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 element
     * @return <code>true</code> if the element matches.
     */
	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;
	}
	/**
     * Returns the index where the item should be inserted. It uses sorter to
     * determine the correct position, if sorter is not assigned, returns the
     * index of the element after the last.
     * 
     * @param items the items to search
     * @param sorter The sorter to use.
     * @param lastInsertion
     *            the start index to start search for position from this allows
     *            optimising search for multiple elements that are sorted
     *            themself.
     * @param element
     *            element to find position for.
     * @param parentPath the tree path for the element's parent or <code>null</code>
     * if the element is a root element or the sorter is not a {@link TreePathViewerSorter}
     * @return the index to use when inserting the element.