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
tree.setRedraw(false);
            tree.setRedraw(true);
        }
    }
    /**
     * Updates the "+"/"-" icon of the tree node from the given element. It
     * calls <code>isExpandable</code> to determine whether an element is
     * expandable.
     * 
     * @param item
     *           the item
     * @param element
     *           the element
     */
    protected void updatePlus(Item item, Object element) {
        boolean hasPlus = getItemCount(item) > 0;
        boolean needsPlus = isExpandable(item, null, element);
        boolean removeAll = false;
        boolean addDummy = false;
        Object data = item.getData();
        if (data != null && equals(element, data)) {
            
            if (hasPlus != needsPlus) {
                if (needsPlus) {
					addDummy = true;
				} else {
					removeAll = true;
				}
            }