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>
     * 
     * @param elements
     *           the array of expanded elements
     * @see #getExpandedElements
     */
    public void setExpandedElements(Object[] elements) {
        assertElementsNotNull(elements);
        CustomHashtable expandedElements = newHashtable(elements.length * 2 + 1);
        for (int i = 0; i < elements.length; ++i) {
            Object element = elements[i];
            
            
            
            
            internalExpand(element, false);
            expandedElements.put(element, element);
        }
        
        
        
        
        internalSetExpanded(expandedElements, getControl());
    }
    /**
     * Sets which nodes are expanded in this viewer's tree. The given list
     * contains the tree paths that are to be expanded; all other nodes are to
     * be collapsed.
     * <p>
     * This method is typically used when restoring the interesting state of a