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
expandToLevel = level;
    }
    /**
     * The <code>AbstractTreeViewer</code> implementation of this method
     * checks to ensure that the content provider is an <code>ITreeContentProvider</code>.
     */
    public void setContentProvider(IContentProvider provider) {
    	
        super.setContentProvider(provider);
    }
    
	protected void assertContentProviderType(IContentProvider provider) {
		Assert.isTrue(provider instanceof ITreeContentProvider || provider instanceof ITreePathContentProvider);
	}
    /**
     * Sets the expand state of the given item.
     * 
     * @param item
     *           the item
     * @param expand
     *           the expand state of the item
     */
    protected abstract void setExpanded(Item item, boolean expand);
    /**
     * Sets which nodes are expanded in this viewer's tree. The given list
     * contains the elements that are to be expanded; all other nodes are to be
     * collapsed.
     * <p>
     * This method is typically used when restoring the interesting state of a
     * viewer captured by an earlier call to <code>getExpandedElements</code>.