翻译:java中怎样使用树结构(How to Use Trees)(三)

[/b]动态改变树[/b][/b]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();
}});
}}