AP计算机科学A(APcomputer science A)复习备考攻略视频教程
42903 人在学
JPopupMenu的执行看起来有一些别扭:我们必须调用enableEvents()方法并选择鼠标事件代替利用事件接收器。它可能增加一个鼠标接收器但MouseEvent从isPopupTrigger()处不会返回真值——它不知道将激活一个弹出菜单。另外,当我们尝试接收器方法时,它的行为令人不可思议,这或许是鼠标单击活动引起的。在下面的程序例子里一些事件产生了这种弹出行为:
//: Popup.java
// Creating popup menus with Swing
package c13.swing;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Popup extends JPanel {
JPopupMenu popup = new JPopupMenu();
JTextField t = new JTextField(10);
public Popup() {
add(t);
ActionListener al = new ActionListener() {
public void actionPerformed(ActionEvent e){
t.setText(
((JMenuItem)e.getSource()).getText());
}
};
JMenuItem m = new JMenuItem("Hither");
m.addActionListener(al);
popup.add(m);
m = new JMenuItem("Yon");
m.addActionListener(al);
popup.add(m);
m = new JMenuItem("Afar");
m.addActionListener(al);
popup.add(m);
popup.addSeparator();
m = new JMenuItem("Stay Here");
m.addActionListener(al);
popup.add(m);
PopupListener pl = new PopupListener();
addMouseListener(pl);
t.addMouseListener(pl);
}
class PopupListener extends MouseAdapter {
public void mousePressed(MouseEvent e) {
maybeShowPopup(e);
}
public void mouseReleased(MouseEvent e) {
maybeShowPopup(e);
}
private void maybeShowPopup(MouseEvent e) {
if(e.isPopupTrigger()) {
popup.show(
e.getComponent(), e.getX(), e.getY());
}
}
}
public static void main(String args[]) {
Show.inFrame(new Popup(),200,150);
}
} ///:~
相同的ActionListener被加入每个JMenuItem中,使其能从菜单标签中取出文字,并将文字插入JTextField。