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
protected void createTreeItem(Widget parent, Object element, int index) {
        Item item = newItem(parent, SWT.NULL, index);
        updateItem(item, element);
        updatePlus(item, element);
    }
    /**
     * The <code>AbstractTreeViewer</code> implementation of this method also
     * recurses over children of the corresponding element.
     */
    protected void disassociate(Item item) {
        super.disassociate(item);
        
        
        
        if (usingElementMap()) {
			disassociateChildren(item);
		}
    }
    /**
     * Disassociates the children of the given SWT item from their
     * corresponding elements.
     * 
     * @param item
     *           the widget
     */
    private void disassociateChildren(Item item) {
        Item[] items = getChildren(item);
        for (int i = 0; i < items.length; i++) {
            if (items[i].getData() != null) {
				disassociate(items[i]);