GWT - Button Widget

Introduction

The Button widget represents a standard push button.

Class declaration

Following is the declaration for com.google.gwt.user.client.ui.Button class:

public class Button
   extends ButtonBase

CSS style rules

Following default CSS Style rule will be applied to all the Button widget. You can override it as per your requirements.

.gwt-Button { }

Class constructors

S.N.	Constructor & Description
1	Button() Creates a button with no caption.
2	protected Button(Element element) This constructor may be used by subclasses to explicitly use an existing element.
3	Button(java.lang.String html) Creates a button with the given HTML caption.
4	Button(java.lang.String html, ClickListener listener) Creates a button with the given HTML caption and click listener.

Class methods

S.N.	Function name & Description
1	click() Programmatic equivalent of the user clicking the button.
2	static Button wrap(Element element) Creates a Button widget that wraps an existing <a> element.

Methods inherited

This class inherits methods from the following classes:

com.google.gwt.user.client.ui.UIObject
com.google.gwt.user.client.ui.Widget
com.google.gwt.user.client.ui.FocusWidget
com.google.gwt.user.client.ui.ButtonBase
java.lang.Object

Button Widget Example

This example will take you through simple steps to show usage of a Button 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;
}
.gwt-Button{ 
   color:red;   
}

.gwt-Green-Button{ 
   color:green;   
}
.gwt-Blue-Button { 
   color:blue;   
}

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>Button 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 Button 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.Window;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.VerticalPanel;

public class HelloWorld implements EntryPoint {
   public void onModuleLoad() {
	  
      //create buttons
      Button redButton = new Button("Red");
      Button greenButton = new Button("Green");
      Button blueButton = new Button("Blue");
      
      // use UIObject methods to set button properties.
      redButton.setWidth("100px");
      greenButton.setWidth("100px");
      blueButton.setWidth("100px");
      greenButton.addStyleName("gwt-Green-Button");
      blueButton.addStyleName("gwt-Blue-Button");
      
      //add a clickListener to the button
      redButton.addClickHandler(new ClickHandler() {
         @Override
         public void onClick(ClickEvent event) {
            Window.alert("Red Button clicked!");
         }
      });

      //add a clickListener to the button
      greenButton.addClickHandler(new ClickHandler() {
         @Override
         public void onClick(ClickEvent event) {
            Window.alert("Green Button clicked!");
         }
      });

      //add a clickListener to the button
      blueButton.addClickHandler(new ClickHandler() {
         @Override
         public void onClick(ClickEvent event) {
            Window.alert("Blue Button clicked!");
         }
      });

      // Add button to the root panel.
      VerticalPanel panel = new VerticalPanel();
      panel.setSpacing(10);
      panel.add(redButton);
      panel.add(greenButton);
      panel.add(blueButton);
      
      RootPanel.get("gwtContainer").add(panel);
   }	
}

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:

When you click Click Me button, it will show an alert message Hello World!

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