How to use dockpanel to stretch a canvas?

<DockPanel Name="dcPa开发者_如何转开发nel">
    <Button Name="TopRect" DockPanel.Dock="Top" Background="LightGreen"
        Height="50" Content="Top" Margin="30,50,0,0" />
</DockPanel>

The code above stretch a button if I maximize the window. How can I add a Canvas inside the dockpanel, so when I maximize the window, all the canvas content will be stretched? thanks!

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The DockPanel will stretch the Canvas, but the Canvas will never stretch it's children. The Canvas always uses the desired size of it's children when arranging them.

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Try setting the Width, and Height to Auto. (of a canvas you can add)

EDIT:
I used this code, and it works perfectly:

<DockPanel>
    <Canvas Background="Black" />
</DockPanel>