在JTable中实现单元格鼠标悬停效果
类别: JAVA教程 
在Google上搜索实现这种效果的方法，只搜到一个网页，是国外的，一看，还得要给钱注册！俗话说，自力更生，艰苦奋斗，就自己想了法子，拿来分享。衷心请各位大虾指点指点不足
我写了个程序，里面用到一个JTable，本着MVC的精神，而且考虑到单元格可能不是简简单单一个Label能表现的，就写了个表格渲染器的类，叫NoteLabelRenderer
代码如下：
//NoteLabelRenderer.javapackage com.component;
import javax.swing.*;import javax.swing.table.*;
import java.awt.*;
import com.data.Note;
/** * To render the cells showing the note * @author Allen Chue * */public class NoteLabelRenderer extends JPanel implements TableCellRenderer {
public static ImageIcon ATTACH_ICON=new ImageIcon("res/attach.gif"); public static ImageIcon BLANK_ICON=new ImageIcon("res/blank.gif"); private JLabel icon=new JLabel(); private JLabel content=new JLabel(); private JLabel attach=new JLabel(); private String contentText,title; public NoteLabelRenderer() { super(); setLayout(new BorderLayout()); icon.setOpaque(true); content.setOpaque(true); attach.setOpaque(true); icon.setHorizontalAlignment(SwingConstants.CENTER); icon.setVerticalAlignment(SwingConstants.CENTER); content.setVerticalAlignment(SwingConstants.NORTH); attach.setHorizontalAlignment(SwingConstants.CENTER); attach.setVerticalAlignment(SwingConstants.CENTER); add(icon,BorderLayout.WEST); add(content,BorderLayout.CENTER); add(attach,BorderLayout.EAST); setSize(getPreferredSize()); } /** * Returns the component used for drawing the cell. This method is * used to configure the renderer appropriately before drawing. * * @param table the <code>JTable</code> that is asking the * renderer to draw; can be <code>null</code> * @param value the value of the cell to be rendered. It is * up to the specific renderer to interpret * and draw the value. For example, if * <code>value</code> * is the string "true", it could be rendered as a * string or it could be rendered as a check * box that is checked. <code>null</code> is a * valid value * @param isSelected true if the cell is to be rendered with the * selection highlighted; otherwise false * @param hasFocus if true, render cell appropriately. For * example, put a special border on the cell, if * the cell can be edited, render in the color used * to indicate editing * @param row the row index of the cell being drawn. When * drawing the header, the value of * <code>row</code> is -1 * @param column the column index of the cell being drawn */ public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus, int row, int column) { changeBackground(isSelected); setNoteText((Note)value,isSelected); return this; } private void changeBackground(boolean isSelected) { Color selectedColor=new Color(160,231,160); if (isSelected) { icon.setBackground(selectedColor); content.setBackground(selectedColor); attach.setBackground(selectedColor); } else { icon.setBackground(null); content.setBackground(null); attach.setBackground(null); } } /** * Show the note according to a note * @param n The <code>Note</code> * @param flag A flag variable. True for emphasizing the the * contents, while false for showing it normally */ private void setNoteText(Note n, boolean flag) { String color=flag?"#ffffff":"#000000"; /* ************************ *****Set Icon Area****** ************************ */ icon.setIcon(n.getIcon()); /* ************************ ****Set Content Area**** ************************ */ title=n.getTitle(); contentText=n.getContent(); if (contentText.length()>120) { contentText=contentText.substring(0,115)+"..."; } content.setText("<html><font" + " color=#116677>"+title+"</font><br>" + "<font color="+color+">"+contentText+"</font></html>"); /* *********************** ***Set Attach Area***** *********************** */ if (n.getAttach() != null) { attach.setIcon(ATTACH_ICON); } else { attach.setIcon(BLANK_ICON); } } public String getContent() { return this.contentText; } public String getTitle() { return this.title; }}
这是个备忘的程序，一些有Note字眼的不用关心。
这个NoteLableRenderer继承了JPanel，是为了更好地对其中一些组件进行布局的控制（在这里，每个单元格里有三个JLabel），TableCellRender接口是必须要实现的可以看到，实现鼠标点击单元格改变文字颜色和单元格（也就是一个JPanel）背景色并不难，只需要在getTableCellRendererComponent方法中判断传入的参数isSelected是否为true，然后对组件属性重新设置，返回修改过的Component即可。JTable在鼠标点击单元格时会重画表格，于是改变后的单元格即可显示出来。
我还想要实现单元格的悬停效果，也就是说，当鼠标移动至某个单元格上方时，该单元格可以变化颜色或者加个边框来突出显示，就想JButton可以设置RollOverIcon一样。我想当然地在这个渲染器里添加了鼠标监听，然而测试确发现不行... 经过一番查阅、思考，我终于将解决的方法从单元格渲染器上转至JTable本身来，因为我发现JTable里竟然有个rowAtPoint(Point point)方法（高手可不要笑我啊）！于是，我就在表格上监听鼠标动作事件，在mouseMoved(MouseEvent e)方法中用int row=this.rowAt(e.getPoint())得到鼠标移动时当前鼠标在哪一行。这样的话，至少是迈了一大步，接下来的问题就是如何对鼠标下面的单元格进行属性的修改。
经过查看JTable的源码，发现里面有个public Component prepareRenderer方法调用了单元格渲染器里的getTableCellRenderer方法，用于在绘制表格时准备好单元格内放置的组件。既然它是public的，我就重载了这个方法，并使用了个自己感觉有点笨的方法，表格中加了个Vector，存储每个单元格是否在鼠标下面的信息（用Boolean），也就是说，每一时刻这个Vector中只有一个为true（同一时刻，只能有一个单元格在鼠标下面）,其余为false，同时保持Vector的size与单元格行数相同。重载的prepareRenderer方法体如下：
/** * This method overides the super one, in order to * add rollover effects to the <code>JTable</code> * A <code>Vector</code> stores information about * whether the cell is beneath the mouse. If the value * corresponding to the cell is true, this method will * return a <code>Component</code> with the border modified; * while false, the <code>Renderer</code> will be returned * unchanged after calling the super method */ public Component prepareRenderer(TableCellRenderer renderer, int row, int column) { Component comp = super.prepareRenderer(renderer, row, column); if (((Boolean)flagMouseOver.get(row)).booleanValue()) { ((JComponent)comp).setBorder(BorderFactory.createLineBorder(Color.GRAY,1)); return comp; } else { ((JComponent)comp).setBorder(null); return comp; } }
flagMouseOver即为保存单元格状态的Vector。而mouseMoved方法如下
public void mouseMoved(MouseEvent e) {//Add rollover effects int row=this.rowAtPoint(e.getPoint()); if (mouseAtRow == -1) { //Init variable mouseAtRow mouseAtRow=row; flagMouseOver.set(mouseAtRow,new Boolean(true)); //System.out.println("Mouse first moves to row "+(row+1)); repaint(); revalidate(); } else if (row != mouseAtRow) {//The mouse has moved to a new row //Clear the border flagMouseOver.set(mouseAtRow,new Boolean(false)); //Set new row\'s border flagMouseOver.set(row,new Boolean(true)); //System.out.println("Mouse moves from row "+(mouseAtRow+1)+" to row "+(row+1)); repaint(); revalidate(); mouseAtRow=row; } }
mouseAtRow为一个int类型的变量，存储鼠标移动前在哪一行。当鼠标移动时，获得当前鼠标在哪一行（表格仅有一列），然后与mouseAtRow比较，若变化了，说明鼠标到了新的一行，同时更新flagMouseOver内的数据，紧接着用repaint和revalidate方法更新表格，实现了表格GUI的变化。这里悬停效果是添加边框，当然也可以改背景等等。
这是我的经历，希望有人提出意见，我非常欢迎！
Allen Chue
