImage *img1, *img2;

    UIColor *red = [UIColor colorWithRed:205.0/255.0 green:68.0/255.0 blue:51.0/255.0 alpha:1.0],
    *blue = [UIColor colorWithRed:71.0/255.0 green:97.0/255.0 blue:151.0/255.0 alpha:1.0];

    img1 = [GetImage imageWithColor: blue andSize: self.dummyButton.frame.size];

    img2 = [GetImage imageWithColor: red andSize: self.dummyButton.frame.size];

    [self.dummyButton setBackgroundImage: img1 forState:UIControlStateNormal];
    [self.dummyButton setBackgroundImage: img2 forState:UIControlStateSelected];

}

知道我错过了什么吗？

Answer 1

您正在创建不透明的图像上下文。

替换这一行:

UIGraphicsBeginImageContext(rect.size);

与:

UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0);