Trees can have "unsynchronized" TreeStores ->NullPointers

[acerberus]

Hi,

there is a bug in Tree(Panel)s caused by unsynchronized Stores. If a Tree is given a TreeStore it adds handlers to listen to store events. For example an added entry in the store causes the tree to register a new node. Certain events, however, can cause the store and tree to become unsynchronized. Examples are:

• Filtering
• Loading store data before giving the store to the tree
• Probably more

If now an update on the store occurs, the tree's onUpdate method is called:

  protected void onUpdate(StoreUpdateEvent<M> event) {
    for (M item : event.getItems()) {
      TreeNode<M> node = findNode(item);
      if (node.model != item) {
        node.model = item;
      }
      refresh(item);
    }
  }

Here the tree assumes that a node corresponding to the updated StoreModel exists. However, due to the two not being completely synched, this may not be the case. In this case findNode(item) return null and the whole thing produces a NullPointerException:

Caused by: java.lang.NullPointerException
	at com.sencha.gxt.widget.core.client.tree.Tree$TreeNode.access$1(Tree.java:345)
	at com.sencha.gxt.widget.core.client.tree.Tree.onUpdate(Tree.java:1864)
	at com.sencha.gxt.widget.core.client.tree.Tree$Handler.onUpdate(Tree.java:510)
	at com.sencha.gxt.data.shared.event.StoreUpdateEvent.dispatch(StoreUpdateEvent.java:101)
	at com.sencha.gxt.data.shared.event.StoreUpdateEvent.dispatch(StoreUpdateEvent.java:1)
	at com.google.gwt.event.shared.GwtEvent.dispatch(GwtEvent.java:1)
	at com.google.web.bindery.event.shared.EventBus.dispatchEvent(EventBus.java:40)
	at com.google.web.bindery.event.shared.SimpleEventBus.doFire(SimpleEventBus.java:193)
	at com.google.web.bindery.event.shared.SimpleEventBus.fireEvent(SimpleEventBus.java:88)
	at com.google.gwt.event.shared.HandlerManager.fireEvent(HandlerManager.java:127)
	... 40 more

A temporary bugfix is to override the onUpdate method with the following:

	protected void onUpdate(StoreUpdateEvent<M> event) {
		for (M item : event.getItems()) {
			TreeNode<M> node = findNode(item);
			if(null == node)
				register(item);
		}
		super.onUpdate(event);
	}

This causes the missing nodes first to be registered and then "updated".