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 {
    			path = getTreePathFromItem(item);
    		}
    		ITreePathContentProvider cp = (ITreePathContentProvider) getContentProvider();
    		return cp != null && cp.hasChildren(path);
    	}
    	return isExpandable(element);
    }
    
    
    protected void labelProviderChanged() {
        
        Control tree = getControl();
        tree.setRedraw(false);
        
        internalRefresh(tree, getRoot(), false, true);
        tree.setRedraw(true);
    }
    /**
     * Creates a new item.
     * 
     * @param parent
     *           the parent widget
     * @param style
     *           SWT style bits
     * @param index
     *           if non-negative, indicates the position to insert the item
     *           into its parent
     * @return the newly-created item
     */