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 result
     *           a list (element type: <code>Item</code>) into which to
     *           collect the elements
     * @param widget
     *           the widget
     */
    private void internalCollectExpandedItems(List result, Widget widget) {
        Item[] items = getChildren(widget);
        for (int i = 0; i < items.length; i++) {
            Item item = items[i];
            if (getExpanded(item)) {
            	result.add(item);
            }
            internalCollectExpandedItems(result, item);
        }
    }
    /**
     * Tries to create a path of tree items for the given element or tree path.
     * This method recursively walks up towards the root of the tree and in the
     * case of an element (rather than a tree path) assumes that
     * <code>getParent</code> returns the correct parent of an element.
     * 
     * @param elementOrPath
     *           the element
     * @param expand
     *           <code>true</code> if all nodes on the path should be
     *           expanded, and <code>false</code> otherwise
     * @return Widget
     */