如何在iOS Xamarin C＃中获得正确的触摸像素值

Question

Hello i am trying to get the color of pixel on touch in Xamarin C#, but i get wrong values at times,i get R=255,G=0,B=0,A=0 What's wrong in my code?

 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

Use UIColor.FromRGBA instead of new UIColor(....)

This is how I do:

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]);
}