ios - 画一个简单的圆uiimage

Question

我尝试制作一个带有简单蓝色圆圈的 20x20 UIImage。我尝试使用此功能，但结果是黑色方 block 中的蓝色圆圈。如何去除圆圈周围的黑色方 block ？

功能:

+ (UIImage *)blueCircle {
    static UIImage *blueCircle = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(20.f, 20.f), YES, 0.0f);
        CGContextRef ctx = UIGraphicsGetCurrentContext();
        CGContextSaveGState(ctx);

        CGRect rect = CGRectMake(0, 0, 20, 20);
        CGContextSetFillColorWithColor(ctx, [UIColor cyanColor].CGColor);
        CGContextFillEllipseInRect(ctx, rect);

        CGContextRestoreGState(ctx);
        blueCircle = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

    });
    return blueCircle;
}

实际结果:

Answer 1

感谢您的问答! Swift代码如下:

extension UIImage {
    class func circle(diameter: CGFloat, color: UIColor) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(diameter, diameter), false, 0)
        let ctx = UIGraphicsGetCurrentContext()
        CGContextSaveGState(ctx)

        let rect = CGRectMake(0, 0, diameter, diameter)
        CGContextSetFillColorWithColor(ctx, color.CGColor)
        CGContextFillEllipseInRect(ctx, rect)

        CGContextRestoreGState(ctx)
        let img = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return img
    }
}

Schemetrical 提供的 Swift 3 版本:

extension UIImage {
    class func circle(diameter: CGFloat, color: UIColor) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(CGSize(width: diameter, height: diameter), false, 0)
        let ctx = UIGraphicsGetCurrentContext()!
        ctx.saveGState()

        let rect = CGRect(x: 0, y: 0, width: diameter, height: diameter)
        ctx.setFillColor(color.cgColor)
        ctx.fillEllipse(in: rect)

        ctx.restoreGState()
        let img = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()

        return img
    }
}