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
} else {
            
            removeAll = true;
            addDummy = needsPlus;
            
            setExpanded(item, false);
        }
        if (removeAll) {
            
            Item[] items = getItems(item);
            for (int i = 0; i < items.length; i++) {
                if (items[i].getData() != null) {
					disassociate(items[i]);
				}
                items[i].dispose();
            }
        }
        if (addDummy) {
			newItem(item, SWT.NULL, -1); 
		}
    }
    /**
     * Gets the expanded elements that are visible to the user. An expanded
     * element is only visible if the parent is expanded.
     * 
     * @return the visible expanded elements
     * @since 2.0
     */
    public Object[] getVisibleExpandedElements() {
        ArrayList v = new ArrayList();