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:

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);

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.

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) {

 }

}

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.

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

...

public DefaultMutableTreeNode addObject(Object child) {

 DefaultMutableTreeNode parentNode = null;

 TreePath parentPath = tree.getSelectionPath();

 if (parentPath == null) {

 //There's no selection. Default to the root node.

 parentNode = rootNode;

 } else {

 parentNode = (DefaultMutableTreeNode)

 (parentPath.getLastPathComponent());

 }

 return addObject(parentNode, child, true);

}

...

public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,

 Object child,

 boolean shouldBeVisible) {

 DefaultMutableTreeNode childNode =

 new DefaultMutableTreeNode(child);

 ...

 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;

}

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)) {

//Clear button clicked.

treePanel.clear();

}

}

/**

* Create the GUI and show it. For thread safety,

* this method should be invoked from the

* event-dispatching thread.

*/

private static void createAndShowGUI() {

//Make sure we have nice window decorations.

JFrame.setDefaultLookAndFeelDecorated(true);

//Create and set up the window.

JFrame frame = new JFrame("DynamicTreeDemo");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

//Create and set up the content pane.

DynamicTreeDemo newContentPane = new DynamicTreeDemo();

newContentPane.setOpaque(true); //content panes must be opaque

frame.setContentPane(newContentPane);

//Display the window.

frame.pack();

frame.setVisible(true);

}

public static void main(String[] args) {

//Schedule a job for the event-dispatching thread:

//creating and showing this application's GUI.

javax.swing.SwingUtilities.invokeLater(new Runnable() {

public void run() {

createAndShowGUI();

}

});

}

}