void OnWorkspaceRegionRegister(object sender, WorkspaceRegionEventArgs e)
 {
     e.Handled = true;
     if (!regions.ContainsKey(e.Region.Id))
     {
         regions.Add(e.Region.Id, e.Region);
     }
     if (!workspaceChanging)
     {
         SyncWorkspaceRegionLayout(e.Region);
     }
 }
 void OnWorkspaceRegionUnregister(object sender, WorkspaceRegionEventArgs e)
 {
     e.Handled = true;
     regions.Remove(e.Region.Id);
 }