翻译:java中怎样使用树结构(How to Use Trees)(三)

动态改变树

下面的图例展示了一个可以让用户增加,移除节点的树的应用,同时,用户可以对节点文字进行编辑(源代码附后).

你可以对后面的代码进行编译,可以看到一个非常完整的tree的增删改功能演示.

这是tree的初始化代码:

 

通过显式的增加一个tree的样式(model),可以保证tree的样式是DefaultTreeModel的一个实例.这样,我们就可以调用tree模式支持的所有方法.例如,我们可以调用medel的insertNodeInto方法,即使这个方法不是TreeModel接口必须的.

如果要使节点上的文字可编辑,只需调用setEditable(true)方法.当用户编辑完节点,model将产生一个model事件,进而通知事件监听器节点已经修改了.注意:虽然DefaultMutableTreeNode有可以改变节点内容的方法,但是节点内容的改变是通过DefaultTreeModel的方法完成的.另一方面,不会产生tree的model事件,tree的监听器也不会知道数据改变.

为了通报节点的改变,我们需要实现一个TreeModelListener监听器.下面是一个例子:tree model监听器可以发现节点的名字被改变.

 

 

下面的代码演示如何增加一个按钮的事件处理器用来给tree增加一个节点.

 

 

 

上面的代码增加了一个节点,并把它插入tree,如果顺利的话,同时请求上级节点展开,以便新增加的节点可见.为了向model插入一个节点,我们调用了DefaultTreeModel类的insertNodeInto方法.

附:

DynamicTree.java

package dynamicTree;

 

/*

 * This code is based on an example provided by Richard Stanford,

 * a tutorial reader.

 */

 

import java.awt.GridLayout;

import java.awt.Toolkit;

import javax.swing.JPanel;

import javax.swing.JScrollPane;

import javax.swing.JTree;

import javax.swing.tree.DefaultMutableTreeNode;

import javax.swing.tree.DefaultTreeModel;

import javax.swing.tree.MutableTreeNode;

import javax.swing.tree.TreePath;

import javax.swing.tree.TreeSelectionModel;

import javax.swing.event.TreeModelEvent;

import javax.swing.event.TreeModelListener;

 

public class DynamicTree extends JPanel {

    protected DefaultMutableTreeNode rootNode;

    protected DefaultTreeModel treeModel;

    protected JTree tree;

    private Toolkit toolkit = Toolkit.getDefaultToolkit();

 

    public DynamicTree() {

        super(new GridLayout(1,0));

       

        rootNode = new DefaultMutableTreeNode("Root Node");

        treeModel = new DefaultTreeModel(rootNode);

        treeModel.addTreeModelListener(new MyTreeModelListener());

 

        tree = new JTree(treeModel);

        tree.setEditable(true);

        tree.getSelectionModel().setSelectionMode

                (TreeSelectionModel.SINGLE_TREE_SELECTION);

        tree.setShowsRootHandles(true);

 

        JScrollPane scrollPane = new JScrollPane(tree);

        add(scrollPane);

    }

 

    /** Remove all nodes except the root node. */

    public void clear() {

        rootNode.removeAllChildren();

        treeModel.reload();

    }

 

    /** Remove the currently selected node. */

    public void removeCurrentNode() {

        TreePath currentSelection = tree.getSelectionPath();

        if (currentSelection != null) {

            DefaultMutableTreeNode currentNode = (DefaultMutableTreeNode)

                         (currentSelection.getLastPathComponent());

            MutableTreeNode parent = (MutableTreeNode)(currentNode.getParent());

            if (parent != null) {

                treeModel.removeNodeFromParent(currentNode);

                return;

            }

        }

 

        // Either there was no selection, or the root was selected.

        toolkit.beep();

    }

 

    /** Add child to the currently selected node. */

    public DefaultMutableTreeNode addObject(Object child) {

        DefaultMutableTreeNode parentNode = null;

        TreePath parentPath = tree.getSelectionPath();

 

        if (parentPath == null) {

            parentNode = rootNode;

        } else {

            parentNode = (DefaultMutableTreeNode)

                         (parentPath.getLastPathComponent());

        }

 

        return addObject(parentNode, child, true);

    }

 

    public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,

                                            Object child) {

        return addObject(parent, child, false);

    }

 

    public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,

                                            Object child,

                                            boolean shouldBeVisible) {

        DefaultMutableTreeNode childNode =

                new DefaultMutableTreeNode(child);

 

        if (parent == null) {

            parent = rootNode;

        }

 

        treeModel.insertNodeInto(childNode, parent,

                                 parent.getChildCount());

 

        //Make sure the user can see the lovely new node.

        if (shouldBeVisible) {

            tree.scrollPathToVisible(new TreePath(childNode.getPath()));

        }

        return childNode;

    }

 

    class MyTreeModelListener implements TreeModelListener {

        public void treeNodesChanged(TreeModelEvent e) {

            DefaultMutableTreeNode node;

            node = (DefaultMutableTreeNode)

                     (e.getTreePath().getLastPathComponent());

 

            /*

             * If the event lists children, then the changed

             * node is the child of the node we've already

             * gotten.  Otherwise, the changed node and the

             * specified node are the same.

             */

            try {

                int index = e.getChildIndices()[0];

                node = (DefaultMutableTreeNode)

                       (node.getChildAt(index));

            } catch (NullPointerException exc) {}

 

            System.out.println("The user has finished editing the node.");

            System.out.println("New value: " + node.getUserObject());

        }

        public void treeNodesInserted(TreeModelEvent e) {

        }

        public void treeNodesRemoved(TreeModelEvent e) {

        }

        public void treeStructureChanged(TreeModelEvent e) {

        }

    }

}

 

DynamicTreeDemo.java

package dynamicTree;

 

/*

 * This code is based on an example provided by Richard Stanford,

 * a tutorial reader.

 */

 

import java.awt.BorderLayout;

import java.awt.Dimension;

import java.awt.GridLayout;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.tree.DefaultMutableTreeNode;

 

public class DynamicTreeDemo extends JPanel

                             implements ActionListener {

    private int newNodeSuffix = 1;

    private static String ADD_COMMAND = "add";

    private static String REMOVE_COMMAND = "remove";

    private static String CLEAR_COMMAND = "clear";

   

    private DynamicTree treePanel;

 

    public DynamicTreeDemo() {

        super(new BorderLayout());

       

        //Create the components.

        treePanel = new DynamicTree();

        populateTree(treePanel);

 

        JButton addButton = new JButton("Add");

        addButton.setActionCommand(ADD_COMMAND);

        addButton.addActionListener(this);

       

        JButton removeButton = new JButton("Remove");

        removeButton.setActionCommand(REMOVE_COMMAND);

        removeButton.addActionListener(this);

       

        JButton clearButton = new JButton("Clear");

        clearButton.setActionCommand(CLEAR_COMMAND);

        clearButton.addActionListener(this);

 

        //Lay everything out.

        treePanel.setPreferredSize(new Dimension(300, 150));

        add(treePanel, BorderLayout.CENTER);

 

        JPanel panel = new JPanel(new GridLayout(0,1));

        panel.add(addButton);

        panel.add(removeButton);

        panel.add(clearButton);

        add(panel, BorderLayout.LINE_END);

    }

 

    public void populateTree(DynamicTree treePanel) {

        String p1Name = new String("Parent 1");

        String p2Name = new String("Parent 2");

        String c1Name = new String("Child 1");

        String c2Name = new String("Child 2");

 

        DefaultMutableTreeNode p1, p2;

 

        p1 = treePanel.addObject(null, p1Name);

        p2 = treePanel.addObject(null, p2Name);

 

        treePanel.addObject(p1, c1Name);

        treePanel.addObject(p1, c2Name);

 

        treePanel.addObject(p2, c1Name);

        treePanel.addObject(p2, c2Name);

    }

   

    public void actionPerformed(ActionEvent e) {

        String command = e.getActionCommand();

       

        if (ADD_COMMAND.equals(command)) {

            //Add button clicked

            treePanel.addObject("New Node " + newNodeSuffix++);

        } else if (REMOVE_COMMAND.equals(command)) {

            //Remove button clicked

            treePanel.removeCurrentNode();

        } else if (CLEAR_COMMAND.equals(command)) {

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