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
}
    /**
     * Return whether the tree node representing the given element or path can be
     * expanded. Clients should query expandablity by path if the viewer's
     * content provider is an {@link ITreePathContentProvider}.
     * <p>
     * The default implementation of this framework method calls <code>hasChildren</code>
     * on this viewer's content provider. It may be overridden if necessary.
     * </p>
     * 
     * @param elementOrTreePath
     *           the element or path
     * @return <code>true</code> if the tree node representing the given
     *         element can be expanded, or <code>false</code> if not
     */
    public boolean isExpandable(Object elementOrTreePath) {
    	Object element;
    	TreePath path;
    	if (elementOrTreePath instanceof TreePath) {
			path = (TreePath) elementOrTreePath;
			element = path.getLastSegment();
		} else {
			element = elementOrTreePath;
			path = null;
		}
        IContentProvider cp = getContentProvider();
        if (cp instanceof ITreePathContentProvider) {
			ITreePathContentProvider tpcp = (ITreePathContentProvider) cp;
			if (path == null) {