在JTable中实现单元格鼠标悬停效果
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.java
package 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
