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 listener
     *           a tree viewer listener
     */
    public void addTreeListener(ITreeViewerListener listener) {
        treeListeners.add(listener);
    }
    /**
     * Adds the given SWT tree listener to the given SWT control.
     * 
     * @param control
     *           the SWT control
     * @param listener
     *           the SWT tree listener
     */
    protected abstract void addTreeListener(Control control,
            TreeListener listener);
    
    protected void associate(Object element, Item item) {
        Object data = item.getData();
        if (data != null && data != element && equals(data, element)) {
            
            
            
            unmapElement(data, item);
            item.setData(element);
            mapElement(element, item);
        } else {
            
            super.associate(element, item);