Disable parts SWT-Table/Tree with SWT.CHECK

This is a hack, a hack, a hack posting.

I have read many many entries on the newsgroups asking a question like this:

How can I disable certain check boxes in an SWT-Tree/Table. Is this possible?

The standard answer to this was: "Sorry no this is not possible". Today I faced the same problem (mine had to do with ViewerObservables#observeCheckElements()) where the user is not allowed to check the Top-Level-Nodes.

The tree looks like this:

+ Application 1
  + Privilege A
    + Privileg A1
  + Privilege B
    + Privileg B2
+ Application 1
  + Privileg C

The values bound are the ones in Privileg* so I have to lock the Application-checkboxes

The setup is something like this:

Databinding ctx = ....
IObservableSet mObs = ....

Tree tree = new Tree(parent,SWT.BORDER|SWT.V_SCROLL|SWT.H_SCROLL);
CheckBoxTreeViewer v = new CheckBoxTreeViewer(tree);
IObservableSet uiOs = ViewerObservables.observeCheckedElements(v,IPrivileges.class);
ctx.bindSet(uiObs,mObs,null,null);

I nearly gave up but then I had the following idea.

final Tree tree = new Tree(parent,SWT.BORDER|SWT.V_SCROLL|SWT.H_SCROLL);
// Attach a listener directly after the creation
tree.addListener(SWT.Selection,new Listener() {
   public void handleEvent(Event event) {
       if( event.detail == SWT.CHECK ) {
           if( !(event.item.getData() instanceof IPrivileg) ) {
              event.detail = SWT.NONE;
              event.type   = SWT.None;
              event.doIt   = false;
              try {
                 tree.setRedraw(false);
                 TreeItem item = (TreeItem)event.item;
                 item.setChecked(! item.getChecked() );
              } finally {
                 tree.setRedraw(true);
              }
           }
       }
   }
});

CheckBoxTreeViewer v = new CheckBoxTreeViewer(tree);
// ....

This is a hack, I only tested it on Win32 (XP) and don't know how cross platform it is so don't kill me for posting this hack of hacks.