ios 画一个简单的圆 uiimage

Draw a simple circle uiimage

提问by Mattia Lancieri

I try to make a 20x20 UIImage with a simple blue circle. I try with this function, but the result is a blue circle in a black square. How do I remove the black square around the circle?

我尝试用一​​个简单的蓝色圆圈制作一个 20x20 的 UIImage。我尝试使用此功能，但结果是黑色方块中的蓝色圆圈。如何去除圆圈周围的黑色方块？

Function:

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;
}

actual result:

实际结果：

采纳答案by yurish

You need to include alpha channel into your bitmap: UIGraphicsBeginImageContextWithOptions(..., NO, ...)if you want to see what is behind the corners.

您需要在位图中包含 alpha 通道：UIGraphicsBeginImageContextWithOptions(..., NO, ...)如果您想查看角落后面的内容。

回答by superarts.org

Thanks for the Q&A! Swift code as below:

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
    }
}

Swift 3 version provided by Schemetrical:

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
    }
}

回答by Schemetrical

Swift 3 & 4:

斯威夫特 3 和 4：

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
    }
}

Swift autocorrect is godly. Thanks to Valentin.

Swift 自动更正是神圣的。感谢瓦伦丁。

回答by Jelle

Xamarin.iOS sample:

Xamarin.iOS 示例：

    public static UIImage CircleImage(nfloat diameter, UIColor color, bool opaque = false)
    {
        var rect = new CGRect(0, 0, diameter, diameter);

        UIGraphics.BeginImageContextWithOptions(rect.Size, opaque, 0);
        var ctx = UIGraphics.GetCurrentContext();
        ctx.SaveState();

        ctx.SetFillColor(color.CGColor);
        ctx.FillEllipseInRect(rect);

        ctx.RestoreState();
        var img = UIGraphics.GetImageFromCurrentImageContext();
        UIGraphics.EndImageContext();

        return img;
    }

回答by Amr Angry

Try this

尝试这个

UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, NO, 1.0);

回答by CodeBender

A custom initializer for creating a circle with a specific diameter and color:

用于创建具有特定直径和颜色的圆的自定义初始值设定项：

extension UIImage {
    convenience init?(diameter: CGFloat, color: UIColor) {
        let size = CGSize(width: diameter, height: diameter)
        UIGraphicsBeginImageContextWithOptions(size, false, 0)
        guard let contex = UIGraphicsGetCurrentContext() else {
            return nil
        }

        contex.saveGState()
        let rect = CGRect(origin: .zero, size: size)
        contex.setFillColor(color.cgColor)
        contex.fillEllipse(in: rect)
        contex.restoreGState()

        guard let image = UIGraphicsGetImageFromCurrentImageContext(),
        let cgImage = image.cgImage else {
            return nil
        }
        UIGraphicsEndImageContext()

        self.init(cgImage: cgImage)
    }
}