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
protected Widget internalExpand(Object elementOrPath, boolean expand) {
        if (elementOrPath == null) {
			return null;
		}
        Widget w = internalGetWidgetToSelect(elementOrPath);
        if (w == null) {
            if (equals(elementOrPath, getRoot())) { 
                return null;
            }
            
            Object parent = getParentElement(elementOrPath);
            if (parent != null) {
                Widget pw = internalExpand(parent, false);
                if (pw != null) {
                    
                    createChildren(pw);
                    Object element = internalToElement(elementOrPath);
                    w = internalFindChild(pw, element);
                    if (expand && pw instanceof Item) {
                    	
                    	Item item = (Item) pw;
                    	LinkedList toExpandList = new LinkedList();
                    	while (item != null && !getExpanded(item)) {
                    		toExpandList.addFirst(item);
                    		item = getParentItem(item);
                    	}
                    	for(Iterator it = toExpandList.iterator(); it.hasNext();) {
                    		Item toExpand = (Item) it.next();
                    		setExpanded(toExpand, true);
                    	}