GWT - Composite Widget
Introduction
The Composite widget is a type of widget that can wrap another widget, hiding the wrapped widget's methods. When added to a panel, a composite behaves exactly as if the widget it wraps had been added. The composite is useful for creating a single widget out of an aggregate of multiple other widgets contained in a single panel.
Class declaration
Following is the declaration for com.google.gwt.user.client.ui.Composite class:
public abstract class Composite extends Widget
Class constructors
| S.N. | Constructor & Description |
|---|---|
| 1 | Composite() |
Class methods
| S.N. | Function name & Description |
|---|---|
| 1 | protected Widget getWidget() Provides subclasses access to the topmost widget that defines this composite. |
| 2 | protected void initWidget(Widget widget) Sets the widget to be wrapped by the composite. |
| 3 | boolean isAttached() Determines whether this widget is currently attached to the browser's document (i.e., there is an unbroken chain of widgets between this widget and the underlying browser document). |
| 4 | protected void onAttach() This method is called when a widget is attached to the browser's document. |
| 5 | void onBrowserEvent(Event event) Fired whenever a browser event is received. |
| 6 | protected void onDetach() This method is called when a widget is detached from the browser's document. |
| 7 | protected void setWidget(Widget widget) Deprecated. Use initWidget(Widget) instead |
Methods inherited
This class inherits methods from the following classes:
com.google.gwt.user.client.ui.UIObject
com.google.gwt.user.client.ui.Widget
java.lang.Object
Composite Widget Example
This example will take you through simple steps to show usage of a Composite Widget in GWT. Follow the following steps to update the GWT application we created in GWT - Create Application chapter:
| Step | Description |
|---|---|
| 1 | Create a project with a name HelloWorld under a package com.tutorialspoint as explained in the GWT - Create Application chapter. |
| 2 | Modify HelloWorld.gwt.xml, HelloWorld.css, HelloWorld.html and HelloWorld.java as explained below. Keep rest of the files unchanged. |
| 3 | Compile and run the application to verify the result of the implemented logic. |
Following is the content of the modified module descriptor src/com.tutorialspoint/HelloWorld.gwt.xml.
<?xml version="1.0" encoding="UTF-8"?> <module rename-to='helloworld'> <!-- Inherit the core Web Toolkit stuff. --> <inherits name='com.google.gwt.user.User'/> <!-- Inherit the default GWT style sheet. --> <inherits name='com.google.gwt.user.theme.clean.Clean'/> <!-- Specify the app entry point class. --> <entry-point class='com.tutorialspoint.client.HelloWorld'/> <!-- Specify the paths for translatable code --> <source path='client'/> <source path='shared'/> </module>
Following is the content of the modified Style Sheet file war/HelloWorld.css.
body{
text-align: center;
font-family: verdana, sans-serif;
}
h1{
font-size: 2em;
font-weight: bold;
color: #777777;
margin: 40px 0px 70px;
text-align: center;
}
Following is the content of the modified HTML host file war/HelloWorld.html.
<html> <head> <title>Hello World</title> <link rel="stylesheet" href="HelloWorld.css"/> <script language="javascript" src="helloworld/helloworld.nocache.js"> </script> </head> <body> <h1>Composite Widget Demonstration</h1> <div id="gwtContainer"></div> </body> </html>
Let us have following content of Java file src/com.tutorialspoint/HelloWorld.java which will demonstrate use of Composite widget.
package com.tutorialspoint.client;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.ui.CheckBox;
import com.google.gwt.user.client.ui.Composite;
import com.google.gwt.user.client.ui.DecoratorPanel;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.TextBox;
import com.google.gwt.user.client.ui.VerticalPanel;
public class HelloWorld implements EntryPoint {
/**
* A composite of a TextBox and a CheckBox that optionally enables it.
*/
private static class OptionalTextBox extends Composite implements
ClickHandler {
private TextBox textBox = new TextBox();
private CheckBox checkBox = new CheckBox();
/**
* Constructs an OptionalTextBox with the given caption
* on the check.
* @param caption the caption to be displayed with the check box
*/
public OptionalTextBox(String caption) {
// Place the check above the text box using a vertical panel.
VerticalPanel panel = new VerticalPanel();
// panel.setBorderWidth(1);
panel.setSpacing(10);
panel.add(checkBox);
panel.add(textBox);
textBox.setWidth("200");
// Set the check box's caption, and check it by default.
checkBox.setText(caption);
checkBox.setValue(true);
checkBox.addClickHandler(this);
DecoratorPanel decoratorPanel = new DecoratorPanel();
decoratorPanel.add(panel);
// All composites must call initWidget() in their constructors.
initWidget(decoratorPanel);
}
public void onClick(ClickEvent event) {
if (event.getSource() == checkBox) {
// When the check box is clicked,
//update the text box's enabled state.
textBox.setEnabled(checkBox.getValue());
}
}
}
public void onModuleLoad() {
// Create an optional text box and add it to the root panel.
OptionalTextBox otb = new OptionalTextBox("Check this to enable me");
RootPanel.get().add(otb);
}
}
Once you are ready with all the changes done, let us compile and run the application in development mode as we did in GWT - Create Application chapter. If everything is fine with your application, this will produce following result:
