GWT - CellTree Widget

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Introduction

The CellTree widget represents a view of a tree.

Class declaration

Following is the declaration for com.google.gwt.user.cellview.client.CellTree class:

public class CellTree
   extends AbstractCellTree
      implements HasAnimation, Focusable

Class constructors

S.N.Constructor & Description
1CellTree(TreeViewModel viewModel, T rootValue)
Construct a new CellTree.
2CellTree(TreeViewModel viewModel, T rootValue, CellTree.Resources resources)
Construct a new CellTree.

Class methods

S.N.Function name & Description
1protected char getAccessKey()
Get the access key.
2CellTree.NodeAnimation getAnimation()
Get the animation used to open and close nodes in this tree if animations are enabled.
3int getDefaultNodeSize()
Get the default maximum number of children to display under each tree node.
4TreeNode getRootTreeNode()
Get the root TreeNode.
5int getTabIndex()
Gets the widget's position in the tab index.
6boolean isAnimationEnabled()
Returns true if animations are enabled, false if not.
7protected void onBlur()
Called when the keyboard selected node loses focus.
8void onBrowserEvent(Event event)
Fired whenever a browser event is received.
9protected void onFocus()
Called when the keyboard selected node gains focus.
10void setAccessKey(char key)
Sets the widget's 'access key'.
11void setAnimation(CellTree.NodeAnimation animation)
Set the animation used to open and close nodes in this tree.
12void setAnimationEnabled(boolean enable)
Enable or disable animations.
13void setDefaultNodeSize(int defaultNodeSize)
Set the default number of children to display beneath each child node.
14void setFocus(boolean focused)
Explicitly focus/unfocus this widget.
15void setTabIndex(int index)
Sets the widget's position in the tab index.

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.Composite

  • com.google.gwt.user.cellview.client.AbstractCellTree

  • java.lang.Object

CellTree Widget Example

This example will take you through simple steps to show usage of a CellTree Widget in GWT. Follow the following steps to update the GWT application we created in GWT - Create Application chapter:

StepDescription
1Create a project with a name HelloWorld under a package com.tutorialspoint as explained in the GWT - Create Application chapter.
2Modify HelloWorld.gwt.xml, HelloWorld.css, HelloWorld.html and HelloWorld.java as explained below. Keep rest of the files unchanged.
3Compile 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>CellTree 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 CellTree widget.

package com.tutorialspoint.client;

import java.util.ArrayList;
import java.util.List;

import com.google.gwt.cell.client.AbstractCell;
import com.google.gwt.cell.client.Cell;
import com.google.gwt.cell.client.TextCell;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.safehtml.shared.SafeHtmlBuilder;
import com.google.gwt.user.cellview.client.CellTree;
import com.google.gwt.user.cellview.client.
HasKeyboardSelectionPolicy.KeyboardSelectionPolicy;
import com.google.gwt.user.cellview.client.TreeNode;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.VerticalPanel;
import com.google.gwt.view.client.ListDataProvider;
import com.google.gwt.view.client.SingleSelectionModel;
import com.google.gwt.view.client.TreeViewModel;

public class HelloWorld implements EntryPoint {

  /**
  * A list of songs.
  */
  private static class Playlist {
     private final String name;
     private final List<String> songs = new ArrayList<String>();

     public Playlist(String name) {
       this.name = name;
     }

      /**
      * Add a song to the playlist.
      * 
      * @param name the name of the song
      */
      public void addSong(String name) {
         songs.add(name);
      }

      public String getName() {
         return name;
      }

      /**
      * Return the list of songs in the playlist.
      */
      public List<String> getSongs() {
         return songs;
      }
   }

   /**
   * A composer of classical music.
   */
   private static class Composer {
      private final String name;
      private final List<Playlist> playlists = new ArrayList<Playlist>();

      public Composer(String name) {
         this.name = name;
      }

      /**
      * Add a playlist to the composer.
      * 
      * @param playlist the playlist to add
      */
      public Playlist addPlaylist(Playlist playlist) {   
         playlists.add(playlist);
         return playlist;
      }

      public String getName() {
         return name;
      }

      /**
      * Return the rockin' playlist for this composer.
      */
      public List<Playlist> getPlaylists() {
         return playlists;
      }
   }

   /**
   * The model that defines the nodes in the tree.
   */
   private static class CustomTreeModel implements TreeViewModel {

   private final List<Composer> composers;

   /**
   * This selection model is shared across all leaf nodes. 
   * A selection model can also be shared across all nodes 
   * in the tree, or each set of child nodes can have 
   * its own instance. This gives you flexibility to 
   * determine how nodes are selected.
   */
   private final SingleSelectionModel<String> selectionModel 
   = new SingleSelectionModel<String>();

      public CustomTreeModel() {
         // Create a database of information.
         composers = new ArrayList<Composer>();

         // Add compositions by Beethoven.
         {
            Composer beethoven = new Composer("Beethoven");
            composers.add(beethoven);
   
            Playlist concertos = beethoven.addPlaylist(
            new Playlist("Concertos"));
            concertos.addSong("No. 1 - C");
            concertos.addSong("No. 2 - B-Flat Major");
            concertos.addSong("No. 3 - C Minor");
            concertos.addSong("No. 4 - G Major");
            concertos.addSong("No. 5 - E-Flat Major");

            Playlist quartets = beethoven.addPlaylist(
            new Playlist("Quartets"));
            quartets.addSong("Six String Quartets");
            quartets.addSong("Three String Quartets");
            quartets.addSong("Grosse Fugue for String Quartets");

            Playlist sonatas = beethoven.addPlaylist(
            new Playlist("Sonatas"));
            sonatas.addSong("Sonata in A Minor");
            sonatas.addSong("Sonata in F Major");

            Playlist symphonies = beethoven.addPlaylist(
            new Playlist("Symphonies"));
            symphonies.addSong("No. 2 - D Major");
            symphonies.addSong("No. 2 - D Major");
            symphonies.addSong("No. 3 - E-Flat Major");
            symphonies.addSong("No. 4 - B-Flat Major");
            symphonies.addSong("No. 5 - C Minor");
            symphonies.addSong("No. 6 - F Major");
            symphonies.addSong("No. 7 - A Major");
            symphonies.addSong("No. 8 - F Major");
            symphonies.addSong("No. 9 - D Minor");
         }

         // Add compositions by Brahms.
         {
            Composer brahms = new Composer("Brahms");
            composers.add(brahms);
            Playlist concertos = brahms.addPlaylist(
            new Playlist("Concertos"));
            concertos.addSong("Violin Concerto");
            concertos.addSong("Double Concerto - A Minor");
            concertos.addSong("Piano Concerto No. 1 - D Minor");
            concertos.addSong("Piano Concerto No. 2 - B-Flat Major");

            Playlist quartets = brahms.addPlaylist(
            new Playlist("Quartets"));
            quartets.addSong("Piano Quartet No. 1 - G Minor");
            quartets.addSong("Piano Quartet No. 2 - A Major");
            quartets.addSong("Piano Quartet No. 3 - C Minor");
            quartets.addSong("String Quartet No. 3 - B-Flat Minor");

            Playlist sonatas = brahms.addPlaylist(
            new Playlist("Sonatas"));
            sonatas.addSong("Two Sonatas for Clarinet - F Minor");
            sonatas.addSong("Two Sonatas for Clarinet - E-Flat Major");

            Playlist symphonies = brahms.addPlaylist(
            new Playlist("Symphonies"));
            symphonies.addSong("No. 1 - C Minor");
            symphonies.addSong("No. 2 - D Minor");
            symphonies.addSong("No. 3 - F Major");
            symphonies.addSong("No. 4 - E Minor");
         }

         // Add compositions by Mozart.
         {
            Composer mozart = new Composer("Mozart");
            composers.add(mozart);
            Playlist concertos = mozart.addPlaylist(
            new Playlist("Concertos"));
            concertos.addSong("Piano Concerto No. 12");
            concertos.addSong("Piano Concerto No. 17");
            concertos.addSong("Clarinet Concerto");
            concertos.addSong("Violin Concerto No. 5");
            concertos.addSong("Violin Concerto No. 4");
         }
      }

      /**
      * Get the {@link NodeInfo} that provides the children of the 
      * specified value.
      */
      public <T> NodeInfo<?> getNodeInfo(T value) {
         if (value == null) {
            // LEVEL 0.
            // We passed null as the root value. Return the composers.

            // Create a data provider that contains the list of composers.
            ListDataProvider<Composer> dataProvider 
            = new ListDataProvider<HelloWorld.Composer>(
            composers);

            // Create a cell to display a composer.
            Cell<HelloWorld.Composer> cell 
            = new AbstractCell<HelloWorld.Composer>() {
               @Override
               public void render(Composer value, Object key,
               SafeHtmlBuilder sb) {
                  if (value != null) {
                	 sb.appendHtmlConstant("    "); 
                     sb.appendEscaped(value.getName());
                  }				
               }
            };

            // Return a node info that pairs the data provider and the cell.
            return new DefaultNodeInfo<Composer>(dataProvider, cell);
         } else if (value instanceof Composer) {
            // LEVEL 1.
            // We want the children of the composer. Return the playlists.
            ListDataProvider<HelloWorld.Playlist> dataProvider
            = new ListDataProvider<HelloWorld.Playlist>(
            ((Composer) value).getPlaylists());
            Cell<HelloWorld.Playlist> cell = 
            new AbstractCell<HelloWorld.Playlist>() {
               @Override
               public void render(Playlist value, Object key,
               SafeHtmlBuilder sb) {
                  if (value != null) {        
                	 sb.appendHtmlConstant("    "); 
                     sb.appendEscaped(value.getName());
                  }
               }
            };
            return new DefaultNodeInfo<Playlist>(dataProvider, cell);
        } else if (value instanceof Playlist) {
            // LEVEL 2 - LEAF.
            // We want the children of the playlist. Return the songs.
            ListDataProvider<String> dataProvider 
            = new ListDataProvider<String>(
            ((Playlist) value).getSongs());

            // Use the shared selection model.
            return new DefaultNodeInfo<String>(dataProvider, new TextCell(),
            selectionModel, null);
         }

         return null;
      }

      /**
      * Check if the specified value represents a leaf node. 
      * Leaf nodes cannot be opened.
      */
      public boolean isLeaf(Object value) {
      // The leaf nodes are the songs, which are Strings.
      if (value instanceof String) {
         return true;
      }
      return false;
      }
   }

   public void onModuleLoad() {
      // Create a model for the tree.
      TreeViewModel model = new CustomTreeModel();
      //Get CellTree style using its BasicResources	   
      //CellTree.Resources res = GWT.create(CellTree.BasicResources.class);
      /*
      * Create the tree using the model. We use <code>null</code> 
      * as the default value of the root node. The default value will 
      * be passed to CustomTreeModel#getNodeInfo();
      */
      CellTree tree = new CellTree(model, null);
   
      tree.setKeyboardSelectionPolicy(KeyboardSelectionPolicy.ENABLED);

      // Open the first playlist by default.
      TreeNode rootNode = tree.getRootTreeNode();
      TreeNode firstPlaylist = rootNode.setChildOpen(0, true);
      firstPlaylist.setChildOpen(0, true);

      VerticalPanel panel = new VerticalPanel();
	  panel.setBorderWidth(1);	    
	  panel.setWidth("300");
	  panel.add(tree);
	    

	 // Add the widgets to the root panel.
	 RootPanel.get().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 CellTree Widget

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