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
Object newElement = elementChildren[i];
			setExpanded(item, expanded.containsKey(newElement)); 
		}
        
        
        if (min < elementChildren.length) {
            for (int i = min; i < elementChildren.length; ++i) {
                createTreeItem(widget, elementChildren[i], i);
            }
            
            
            
            if (expanded.size() > 0) {
                
                items = getChildren(widget);
                for (int i = min; i < elementChildren.length; ++i) {
                    
                    
                    
                    
                    
                    
                    if (expanded.containsKey(elementChildren[i])) {
                        setExpanded(items[i], true);
                    }
                }
            }
        }
        
        if (widget == tree && oldCnt == 0 && getItemCount(tree) != 0) {