set or unset column image on column click

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@35340 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/listctrl/listtest.cpp

@@ -722,7 +722,11 @@ void MyListCtrl::SetColumnImage(int col, int image)
 void MyListCtrl::OnColClick(wxListEvent& event)
 {
     int col = event.GetColumn();
-    SetColumnImage(col, 0);
+
+    // set or unset image
+    static x = false;
+    x = !x;
+    SetColumnImage(col, x ? 0 : -1);
 
     wxLogMessage( wxT("OnColumnClick at %d."), col );
 }