I tried the following code but i'm not able to have a navigation bar automatically resizing its parent when it is minimized (i.e. the splitcontainer).  Is there a solution to this problem ? Thanks.
        <docking:DockSite Name="DockSite">
          <docking:SplitContainer Orientation="Horizontal">
             <docking:ToolWindowContainer>
                  <docking:ToolWindow>
                            <navigation:NavigationBar x:Name="NB">
                               (...)
                            </navigation:NavigationBar>
                  </docking:ToolWindow>
              </docking:ToolWindowContainer>                           
              <docking:Workspace>
                (...)
              </docking:Workspace>     
          </docking:SplitContainer>
        </docking:DockSite>