《转载》ListCellRenderer interface 实例
在上一节中我们利用ListCellRenderer?? interface在JList中加入Icon图像，而要在JComboBox中加入图像的方法也是一样的。
我们必须实作ListCellRenderer interface所定义的方法getListCellRendererComponent.以下为这个方法的定义：
要先了解ListCellRenderer interface.我们必须由这个interface所定义的方法，将图像画在JComboBox中的每个项目。
ListCellRenderer interface里只定义了一个方法，那就是getListCellRendererComponent,不过这个参数有点多，我们把它列出来
看看:
public Component getListCellRendererComponent(JList list,
?????????????????????????????????????????????? Object value,
?????????????????????????????????????????????? int index,
?????????????????????????????????????????????? boolean isSelected,
?????????????????????????????????????????????? boolean cellHasFocus)
list:即所要画上的图像的JComboBox组件。
value:JComboBox项目值，如JComboBox.getModel().getElementAt(index)所返回的值。
index:为JComboBox项目的索引值，由0开始。
isSelected与cellHasFocus:判断JComboBox中的项目是否有被选取或是有焦点置入。
?? 上面这4个参数会在你设置JComboBox的绘图样式(setCellRenderer())时自动的由JComboBox组件提供，你只要关心怎么控制
getListCellRendererComponent()方法中的4个参数，而无需担心怎么参数传入。
??? 要在JList中加入Icon图像的技巧就是将JComboBox中的每一个项目当作是JLabel,因为JLabel在使用文字与图像上非常的方便，要设置JComboBox的图像，
必须使用setRenderer(ListCellRenderer cellRenderer){注:我们在JList中画上图像是利用JList所提供的setCellRenderer(ListCellRenderer?
cellRenderer)方法,读者请小心}这个方法。我们来看下面这个范例，你就能明白了!
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class JComboBox4{
?? String[] s={"西瓜","苹果","草莓","香蕉","葡萄"};?
?? public JComboBox4(){
?? JFrame f=new JFrame("JComboBox");
?? Container contentPane=f.getContentPane();
??
?? JComboBox combo=new JComboBox(s);
?? combo.setBorder(BorderFactory.createTitledBorder("你最喜欢吃哪些水果?"));
?? combo.setRenderer(new ACellRenderer());
?? combo.setMaximumRowCount(3);
??
?? contentPane.add(combo);
?????? f.pack();
?????? f.show();
?????? f.addWindowListener(new WindowAdapter(){
???? public void windowClosing(WindowEvent e){
?????? System.exit(0);?
???? }
?????? });?????
?? }
?? public static void main(String[] args){
???? new JComboBox4();
?? }
}
?? class ACellRenderer extends JLabel implements ListCellRenderer{
?? ACellRenderer(){
????? setOpaque(true);?
?? }
?? public Component getListCellRendererComponent(JList?? list,
???????????????????????????????????????????????? Object value,
???????????????????????????????????????????????? int index,
???????????????????????????????????????????????? boolean isSelected,
???????????????????????????????????????????????? boolean cellHasFocus){
?????? if (value!=null){
???????? setText(value.toString());
???????? setIcon(new ImageIcon(".\\icons\\fruit"+(index+1)+".jpg"));
?????? }??
?????? if (isSelected){
????????? setBackground(list.getSelectionBackground());
????????? setForeground(list.getSelectionForeground());?
?????? }else{
????????? setBackground(list.getBackground());?
????????? setForeground(list.getForeground());
?????? }????????????????????????????????????
?????? return this;???????
???? }???????????????????????????????????????????????
?? }
???? 各们读者在运行这个程序时会发现，即使JComboBox的选项中有图标，但在选后图标却不会显示在显示列中，原因是在上面程序中
我们以String Array s建立JComboBox:
?????? JComboBox combo=new JComboBox(s);
?????? String Array s里面放的只是水果名称，而并没有图标。当我们使用setRenderer()方法来JComboBox时，只会绘制JComboBox的
选项部份，而最后显示在JComboBox上的值还是以String Array s为依据。因此JComboBox显示列就只会显示文字而已，而不会显示出
图形。要解决这个问题，我们必须改变JComboBox所传入的参数内容，也就是将原来的String Array s更改成具有图形的数据项。在
此我们是利用JComboBox(Object[] items)来建立有图像的JComboBox,我们所传进去的Object Array不应该只有文字，而必须连图标一
并传入。我们修改上个范例修改如下:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class JComboBox5
{
???? String[] s = {"西瓜","苹果","草莓","香蕉","葡萄"};
???? ImageIcon[] icons = new ImageIcon[5];;
????
???? public JComboBox5()
???? {
???????? JFrame f = new JFrame("JComboBox");
???????? Container contentPane = f.getContentPane();
???????? ItemObj[] obj = new ItemObj[5];
????????
???????? for(int i=0; i < 5; i++)
???????? {
???????????? icons[i] = new ImageIcon(".\\icons\\fruit"+(i+1)+".jpg");
???????????? obj[i] = new ItemObj(s[i],icons[i]);
???????? }
????????
???????? JComboBox combo = new JComboBox(obj);//利用ItemObj Array obj当作是JComboBox的参数传入，构造出JComboBox.
???????? combo.setBorder(BorderFactory.createTitledBorder("您喜欢吃哪些水果？"));
???????? combo.setRenderer(new ACellRenderer());
???????? combo.setMaximumRowCount(3);
????????
???????? contentPane.add(combo);
???????? f.pack();
???????? f.show();
???????? f.addWindowListener(new WindowAdapter() {
???????????? public void windowClosing(WindowEvent e) {
???????????????????? System.exit(0);
???????????? }
???????? });
???? }
????
???? public static void main(String args[])
???? {
???????? new JComboBox5();
???? }
}
class ItemObj
{
???? String name;
???? ImageIcon icon;
????
???? public ItemObj(String name, ImageIcon icon){
???????? this.name = name;
???????? this.icon = icon;
???? }
}
????
class ACellRenderer extends JLabel implements ListCellRenderer
{
???? ACellRenderer()
???? {
???????? setOpaque(true);
???? }
????
???? public Component getListCellRendererComponent(JList list,
?????????????????????????????????????????????????? Object value,
?????????????????????????????????????????????????? int index,
?????????????????????????????????????????????????? boolean isSelected,
?????????????????????????????????????????????????? boolean cellHasFocus)
???? {
???????? if (value != null)
???????? {
???????????? setText(((ItemObj)value).name);
???????????? setIcon(((ItemObj)value).icon);
???????? }
???????? if (isSelected) {
???????????? setBackground(list.getSelectionBackground());
???????????? setForeground(list.getSelectionForeground());
???????? }
???????? else {
???????????? setBackground(list.getBackground());
???????????? setForeground(list.getForeground());
???????? }
???????? return this;
???? }????
}
??? 你可以发现，第一栏显示有图标显示出来了。当然你也可以利用ComboBoxModel方式来构造出有图标的JComboBox.我们来看下面
的例子:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class JComboBox6{
?? String[] s={"西瓜","苹果","草莓","香蕉","葡萄"};
?? ImageIcon[] icons=new ImageIcon[5];
?? public JComboBox6(){
???? JFrame f=new JFrame("JComboBox");?
???? Container contentPane=f.getContentPane();
???????? for(int i=0; i < 5; i++)
???????? {
???????????? icons[i] = new ImageIcon(".\\icons\\fruit"+(i+1)+".jpg");
???????? }
???????? ComboBoxModel mode=new AModel();
???????? JComboBox combo=new JComboBox(mode);
???????? combo.setBorder(BorderFactory.createTitledBorder("您喜欢吃哪些水果？"));
???????? combo.setRenderer(new ACellRenderer());
???????? combo.setMaximumRowCount(3);
????????
???????? contentPane.add(combo);
???????? f.pack();
???????? f.show();
???????? f.addWindowListener(new WindowAdapter() {
???????????? public void windowClosing(WindowEvent e) {
???????????????????? System.exit(0);
???????????? }
???????? });
?? }?
?? public static void main(String[] args){
?? new JComboBox6();
?? }
/*我们用JComboBox(ComboBoxModel aModel)来构造图标的JComboBox,因此我们在程序中编写一个继承DefaultComboBoxModel的
ComboBoxModel.
*/
?? class AModel extends DefaultComboBoxModel{
?? AModel(){
????? for (int i=0;i<s.length;i++){
???????? ItemObj obj=new ItemObj(s[i],icons[i]);?
???????? addElement(obj);
????? }?
?? }
?? }
}
class ItemObj
{
???? String name;
???? ImageIcon icon;
????
???? public ItemObj(String name, ImageIcon icon){
???????? this.name = name;
???????? this.icon = icon;
???? }
}
????
class ACellRenderer extends JLabel implements ListCellRenderer
{
???? ACellRenderer()
???? {
???????? setOpaque(true);
???? }
????
???? public Component getListCellRendererComponent(JList list,
?????????????????????????????????????????????????? Object value,
?????????????????????????????????????????????????? int index,
?????????????????????????????????????????????????? boolean isSelected,
?????????????????????????????????????????????????? boolean cellHasFocus)
???? {
???????? if (value != null)
???????? {
???????????? setText(((ItemObj)value).name);
???????????? setIcon(((ItemObj)value).icon);
???????? }
???????? if (isSelected) {
???????????? setBackground(list.getSelectionBackground());
???????????? setForeground(list.getSelectionForeground());
???????? }
???????? else {
???????????? setBackground(list.getBackground());
???????????? setForeground(list.getForeground());
???????? }
???????? return this;
???? }????
}
??? 我们用JComboBox(ComboBoxModel aModel)来构造图标的JComboBox,因此我们在程序中编写一个继承DefaultComboBoxModel的
ComboBoxModel.
