CODEWITHSUNDEEP
c#wpfxaml
Hardgraf
Hardgraf

Reputation: 2646

Simple DrawingContext not drawing to UI

I have a RenderChart method encaspsulated in the code behind of a UserControl which will hopefully draw some charts on a map. I have simplified the method to try to get some text rendered but without success:

 private void RenderChart()
    {
        DrawingVisual newVisual = new DrawingVisual();

        using (DrawingContext dc = newVisual.RenderOpen())
        {
           Rect rect = new Rect(new Point(160, 100), new System.Windows.Size(320, 80));

                dc.DrawRectangle(Brushes.Maroon, (Pen)null, rect);
                dc.Close();          
        }

        if (this.visual != null)
        {
            this.RemoveVisualChild(this.visual);
        }              

        this.AddVisualChild(newVisual);
        this.visual = newVisual;

        this.RefreshMargin();
    }

Whenever I've drawn simple shapes etc before I've used for example myCanvas.Children.Add(myEllipse);

Infact If I define an Ellipse & add it to a canvas as abovewithout using the DrawingContext I get the result I expect.

Do I need to add the drawing context to a panel in my control or is there some other reason as to why is won't render in the UI?

Upvotes: 0

Views: 900

Answers (1)

Steven Rands
Steven Rands

Reputation: 5421

The UserControl class ultimately derives from a class called UIElement, which defines a virtual OnRender method that you can override to "draw" on the control (as Clemens suggests in a question comment). The following example will draw a blue rectangle the same size as the user control:

protected override void OnRender(DrawingContext dc)
{
    dc.DrawRectangle(Brushes.Blue, null, new Rect(0, 0, ActualWidth, ActualHeight));
}

I would suggest that overriding OnRender is the more traditional way to approach this rather than attempting to use a DrawingVisual. The only potential issue you might have with this technique is that your drawing will appear behind all of the other controls contained in your user control.

Upvotes: 1

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