Bug 138608 [Viewers] JFace AbstractTreeViewer: itemExists doesn't handle equal tree entries
I use a TreeViewer with - setUseHashLookup(true) - without any sorter or filter - with a comparer When I try to add an object that is equal to an existing entry in the tree, it will not be added. This is because the method private boolean itemExists(Item[] items, Object element) { if(usingElementMap()) { return findItem(element) != null; } for (int i = 0; i < items.length; i++) { if(items[i].getData().equals(element)) { return true; } } return false; } takes a shortcut if there is an element map, but the shortcut doesn't handle the 'multiple equal elements' case. There is a workaround, however: Setting a dummy sorter will avoid the call to itemExists and multiple equal elements can be added to the tree.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* @param event
     *           the SWT tree event
     */
    protected void handleTreeCollapse(TreeEvent event) {
        if (event.item.getData() != null) {
            fireTreeCollapsed(new TreeExpansionEvent(this, event.item.getData()));
        }
    }
    /**
     * Handles a tree expand event from the SWT widget.
     * 
     * @param event
     *           the SWT tree event
     */
    protected void handleTreeExpand(TreeEvent event) {
    	if (!(getContentProvider() instanceof ILazyTreeContentProvider)) {
			createChildren(event.item);
		}
        if (event.item.getData() != null) {
            fireTreeExpanded(new TreeExpansionEvent(this, event.item.getData()));
        }
    }
    
    protected void hookControl(Control control) {
        super.hookControl(control);
        addTreeListener(control, new TreeListener() {
            public void treeExpanded(TreeEvent event) {
                handleTreeExpand(event);
            }
            public void treeCollapsed(TreeEvent event) {