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
*/
	private int internalCompare(ViewerComparator comparator, TreePath parentPath, Object e1, Object e2) {
		if (comparator instanceof TreePathViewerSorter) {
			TreePathViewerSorter tpvs = (TreePathViewerSorter) comparator;
			return tpvs.compare(this, parentPath, e1, e2);
		}
		return comparator.compare(this, e1, e2);
	}
	
	/* (non-Javadoc)
	 * @see org.eclipse.jface.viewers.StructuredViewer#getSortedChildren(java.lang.Object)
	 */
	protected Object[] getSortedChildren(Object parentElementOrTreePath) {
		Object[] result =  getFilteredChildren(parentElementOrTreePath);
		ViewerComparator comparator = getComparator();
		if (parentElementOrTreePath!=null && comparator instanceof TreePathViewerSorter) {
			TreePathViewerSorter tpvs = (TreePathViewerSorter) comparator;
			
			
			result = (Object[]) result.clone();
			
			TreePath path = null;
	    	if (parentElementOrTreePath instanceof TreePath) {
	    		path = (TreePath) parentElementOrTreePath;
			} else {
				Object parent = parentElementOrTreePath;
				Widget w = internalGetWidgetToSelect(parent);
				if (w != null) {
					path = internalGetSorterParentPath(w, comparator);
				}