GWT - CellTree 小部件

简介

CellTree 小部件表示树的视图。

类声明

以下是 com.google.gwt.user.cellview.client.CellTree 类的声明 −

public class CellTree
   extends AbstractCellTree
      implements HasAnimation, Focusable

类构造函数

类方法

继承的方法

该类继承了以下类的方法 −

• 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 示例

此示例将带您通过简单的步骤展示 GWT 中 CellTree Widget 的使用方法。按照以下步骤更新我们在 GWT - 创建应用程序 一章中创建的 GWT 应用程序 −

以下是修改后的模块描述符src/com.tutorialspoint/HelloWorld.gwt.xml的内容。

<?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>

以下是修改后的样式表文件war/HelloWorld.css的内容。

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;
}

以下是修改后的 HTML 主机文件 war/HelloWorld.html 的内容。

<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>

让我们来看看 Java 文件 src/com.tutorialspoint/HelloWorld.java 的以下内容，它将演示如何使用 CellTree 小部件。

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() {
      
    // 为树创建模型。
    TreeViewModel model = new CustomTreeModel();
    //使用其 BasicResources 获取 CellTree 样式
    //CellTree.Resources res = GWT.create(CellTree.BasicResources.class);
    
    /*
    * 使用模型创建树。我们使用 <code>null</code>
    * 作为根节点的默认值。默认值将
    * 传递给 CustomTreeModel#getNodeInfo();
    */
    CellTree tree = new CellTree(model, null);
    
    tree.setKeyboardSelectionPolicy(KeyboardSelectionPolicy.ENABLED);
    
    // 默认打开第一个播放列表。
    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);
    
    
     // 将小部件添加到根面板。
     RootPanel.get().add(panel);
   }
}

完成所有更改后，让我们像在 GWT - 创建应用程序 一章中一样，在开发模式下编译并运行应用程序。如果您的应用程序一切正常，这将产生以下结果 −

gwt_complex_widgets.html