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 void setSelection(List items);
    /**
     *  This implementation of setSelectionToWidget accepts a list of elements
     *  or a list of tree paths.
     **/
    protected void setSelectionToWidget(List v, boolean reveal) {
        if (v == null) {
            setSelection(new ArrayList(0));
            return;
        }
        int size = v.size();
        List newSelection = new ArrayList(size);
        for (int i = 0; i < size; ++i) {
            Object elementOrTreePath = v.get(i);
			
            
        	Widget w = internalExpand(elementOrTreePath, false);
            if (w instanceof Item) {
                newSelection.add(w);
            } else if (w == null && elementOrTreePath instanceof TreePath) {
            	TreePath treePath = (TreePath) elementOrTreePath;
				Object element = treePath.getLastSegment();
				if (element != null) {
					w = internalExpand(element, false);
					if (w instanceof Item) {
						newSelection.add(w);
					}
				}
            }