GWT - Hidden Widget

Introduction

The Hidden widget represents a hidden field in an HTML form.

Class Declaration

Following is the declaration for com.google.gwt.user.client.ui.Hidden class −

public class Hidden
   extends Widget
      implements HasName

Class Constructors

Sr.No.	Constructor & Description
1	Hidden() Constructor for Hidden.
2	Hidden(Element element) This constructor may be used by subclasses to explicitly use an existing element.
3	Hidden(java.lang.String name) Constructor for Hidden.
4	Hidden(java.lang.String name, java.lang.String value) Constructor for Hidden.

Class Methods

Sr.No.	Function name & Description
1	java.lang.String getDefaultValue() Gets the default value of the hidden field.
2	java.lang.String getID() Gets the id of the hidden field.
3	java.lang.String getName() Gets the name of the hidden field.
4	java.lang.String getValue() Gets the value of the hidden field.
5	void setDefaultValue(java.lang.String defaultValue) Sets the default value of the hidden field.
6	void setID(java.lang.String id) Sets the id of the hidden field.
7	void setName(java.lang.String name) Sets the name of the hidden field.
8	void setValue(java.lang.String value) Sets the value of the hidden field.
9	static Hidden wrap(Element element) Creates a Hidden widget that wraps an existing <input type='hidden'> 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
java.lang.Object

Hidden Widget Example

This example will take you through simple steps to show usage of a Hidden 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>Hidden 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 Hidden 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.Hidden;
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 {
   public void onModuleLoad() {
      //create textboxes
      final TextBox textBox = new TextBox(); 
      textBox.setWidth("275");
      Button button1 = new Button("Set Value of Hidden Input");
      Button button2 = new Button("Get Value of Hidden Input");
      final Hidden hidden = new Hidden();

      button1.addClickHandler(new ClickHandler() {
         @Override
         public void onClick(ClickEvent event) {
            hidden.setValue(textBox.getValue());
            Window.alert("Value of Hidden Widget Updated!");
         }
      });

      button2.addClickHandler(new ClickHandler() {
         @Override
         public void onClick(ClickEvent event) {
            Window.alert("Value of Hidden Widget: " + hidden.getValue());
         }
      });

      // Add widgets to the root panel.
      VerticalPanel panel = new VerticalPanel();
      panel.setSpacing(10);
      panel.add(textBox);
      panel.add(button1);
      panel.add(hidden);
      panel.add(button2);

      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 −

gwt_form_widgets.htm