GWT: How do I populate an initial list for a CellTree using an AsyncDataModel?

I'm using GWT 2.4. I want to create a tree with a fixed set of top level nodes but upon opening each, the data is dynamically retrieved from the server. I have found the AsyncDataProvider class to help me, but I'm having trouble figuring out how to pre-populate the data model with an initial set of values. I have this code (not working) ...

public class CellTreeExample implements EntryPoint {

  /**
   * The model that defines the nodes in the tree.
   */
  private static class CustomTreeModel implements TreeViewModel {

    /**
     * Get the {@link NodeInfo} that provides the children of the specified
     * value.
     */
    public <T> NodeInfo<?> getNodeInfo(T value) {
      /*
       * Create some data in a data provider. Use the parent value as a prefix
       * for the next level.
       */
      AsyncDataProvider<String> dataProvider = new AsyncDataProvider<String>() { 
          @Override
          protected void onRangeChanged(HasData<String> display) {
            // Execute dynamic logic here.
      }
 开发者_JAVA百科     };

      // Set a default set of nodes.
      TextCell textCell = new TextCell();
      final CellList<String> cellList = new CellList<String>(textCell);
      final List<String> rootNodes = getRootNodes();
      cellList.setRowCount(rootNodes.size(), true);
      dataProvider.addDataDisplay(cellList);

      // Return a node info that pairs the data with a cell.
      return new DefaultNodeInfo<String>(dataProvider, new TextCell());
    }

    public boolean isLeaf(Object value) {
        // some logic
    }
  }

  public void onModuleLoad() {
    // Create a model for the tree.
    TreeViewModel model = new CustomTreeModel();

    /*
     * Create the tree using the model. We specify the default value of the
     * hidden root node as "Item 1".
     */
    CellTree tree = new CellTree(model, "Item 1");

    // Add the tree to the root layout panel.
    RootLayoutPanel.get().add(tree);
  }

Nothing appears when I launch my application and I've confirmed that the initial cell list contains 6 items. Any ideas why they are not displaying? Is TextCell not the right type to use when constructing a CellList meant for a CellTree? - Dave

// summarizing pseudocode
public <T> NodeInfo<?> getNodeInfo(final T value) {
  if(value == null) {  // root, return static list of top level nodes
    return new DefaultNodeInfo<String<( 
        new ListDataProvider<String>(Arrays.<String>asList("node1", "node2" ... ));
        , new TextCell());
  }
  else {
    AsyncDataProvider<String> dataProvider = new AsyncDataProvider<String>() { 
      @Override
      protected void onRangeChanged(HasData<String> display) {
        // Execute dynamic logic here - and fetch data from server or wherever
        // call updateRowData() in when data is available
        updateRowData(display.getVisibleRange(), /* List<String> results */);
      }
    }  

    return new DefaultNodeInfo<String>(dataProvider, new TextCell());
  }
}

CellTree via CellTreeNodeView calls setDataDisplay on the returned NodeInfo object with a self created NodeCellList instance, so it looks like it overrides your own CellList and that one never used.

Instead of creating a CellList that displays the values you should return a dataprovider that returns the initial values. I don't fully understand how you use the initial set, just as a placeholder or as the set of root nodes, so I'm not sure how your implemenation would look like, but you might take a look at the GWT CellTree showcase: http://gwt.google.com/samples/Showcase/Showcase.html#!CwCellTree, especially look at the source code of the ContactTreeViewModel class.