将XAML窗口转换为位图

Question

I have a simple XAML like this:

<UserControl x:Class="blabla.MyView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" 
         Name="myUserControl">
 <Grid Name="myGrid" Background="White">
    <TextBlock Name="myTextBlock"/>
 </Grid>
</UserControl>

Now I'd like to create a new view in the background by using this xaml. After this, I'd like to change the controls (or maybe add some controls by myself), save it to a Bitmap and assign it to the Clipboard (just to see the output). I would have tried it like this:

MyView view = new MyView();
view.myTextBlock.Text = "TEST";

Rect bounds = VisualTreeHelper.GetDescendantBounds(view);
DrawingVisual dv = new DrawingVisual();
using (DrawingContext ctx = dv.RenderOpen())
{
    VisualBrush vb = new VisualBrush(view);
    ctx.DrawRectangle(vb, null, new Rect(new System.Windows.Point(), bounds.Size));
}
RenderTargetBitmap bmp = new RenderTargetBitmap((int)view.ActualWidth, (int)view.ActualHeight, 96, 96, PixelFormats.Pbgra32);

bmp.Render(dv);

PngBitmapEncoder pngImage = new PngBitmapEncoder();
pngImage.Frames.Add(BitmapFrame.Create(bmp));
System.Windows.Clipboard.SetImage(pngImage.Frames[0]);

Unfortunately, the Size of the view is not being changed. Trying to set a hard coded width/height by produces a black image/bitmap.

How can I create a simple Bitmap out of a XAML?

Answer 1

Making the comment to official answer. However, I see that this solution is not the most elegant one. General thing is, that the window, resp. view, will result in black area when rendered while it is not visible/redered itself by showing it anyhow.

The workarround would be to show this view (as you wrote, but in Window). Small idea doing this, move the window out of visible screen to avoid flickering. example:

        var v = new MainWindow();
        v.Top = -10000; // far away
        v.Left = -10000; // far away
        v.Show();
        // .. do rendering
        v.Close();