GWT - SimplePanel Widget


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Introduction

The SimplePanel widget represents a base class for panels that contain only one widget.

Class Declaration

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

public class SimplePanel
   extends Panel
      implements HasOneWidget

Class Constructors

Sr.No. Constructor & Description
1

SimplePanel()

Creates an empty panel that uses a DIV for its contents.

2

protected SimplePanel(Element elem)

Creates an empty panel that uses the specified browser element for its contents.

Class Methods

Sr.No. Function name & Description
1

void add(Widget w)

Adds a widget to this panel.

2

protected Element getContainerElement()

Override this method to specify that an element other than the root element be the container for the panel's child widget.

3

Widget getWidget()

Gets the panel's child widget.

4

java.util.Iterator<Widget> iterator()

Gets an iterator for the contained widgets.

5

boolean remove(Widget w)

Removes a child widget.

6

void setWidget(IsWidget w)

Set the only widget of the receiver, replacing the previous widget if there was one.

7

void setWidget(Widget w)

Sets this panel's widget.

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.Panel

  • java.lang.Object

SimplePanel Widget Example

This example will take you through simple steps to show usage of a SimplePanel 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>SimplePanel 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 SimplePanel widget.

package com.tutorialspoint.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.user.client.ui.DecoratorPanel;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.SimplePanel;

public class HelloWorld implements EntryPoint {

   public void onModuleLoad() {
      // Create a Simple Panel
      SimplePanel simplePanel = new SimplePanel();
      Label label = new Label("A Simple Label.");
      //add label to simple panel
      simplePanel.add(label);
	  //set height and width of simple panel
      simplePanel.setHeight("200");
      simplePanel.setWidth("200");

      DecoratorPanel decoratorPanel = new DecoratorPanel();
      decoratorPanel.add(simplePanel);

      // Add the widgets to the root panel.
      RootPanel.get().add(decoratorPanel);
   }	  
}

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 SimplePanel Widget
gwt_layout_panels.htm
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