WPF: How to autosize Path to its container?

I changed the Stackpanel to Grid and Stretch property of the Path to Fill.

<Grid x:Name="TrackSurface"> <Path Fill="AliceBlue" Stretch="Fill"      Stroke="Black" StrokeThickness="1"       Data="M148,28 C221,133 110.50025,119.5 110.50025,119.5 L124.50016,68.5 z"> </Path> 

Any reason why you're not using a ViewBox for this? That will shrink or grow the path as needed. If you don't want it scaled, but rather clipped, then set the clipping mode to be restricted to the control's bounding box. (I'd wrap the path in a ContentPresenter for that.)

Ensure that your path is smaller than your StackPanel.

Easiest way for a very easy path will be to move the comma in every number (i.e. divide everything by 10 or 100 in TranslateZ), or for more complicated paths add a LayoutTransform (lower the scaling factor as needed):

<StackPanel x:Name="TrackSurface">    <Path Fill="AliceBlue" Stroke="Black" StrokeThickness="1"           Data="{StaticResource TranslateZ}">          <Path.LayoutTransform>               <ScaleTransform ScaleX="0.1" ScaleY="0.1"/>          </Path.LayoutTransform>    </Path></StackPanel>

Some Remarks:

I had a similar problem, with a button template containing a path. The button's "auto" size was determined by the path, because the path had the largest dimensions of the template content.

This in itself might not turn out as a problem, because if you specify the button's height/width, or if the button's Horizontal-/VerticalAlignment is set to stretch, of course the path will scale.

For other values of Horizontal-/VerticalAlignment however, the button size gets determined by the amount of space required by its content, which in my case resulted in a button with the path's original dimensions.