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 element
     *           the element
     * @return Widget
     */
    private Widget internalFindChild(Widget parent, Object element) {
        Item[] items = getChildren(parent);
        for (int i = 0; i < items.length; i++) {
            Item item = items[i];
            Object data = item.getData();
            if (data != null && equals(data, element)) {
				return item;
			}
        }
        return null;
    }
    /**
     * Recursively tries to find the given element.
     * 
     * @param parent
     *           the parent item
     * @param element
     *           the element
     * @return Widget
     */
    private Widget internalFindItem(Item parent, Object element) {
        
        Object data = parent.getData();
        if (data != null) {
            if (equals(data, element)) {
				return parent;