个性化树显示
如前所述,树的每一个节点通常有一个图标和一些文字.你可以定制这些图标和文字.
一个tree通常会展示一些特殊外观来显示节点间的联系.你可以通过简单的几步来自定义这些外观样式.首先,你可以用tree.setRootVisible(true)来显示根节点,用tree.setRootVisible(false)来隐藏根节点.然后,通过调用tree.setShowsRootHandles(true),可以让tree的顶级节点—根节点(如果可见)或者其子节点—展开或者收缩.最后,如果你采用java风格样式,你还可以自定义是否显示线条来展示树节点间的关系.
默认的,java风格会在节点间画出一个带直角的直线.通过设置Tree.lineStyle属性,你可以指定不同的样式.例如,如果采用java风格,通过调用如下代码,可以用横线来组织各节点.
tree.putClientProperty("JTree.lineStyle", "Horizontal");
如果不想显示任何线条,则可以用如下代码:
tree.putClientProperty("JTree.lineStyle", "None");
不管风格如何,节点的默认图标由以下条件决定:节点是否是叶子
节点(leaf node),节点是否展开.例如:在windows风格下,叶子节点
的默认图标是一个点;在java风格下,叶子节点的默认图标却是一个纸
张图标.在我们展示的所有风格样式中,分支节点的默认图标是一个文
件夹图标.在展开或者收缩分支节点时,有些节点图标也有可能显示略
有不同.
我们可以非常容易的改变默认的图标.首先,增加一个DefaultTreeCellRenderer
的实例;然后,调用一下方法来指定你要采用的图标:
setLeafIcon(设置叶子节点),setOpenIcon(设置展开的分支节点),
setClosedIcon (设置收缩的分支节点).如果你不想让任何节点有图标,只需设置每个图标为null就可以了.一旦设置好图标,就可以用tree的
setCellRenderer方法来指定DefaultTreeCellRenderer渲染节点.
下面是一个例子,选自TreeIconDemo.java(后附其源代码)ImageIcon leafIcon = createImageIcon("images/middle.gif");
if (leafIcon != null) {
DefaultTreeCellRenderer renderer =
new DefaultTreeCellRenderer();
renderer.setLeafIcon(leafIcon);
tree.setCellRenderer(renderer);
}
如果你想更好的控制节点图标或者你想提供一个提示信息,那么你需要增加一个DefaultTreeCellRenderer的子类并且重载getTreeCellRendererComponen方法.因为DefaultTreeCellRenderer是JLabel的子类,所以你可以用JLabel的所有方法---比如setIcon----来个性化DefaultTreeCellRenderer.下面的代码,来自TreeIconDemo2.java,,增加一个cellrenderer,通
过判断节点文字中是否包含”tutorial”来改变叶子节点图标.renderer也
可以改变提示文字,用粗体显示.
//...where the tree is initialized:
//Enable tool tips.
ToolTipManager.sharedInstance().registerComponent(tree);
ImageIcon tutorialIcon = createImageIcon("images/middle.gif");
if (tutorialIcon != null) {
tree.setCellRenderer(new MyRenderer(tutorialIcon));
}
...
class MyRenderer extends DefaultTreeCellRenderer {
Icon tutorialIcon;
public MyRenderer(Icon icon) {
tutorialIcon = icon;
}
public Component getTreeCellRendererComponent(
JTree tree,
Object value,
boolean sel,
boolean expanded,
boolean leaf,
int row,
boolean hasFocus) {
super.getTreeCellRendererComponent(
tree, value, sel,
expanded, leaf, row,
hasFocus);
if (leaf && isTutorialBook(value)) {
setIcon(tutorialIcon);
setToolTipText("This book is in the Tutorial series.");
} else {
setToolTipText(null); //no tool tip
}
return this;
}
protected boolean isTutorialBook(Object value) {
DefaultMutableTreeNode node =
(DefaultMutableTreeNode)value;
BookInfo nodeInfo =
(BookInfo)(node.getUserObject());
String title = nodeInfo.bookName;
if (title.indexOf("Tutorial") >= 0) {
return true;
}
return false;
}
}
你也许会奇怪: cell renderer是如何工作的.当一个tree绘出每一个节点时,既不是JTree,也不是风格样式包含执行绘制节点的代码.
相反,tree是通过调用cellrenderer的绘制代码来完成节点的绘制的.
例如:为了绘制一个含有字符串"The Java Programming Language"的
节点,tree会让它的cellrenderer返回一个组件对象,此组件对象可以
绘制一个包含"The Java Programming Language"字符串的节点.如果这
个cellrenderer是DefaultTreeCellRenderer,那么,它会返回一个标签对象,
此标签对象上绘制了一个包含此字符串的一个叶子节点. Cellrenderer只能用来绘制节点,它不能处理事件.如果你想在tree中增加事件处理,你需要注册你的事件处理器.
TreeIconDemo.java:/**
* A 1.4 application that requires the following additional files:
* TreeDemoHelp.html
* arnold.html
* bloch.html
* chan.html
* jls.html
* swingtutorial.html
* tutorial.html
* tutorialcont.html
* vm.html
*/
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreeSelectionModel;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.DefaultTreeCellRenderer;
import javax.swing.ImageIcon;
import java.net.URL;
import java.io.IOException;
import java.awt.Dimension;
import java.awt.GridLayout;
public class TreeIconDemo extends JPanel
implements TreeSelectionListener {
private JEditorPane htmlPane;
private JTree tree;
private URL helpURL;
private static boolean DEBUG = false;
public TreeIconDemo() {
super(new GridLayout(1,0));
//Create the nodes.
DefaultMutableTreeNode top =
new DefaultMutableTreeNode("The Java Series");
createNodes(top);
//Create a tree that allows one selection at a time.
tree = new JTree(top);
tree.getSelectionModel().setSelectionMode
(TreeSelectionModel.SINGLE_TREE_SELECTION);
//Set the icon for leaf nodes.
ImageIcon leafIcon = createImageIcon("images/middle.gif");
if (leafIcon != null) {
DefaultTreeCellRenderer renderer = new DefaultTreeCellRenderer();
renderer.setLeafIcon(leafIcon);
tree.setCellRenderer(renderer);
} else {
System.err.println("Leaf icon missing; using default.");
}
//Listen for when the selection changes.
tree.addTreeSelectionListener(this);
//Create the scroll pane and add the tree to it.
JScrollPane treeView = new JScrollPane(tree);
//Create the HTML viewing pane.
htmlPane = new JEditorPane();
htmlPane.setEditable(false);
initHelp();
JScrollPane htmlView = new JScrollPane(htmlPane);
//Add the scroll panes to a split pane.
JSplitPane splitPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT);
splitPane.setTopComponent(treeView);
splitPane.setBottomComponent(htmlView);
Dimension minimumSize = new Dimension(100, 50);
htmlView.setMinimumSize(minimumSize);
treeView.setMinimumSize(minimumSize);
splitPane.setDividerLocation(100); //XXX: ignored in some releases
//of Swing. bug 4101306
//workaround for bug 4101306:
//treeView.setPreferredSize(new Dimension(100, 100));
splitPane.setPreferredSize(new Dimension(500, 300));
//Add the split pane to this panel.
add(splitPane);
}
/** Required by TreeSelectionListener interface. */
public void valueChanged(TreeSelectionEvent e) {
DefaultMutableTreeNode node = (DefaultMutableTreeNode)
tree.getLastSelectedPathComponent();
if (node == null) return;
Object nodeInfo = node.getUserObject();
if (node.isLeaf()) {
BookInfo book = (BookInfo)nodeInfo;
displayURL(book.bookURL);
if (DEBUG) {
System.out.print(book.bookURL + ": /n ");
}
} else {
displayURL(helpURL);
}
if (DEBUG) {
System.out.println(nodeInfo.toString());
}
}
private class BookInfo {
public String bookName;
public URL bookURL;
public BookInfo(String book, String filename) {
bookName = book;
bookURL = TreeIconDemo.class.getResource(filename);
if (bookURL == null) {
System.err.println("Couldn't find file: "
+ filename);
}
}
public String toString() {
return bookName;
}
}
private void initHelp() {
String s = "TreeDemoHelp.html";
helpURL = TreeIconDemo.class.getResource(s);
if (helpURL == null) {
System.err.println("Couldn't open help file: " + s);
} else if (DEBUG) {
System.out.println("Help URL is " + helpURL);
}
displayURL(helpURL);
}
private void displayURL(URL url) {
try {
if (url != null) {
htmlPane.setPage(url);
} else { //null url
htmlPane.setText("File Not Found");
if (DEBUG) {
System.out.println("Attempted to display a null URL.");
}
}
} catch (IOException e) {
System.err.println("Attempted to read a bad URL: " + url);
}
}
private void createNodes(DefaultMutableTreeNode top) {
DefaultMutableTreeNode category = null;
DefaultMutableTreeNode book = null;
category = new DefaultMutableTreeNode("Books for Java Programmers");
top.add(category);
//original Tutorial
book = new DefaultMutableTreeNode(new BookInfo
("The Java Tutorial: A Short Course on the Basics",
"tutorial.html"));
category.add(book);
//Tutorial Continued
book = new DefaultMutableTreeNode(new BookInfo
("The Java Tutorial Continued: The Rest of the JDK",
"tutorialcont.html"));
category.add(book);
//JFC Swing Tutorial
book = new DefaultMutableTreeNode(new BookInfo
("The JFC Swing Tutorial: A Guide to Constructing GUIs",
"swingtutorial.html"));
category.add(book);
//Bloch
book = new DefaultMutableTreeNode(new BookInfo
("Effective Java Programming Language Guide",
"bloch.html"));
category.add(book);
//Arnold/Gosling
book = new DefaultMutableTreeNode(new BookInfo
("The Java Programming Language", "arnold.html"));
category.add(book);
//Chan
book = new DefaultMutableTreeNode(new BookInfo
("The Java Developers Almanac",
"chan.html"));
category.add(book);
category = new DefaultMutableTreeNode("Books for Java Implementers");
top.add(category);
//VM
book = new DefaultMutableTreeNode(new BookInfo
("The Java Virtual Machine Specification",
"vm.html"));
category.add(book);
//Language Spec
book = new DefaultMutableTreeNode(new BookInfo
("The Java Language Specification",
"jls.html"));
category.add(book);
}
/** Returns an ImageIcon, or null if the path was invalid. */
protected static ImageIcon createImageIcon(String path) {
java.net.URL imgURL = TreeIconDemo.class.getResource(path);
if (imgURL != null) {
return new ImageIcon(imgURL);
} else {
System.err.println("Couldn't find file: " + path);
return null;
}
}
/**
* 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("TreeIconDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
TreeIconDemo newContentPane = new TreeIconDemo();
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();
}
});
}
}
TreeIconDemo2.java/**
* A 1.4 application that requires the following additional files:
* TreeDemoHelp.html
* arnold.html
* bloch.html
* chan.html
* jls.html
* swingtutorial.html
* tutorial.html
* tutorialcont.html
* vm.html
*/
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreeSelectionModel;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.DefaultTreeCellRenderer;
import javax.swing.ToolTipManager;
import javax.swing.ImageIcon;
import javax.swing.Icon;
import java.net.URL;
import java.io.IOException;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.Component;
public class TreeIconDemo2 extends JPanel
implements TreeSelectionListener {
private JEditorPane htmlPane;
private JTree tree;
private URL helpURL;
private static boolean DEBUG = false;
public TreeIconDemo2() {
super(new GridLayout(1,0));
//Create the nodes.
DefaultMutableTreeNode top =
new DefaultMutableTreeNode("The Java Series");
createNodes(top);
//Create a tree that allows one selection at a time.
tree = new JTree(top);
tree.getSelectionModel().setSelectionMode
(TreeSelectionModel.SINGLE_TREE_SELECTION);
//Enable tool tips.
ToolTipManager.sharedInstance().registerComponent(tree);