级联组合框java

Question

In a java application I want a dialog with several combo boxes, as A, B, and C. A is populated in init components, B is populated when an item in A is selected, and C is populated when B is populated. I know the basic approach, ie, set up a listeners for A & B that populate the next box on Item.SELECTED.

What stumps me is what to do when the B item list is of length 1. With a single item no selection change is possible, so C doesn't get repopulated. Can someone give me a hint?

Thanks?

Ed S

Answer 1

At each level of the tree, check if the current node has no siblings (children of the same parent). If that's the case, fire a selection event programmatically and load the children of the current node.

Answer 2

How about add empty item to B? And C ignore the selection change event when B select empty item.

Answer 3

Problems solved. My problem was assuming that initializing using DefaultComboBoxModel(rootboxitems) would fire the item state change when the box was initialized. It does not; all succeeding boxes must be updated after the initial population and after each selection change. This is easily done if the updating code for each box is put in a separate function so it can be reused.

The example I devised is selection of a car based on the three attributes Make, Model, and Color, eg, "Ford", "Mustang", "Blue". Each Make can have several Models, each with it's own list of Colors.

The dialog & initialization is:

    public CascadeGui(java.awt.Frame parent, boolean modal, Makes aMakes) {
    super(parent, modal);
    ArrayList<Make> makes;
    Make selectedMake;
    Model slectedModel;
    initComponents();
    makes = aMakes.GetMakesArrayList();
    cboMakes.setModel(new javax.swing.DefaultComboBoxModel(makes.toArray(new Make[makes.size()])));
    selectedMake = (Make) cboMakes.getSelectedItem();
    cboModels.setModel(new javax.swing.DefaultComboBoxModel(selectedMake.GetModelsArray()));
    slectedModel = (Model) cboModels.getSelectedItem();
    cboColors.setModel(new javax.swing.DefaultComboBoxModel(slectedModel.GetColorsArray()));

}

This establishes an initial selection of all attributes. The Makes Item State Change event handler is:

    private void cboMakesItemStateChanged(java.awt.event.ItemEvent evt) {                                          
    if (evt.getStateChange() == SELECTED) {
        UpdateModelsCbo();
        UpdateColorsCbo();
    }
}                                         

As you can see, a new section of Make will result in updating of the Models box and then the Colors box. The corresponding code for a Model selection event is:

    private void cboModelsItemStateChanged(java.awt.event.ItemEvent evt) {                                           
    if (evt.getStateChange() == SELECTED) {
        UpdateColorsCbo();
    }
}                                          

I will be glad to share the Netbeans zip file for the example and/or answer questions. At the same time, being somewhat of an novice Java programmer, I would appreciate comments and suggestions for improvement.

Ed