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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
Sr.No. | Constructor & Description |
---|---|
1 |
Composite() |
Class Methods
Sr.No. | 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 −
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