Question

I am trying to create a cell browser , gettign help from GWT Showcase

Here i am creating CellBrowser

        final MultiSelectionModel<MyDTO> selectionModel = new MultiSelectionModel<MyDTO>();

        CellBrowser cellBrowser = new CellBrowser(new ContactTreeViewModel(selectionModel), null);

What i am not getting is that , What is ContactTreeViewModel? I have read the class contacttreeviewmodel in GwtShowcase , but couldnt understand, what is it exactly

thanks for the help

Answer 1

It’s your view model, that is the interface between the tree view and your actual model (in MVC or MVP parlance). The CellBrowser (same for a CellTree) will ask your TreeViewModel for the nodes of the tree (in the form of NodeInfo objects), their children, how to display them (the associated Cell), how to select them (the associated SelectionModel: you can have a tree where you can only select nodes from the 2nd level, and/or only one node per branch at the 2nd level, or any node, or …), and finally how to update them (the ValueUpdater).

Basically (disclaimer: this is a simplification of the process!), each level in the tree is a CellList that a NodeInfo is responsible for. The setDataDisplay associates that CellList with the NodeInfo so that changes to the model can be reflected in the tree, then the Cell, ProvidesKey, SelectionModel and ValueUpdater all have the same behavior as for a CellList. The CellBrowser asks your NodeInfo for them in order to setup the CellList. When expanding a node, the CellBrowser asks your TreeViewModel for the NodeInfo associated to the expanded node and uses it to create a new CellList.

The ContactTreeViewModel from the Showcase is thus a specific implementation of the TreeViewModel to display contacts (the model) as a tree.