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
protected abstract Item newItem(Widget parent, int style, int index);
    /**
     * Removes the given elements from this viewer. The selection is updated if
     * required.
     * <p>
     * This method should be called (by the content provider) when elements
     * have been removed from the model, in order to cause the viewer to
     * accurately reflect the model. This method only affects the viewer, not
     * the model.
     * </p>
     * 
     * @param elementsOrTreePaths
     *           the elements to remove
     */
    public void remove(final Object[] elementsOrTreePaths) {
        assertElementsNotNull(elementsOrTreePaths);
        if (elementsOrTreePaths.length == 0) {
        	return;
        }
        preservingSelection(new Runnable() {
            public void run() {
                internalRemove(elementsOrTreePaths);
            }
        });
    }
    
    /**
     * Removes the given elements from this viewer whenever they appear as children
     * of the given parent element. If the given elements also appear as children
     * of some other parent, the other parent will remain unchanged. The selection