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
* @param widget
     *           the widget
     * @param level
     *           non-negative level, or <code>ALL_LEVELS</code> to collapse
     *           all levels of the tree
     */
    protected void internalExpandToLevel(Widget widget, int level) {
        if (level == ALL_LEVELS || level > 0) {
    		createChildren(widget);
            if (widget instanceof Item) {
				setExpanded((Item) widget, true);
			}
            if (level == ALL_LEVELS || level > 1) {
                Item[] children = getChildren(widget);
                if (children != null) {
                    int newLevel = (level == ALL_LEVELS ? ALL_LEVELS
                            : level - 1);
                    for (int i = 0; i < children.length; i++) {
						internalExpandToLevel(children[i], newLevel);
					}
                }
            }
        }
    }
    /**
     * Non-recursively tries to find the given element as a child of the given
     * parent (item or tree).
     * 
     * @param parent
     *           the parent item