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
*/
     void internalRefreshStruct(Widget widget, Object element,
            boolean updateLabels) {
        updateChildren(widget, element, null, updateLabels);
        Item[] children = getChildren(widget);
        if (children != null) {
            for (int i = 0; i < children.length; i++) {
                Widget item = children[i];
                Object data = item.getData();
                if (data != null) {
					internalRefreshStruct(item, data, updateLabels);
				}
            }
        }
    }
    /**
     * Removes the given elements from this viewer.
     * <p>
     * EXPERIMENTAL.  Not to be used except by JDT.
     * This method was added to support JDT's explorations
     * into grouping by working sets, which requires viewers to support multiple 
     * equal elements.  See bug 76482 for more details.  This support will
     * likely be removed in Eclipse 3.2 in favour of proper support for
     * multiple equal elements. 
     * </p>
     * 
     * @param elementsOrPaths
     *           the elements or element paths to remove
     * @since 3.1
     */