如何在ios xamarin c#中获得正确的触摸像素值

Question

你好，我正在尝试在Xamarin C#中获取触摸像素的颜色，但我有时会得到错误的值，我得到R=255，G=0，B=0，A=0我的代码中有什么问题？

 private UIColor ColorOfPoint(CGPoint point)
    {
        byte[] pixel = {0,0,0,0};

        using(CGColorSpace oColorSpace = CGColorSpace.CreateDeviceRGB())
        using(CGBitmapContext oContext = new CGBitmapContext(pixel,
                                                     1, 1, 8, 4, oColorSpace, CGBitmapFlags.PremultipliedLast & CGBitmapFlags.AlphaInfoMask))
        {
            oContext.TranslateCTM(-point.X,-point.Y);
            img.Layer.RenderInContext(oContext);
            oContext.Dispose();
            oColorSpace.Dispose();
        }

        UIColor color = new UIColor(pixel[0]/255,pixel[1]/255,pixel[2]/255,pixel[3]/255);
        return color;
    }

Answer 1

使用UIColor.FromRGBA而不是new UIColor(....)

我是这样做的：

byte[] alphaPixel = { 0, 0, 0, 0 };
protected UIColor GetColorAtTouchPoint(CGPoint point)
{
    var colorSpace = CGColorSpace.CreateDeviceRGB();
    var bitmapContext = new CGBitmapContext(alphaPixel, 1, 1, 8, 4, colorSpace, CGBitmapFlags.PremultipliedLast);
    bitmapContext.TranslateCTM(-point.X, -point.Y);
    view.Layer.RenderInContext(bitmapContext);
    return UIColor.FromRGBA(alphaPixel[0], alphaPixel[1], alphaPixel[2], alphaPixel[3]);
}