I need to show Nodes for objects that are slow to create. How do I compute Node children on a background thread?

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If you have a Node that needs to provide child Nodes, and computing the objects the child nodes represent is slow or expensive (i.e. you need to parse a file, connect to a database, or do some sort of I/O), you do not want to compute the child nodes in the event thread (which is what happens by default).

NetBeans 6.0 introduces org.openide.nodes.ChildFactory and Children.create(ChildFactory factory, boolean asynchronous). Simply subclass ChildFactory and implement protected boolean createKeys(List <T> toPopulate) to build the list of objects that will be represented by the child nodes. Implement protected Node createNodeForKey(T key) to create a Node - it will be passed each object in the list of child objects. createKeys will be called on a background thread.

Typically you’ll want to make the model object from createKeys available on the Node you create. So a simple implementation of createNodeForKey would look something like:

    protected Node createNodeForKey(T key) {
        AbstractNode result = new AbstractNode (Children.LEAF, Lookups.singleton (key));
        result.setDisplayName (key.getName()); //or whatever
        result.setIcon (Utilities.loadImage ("path/in/jar/to/image.gif"));
        return result;

ChildFactory can also simplify creating Nodes synchronously, and has the convenience that by using generics, your code can be type safe with respect to key objects. Generally it can be used anywhere Children.Keys would be used (it uses Children.Keys under the hood).