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 Object getParentElement(Object elementOrTreePath) {
    	if(elementOrTreePath instanceof TreePath) {
    		TreePath treePath = (TreePath)elementOrTreePath;
    		if(treePath.getSegmentCount() <= 1) {
    			return null;
    		}
			return (treePath).getParentPath();
    	}
        IContentProvider cp = getContentProvider();
        if (cp instanceof ITreePathContentProvider) {
			ITreePathContentProvider tpcp = (ITreePathContentProvider) cp;
			TreePath[] paths = tpcp.getParents(elementOrTreePath);
			if (paths.length > 0) {
				if (paths[0].getSegmentCount() == 0) {
					return getInput();
				}
				return paths[0].getLastSegment();
			}
		}
        if (cp instanceof ITreeContentProvider) {
        	ITreeContentProvider tcp = (ITreeContentProvider) cp;
        	return tcp.getParent(elementOrTreePath);
        }
        return null;
	}
	/**
     * Returns the widget to be selected for the given element or tree path.
     * 
     * @param elementOrTreePath the element or tree path to select
     * @return the widget to be selected, or <code>null</code> if not found