调整图像大小 - 没有宽高比

// resize the image (without trying to maintain aspect ratio)
public static UIImage ResizeImage(this UIImage sourceImage, float width, float height)
{
    UIGraphics.BeginImageContext(new SizeF(width, height));
    sourceImage.Draw(new RectangleF(0, 0, width, height));
    var resultImage = UIGraphics.GetImageFromCurrentImageContext();
    UIGraphics.EndImageContext();
    return resultImage;
}