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
* <p>
     * The default implementation of this framework method assumes that <code>widget.getData()</code>
     * returns the element corresponding to the node. Note: the node is not
     * visually expanded! You may have to call <code>parent.setExpanded(true)</code>.
     * </p>
     * 
     * @param widget
     *           the widget
     */
    protected void createChildren(final Widget widget) {
        final Item[] tis = getChildren(widget);
        if (tis != null && tis.length > 0) {
            Object data = tis[0].getData();
            if (data != null) {
				return; 
			}
        }
        BusyIndicator.showWhile(widget.getDisplay(), new Runnable() {
            public void run() {
                
                
                if (tis != null) {
                    for (int i = 0; i < tis.length; i++) {
                        if (tis[i].getData() != null) {
                            disassociate(tis[i]);
                            Assert.isTrue(tis[i].getData() == null,
                                    "Second or later child is non -null");
                        }
                        tis[i].dispose();
                    }