In this example we shall show you how to create a ListBox example using the Google Web Toolkit, that is an open source set of tools that allows web developers to create and maintain complex JavaScript front-end applications in Java. A BoxList is a widget that presents a list of choices to the user, either as a list box or as a drop-down list. To create a ListBox example we have performed the following steps:
- The
ListBoxExampleclass implements thecom.google.gwt.core.client.EntryPointinterface to allow the class to act as a module entry point. It overrides itsonModuleLoad()method. - Create a new Horizontal panel.
- Create a ListBox that is a Drop Down List. Add Items to the ListBox.
- Create a new ListBox that displays categories contents. Add Items to this ListBox too.
- Add a ChangeHandler to dropDownList. Override its
onChange(ChangeEvent event)method to handle the change events fire. - Add the boxLists to the HorizontalPanel.
- Add the HorizontalPanel to the
RootPanel, that is the panel to which all other widgets must ultimately be added,
as described in the code snippet below.
package com.javacodegeeks.snippets.enterprise;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.event.dom.client.ChangeEvent;
import com.google.gwt.event.dom.client.ChangeHandler;
import com.google.gwt.user.client.ui.HorizontalPanel;
import com.google.gwt.user.client.ui.ListBox;
import com.google.gwt.user.client.ui.RootPanel;
public class ListBoxExample implements EntryPoint {
// Constants
final String[] Items = { "Item 0", "Item 1", "Item 2" };
final String[] Item0 = { "Item 0,0", "Item 0,1", "Item 0,2" };
final String[] Item1 = { "Item 1,0", "Item 1,1", "Item 1,2" };
final String[] Item2 = { "Item 2,0", "Item 2,1", "Item 2,2" };
@Override
public void onModuleLoad() {
// Create new Horizontal panel
HorizontalPanel hp = new HorizontalPanel();
hp.setSpacing(20);
// Create a ListBox - Drop Down List
final ListBox dropDownList = new ListBox();
// Add Items' categories
for (int i = 0; i < Items.length; i++) {
dropDownList.addItem(Items[i]);
}
// Create new ListBox that displays categories contents
final ListBox contentList = new ListBox();
contentList.setVisibleItemCount(5);
// Initialize the List with data from Item0
for (int i = 0; i < Item0.length; i++) {
contentList.addItem(Item0[i]);
}
// Add ChangeHandler to dropDownList
dropDownList.addChangeHandler(new ChangeHandler() {
@Override
public void onChange(ChangeEvent event) {
// Get the index of the selected Item
int Item = dropDownList.getSelectedIndex();
String[] listData = null;
// Clear the content list
contentList.clear();
// Set content
switch (Item) {
case 0:
listData = Item0;
break;
case 1:
listData = Item1;
break;
case 2:
listData = Item2;
break;
}
for (int i = 0; i < listData.length; i++) {
contentList.addItem(listData[i]);
}
}
});
// Add widgets to Vertical Panel
hp.add(dropDownList);
hp.add(contentList);
// Add Vertical Panel to Root Panel
RootPanel.get().add(hp);
}
}
This was an example of how to create a ListBox example.
