GWT - CellBrowser Widget


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Introduction

The CellBrowser widget represents a browsable view of a tree in which only a single node per level may be open at one time.

Class Declaration

Following is the declaration for com.google.gwt.user.cellview.client.CellBrowser<T> class −

public class CellBrowser
   extends AbstractCellTree
      implements ProvidesResize, RequiresResize, HasAnimation

Class Constructors

Sr.No. Constructor & Description
1

CellBrowser(TreeViewModel viewModel, T rootValue)

Construct a new CellBrowser.

2

CellBrowser(TreeViewModel viewModel, T rootValue, CellBrowser.Resources resources)

Construct a new CellBrowser with the specified CellBrowser.Resources.

Class Methods

Sr.No. Function name & Description
1

protected <C> Widget createPager(HasData<C> display)

Create a pager to control the list view.

2

int getDefaultColumnWidth()

Get the default width of new columns.

3

int getMinimumColumnWidth()

Get the minimum width of columns.

4

TreeNode getRootTreeNode()

Get the root TreeNode.

5

boolean isAnimationEnabled()

Returns true if animations are enabled, false if not.

6

void onBrowserEvent(Event event)

Fired whenever a browser event is received.

7

void onResize()

This method must be called whenever the implementor's size has been modified.

8

void setAnimationEnabled(boolean enable)

Enable or disable animations.

9

void setDefaultColumnWidth(int width)

Set the default width of new columns.

10

void set Keyboard Selection Policy (Has Keyboard Selection Policy.Keyboard Selection Policy policy)

Set the HasKeyboardSelectionPolicy.KeyboardSelectionPolicy.

11

void setMinimumColumnWidth(int minWidth)

Set the minimum width of columns.

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

CellBrowser Widget Example

This example will take you through simple steps to show usage of a CellBrowser 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>CellBrowser 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 CellBrowser 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.safehtml.shared.SafeHtmlBuilder;
import com.google.gwt.user.cellview.client.CellBrowser;
import com.google.gwt.user.cellview.client.
HasKeyboardSelectionPolicy.KeyboardSelectionPolicy;
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<Composer>(composers);

         //Create a cell to display a composer.
         Cell<Composer> cell = new AbstractCell<Composer>(){
            @Override
            public void render(Composer value, Object key,
            SafeHtmlBuilder sb) {
               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<Playlist> dataProvider 
         = new ListDataProvider<Playlist>(
         ((Composer) value).getPlaylists());
         Cell<Playlist> cell = new AbstractCell<Playlist>() {
            @Override
            public void render(Playlist value, Object key, 
            SafeHtmlBuilder sb) {
               if (value != null) {
                  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 browser.
      TreeViewModel model = new CustomTreeModel();

      /*
       * Create the browser 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();
       */
      CellBrowser browser = new CellBrowser(model, null);
      browser.setKeyboardSelectionPolicy(KeyboardSelectionPolicy.ENABLED);
      browser.setHeight("200");
      browser.setWidth("630");

      VerticalPanel panel = new VerticalPanel();
      panel.setBorderWidth(1);	    
      panel.add(browser);

      // 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 CellBrowser Widget
gwt_complex_widgets.htm


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