Get the child element of a Custom Class in XAML

Question

I have a custom class ModelWorkspace which derives from the Border and I've used it in my XAML as below:

XAML

<workspaces:ModelWorkspace x:Name="ModelWorkspace" ClipToBounds="True">
    <Canvas x:Name="ModelWindow" Width="0" Height="0">
    </Canvas>                
</workspaces:ModelWorkspace>

Custom Class

public class ModelWorkspace : Border
{
}

Now I want to write a constructor in this custom class and somehow access the child element of this custom class which is Canvas: ModelWindow in this case and then add a new Canvas to this child element.

public class ModelWorkspace : Border
{
    public Canvas innerLayer { get; set; }

    public ModelWorkspace()
    {
        innerLayer = new Canvas();
        // Get the child element here and add the
        // innerLayer as its child.
    }
}

So the final result should look something like this:

<workspaces:ModelWorkspace x:Name="ModelWorkspace" ClipToBounds="True">
    <Canvas x:Name="ModelWindow" Width="0" Height="0">
        <Canvas> // this is the inner layer we added by code.
        </Canvas>
    </Canvas>                
</workspaces:ModelWorkspace>

Update :

<Window x:Class="CustomClass.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:customClass="clr-namespace:CustomClass"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <customClass:ModelWorkspace>
            <Canvas x:Name="ModelWindow" Width="0" Height="0">
            </Canvas>
        </customClass:ModelWorkspace>
    </Grid>
</Window>

using System.Windows;
using System.Windows.Controls;

namespace CustomClass
{
    public class ModelWorkspace : Border
    {
        public Canvas innerLayer { get; set; }

        public ModelWorkspace()
        {
            innerLayer = new Canvas();

            // Add "innerLayer" to the canvas defined as the child of this ModelWorkspace.
            var childCanvas = Child as Canvas;
            if (childCanvas != null)
            {
                childCanvas.Children.Add(innerLayer);
                MessageBox.Show("This worked!");
            }
        }
    }
}

Answer 1

Since you have inherited from Border , which further inherits from Decorator , you can access the child element of your control with the Decorator.Child property.

public ModelWorkspace()
{
    InitializeComponent();

    innerLayer = new Canvas();

    // Add "innerLayer" to the canvas defined as the child of this ModelWorkspace.
    var childCanvas = Child as Canvas;
    if (childCanvas != null)
    {
        childCanvas.Children.Add(innerLayer);
    }
    // else the child is not a canvas.
}