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
if (parentElementOrTreePath instanceof TreePath) {
			TreePath path = (TreePath) parentElementOrTreePath;
			Widget w = internalFindItem(path);
			if (w == null) {
				widgets = new Widget[] { };
			} else {
				widgets = new Widget[] { w };
			}
		} else {
			widgets = findItems(parentElementOrTreePath);
		}
		return widgets;
	}
	/**
	 * Return the item at the given path or <code>null</code>
	 * @param path the path
	 * @return the item at that path
	 * TODO could probably do better than this
	 */
	private Widget internalFindItem(TreePath path) {
		Widget[] widgets = findItems(path.getLastSegment());
		for (int i = 0; i < widgets.length; i++) {
			Widget widget = widgets[i];
			if (widget instanceof Item) {
				Item item = (Item) widget;
				TreePath p = getTreePathFromItem(item);
				if (p.equals(path)) {
					return widget;
				}			
			}