在代码中而不是 XAML 中呈现 UserControl

我想用RenderTargetBitmap将 UserControl 呈现为位图，而无需为其编写 XAML。当我这样做时，我得到一张空白图像，我是否错过了关键的一步？

ValTool.Controls.VideoFisheyeOverlayControl vfoc = new Controls.VideoFisheyeOverlayControl();
vfoc.Width = (int)this.VideoContainer.ActualWidth;
vfoc.Height = (int)this.VideoContainer.ActualHeight;
vfoc.FieldsOfView=this.FieldsOfView;
vfoc.CountLines = this.CountLines;

vfoc.UpdateLayout();
vfoc.InvalidateVisual();

RenderTargetBitmap visual = new RenderTargetBitmap((int)this.VideoContainer.ActualWidth, (int)this.VideoContainer.ActualHeight, 96, 96, PixelFormats.Pbgra32);
visual.Render(vfoc);
var finalImage = BitmapFrame.Create(visual);
// Encoding the RenderBitmapTarget as a PNG file.
PngBitmapEncoder png = new PngBitmapEncoder();
png.Frames.Add(BitmapFrame.Create(finalImage));
using (Stream stm = File.Create(@"new.png"))
{
    png.Save(stm);
}

您必须调用而不是 UpdateLayoutMeasure http://msdn.microsoft.com/en-us/library/system.windows.uielement.measure.aspx and Arrange http://msdn.microsoft.com/en-us/library/system.windows.uielement.arrange%28v=vs.110%29.aspx完成布局：

var width = VideoContainer.ActualWidth;
var height = VideoContainer.ActualHeight;

vfoc.Measure(new Size(width, height));
vfoc.Arrange(new Rect(0, 0, width, height));
vfoc.InvalidateVisual();