WPF - ContentControl Content as DrawingVisual - wpf

Question

Can I set the Content property of a ContentControl to a DrawingVisual object? It says in the documentation that the content can be anything but I tried and nothing shows up when I add the control to canvas. Is it possible and if it is can you post the full code that adds a ContentControl, whose content is a DrawingVisual, to a canvas?

Answer 1

Can I set the Content property of a ContentControl to a DrawingVisual object?
Technically, yes, you can. However, that is probably not what you want. A DrawingVisual added to a ContentControl will simply display the string "System.Windows.Media.DrawingVisual". The following code within a grid will demonstrate this easilly:
<Button>
<DrawingVisual/>
</Button>
To use a DrawingVisual properly, you need to encapsulate it within a FrameworkElement. See the Microsoft Reference.
Thus, the following code should help do what you want.
<Window x:Class="TestDump.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TestDump"
Title="Window1" Height="300" Width="600" >
<Grid>
<Canvas>
<Button >
<local:MyVisualHost Width="600" Height="300"/>
</Button>
</Canvas>
</Grid>
</Window>
And on the C# side:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace TestDump
{
/// <summary>
/// Interaction logic for Window1.xaml
/// </summary>
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
}
}
public class MyVisualHost : FrameworkElement
{
private VisualCollection _children;
public MyVisualHost()
{
_children = new VisualCollection(this);
_children.Add(CreateDrawingVisualRectangle());
}
// Create a DrawingVisual that contains a rectangle.
private DrawingVisual CreateDrawingVisualRectangle()
{
DrawingVisual drawingVisual = new DrawingVisual();
// Retrieve the DrawingContext in order to create new drawing content.
DrawingContext drawingContext = drawingVisual.RenderOpen();
// Create a rectangle and draw it in the DrawingContext.
Rect rect = new Rect(new System.Windows.Point(160, 100), new System.Windows.Size(320, 80));
drawingContext.DrawRectangle(System.Windows.Media.Brushes.Blue, (System.Windows.Media.Pen)null, rect);
// Persist the drawing content.
drawingContext.Close();
return drawingVisual;
}
// Provide a required override for the VisualChildrenCount property.
protected override int VisualChildrenCount
{
get { return _children.Count; }
}
// Provide a required override for the GetVisualChild method.
protected override Visual GetVisualChild(int index)
{
if (index < 0 || index >= _children.Count)
{
throw new ArgumentOutOfRangeException();
}
return _children[index];
}
}
}