hierlistenerdemo.java

来自「《java事件处理指南》一书的代码,好东西」· Java 代码 · 共 105 行

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class HierListenerDemo extends JFrame implements ActionListener
{
   private JButton button, removePanelButton, removeButton;
   private JPanel centerPanel;
   private JTextField jtf;

   public HierListenerDemo()
   {
/*  A JButton is placed on a JFrame.  The button registers   */
/*  a HierarchyListener.                                     */

      button = new JButton("Button");
      button.setBorder(BorderFactory.createRaisedBevelBorder());
      button.addHierarchyListener(new HierListener());

/*  Two more buttons are placed on the JFrame.  These buttons   */
/*  are used to change the visibility of the center panel.      */
/*  These buttons register an ActionListener.                   */

      removePanelButton = new JButton("Hide Panel");
      removePanelButton.setActionCommand("hide");
      removePanelButton.setBorder(BorderFactory.createRaisedBevelBorder());
      removePanelButton.addActionListener(this);

      removeButton = new JButton("Show Panel");
      removeButton.setActionCommand("show");
      removeButton.setBorder(BorderFactory.createRaisedBevelBorder());
      removeButton.addActionListener(this);

      jtf = new JTextField(15);
      jtf.setEditable(false);

      centerPanel = new JPanel();
      centerPanel.setName("center");
      centerPanel.add(button);

      JPanel southPanel = new JPanel();
      southPanel.add(jtf);
      southPanel.add(removePanelButton);
      southPanel.add(removeButton);

      getContentPane().add(centerPanel, BorderLayout.CENTER);
      getContentPane().add(southPanel, BorderLayout.SOUTH);

      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setBounds(100, 100, 400, 200);
      setVisible(true);
   }

/*  Pressing one of the two buttons on the bottom of the JFrame   */
/*  changes the visibility of the center panel.  This causes the  */
/*  JButton contained by the center panel to generate a           */
/*  HierarchyEvent.                                               */

   public void actionPerformed(ActionEvent event)
   {
      if ( event.getActionCommand().equals("hide"))
      {
         centerPanel.setVisible(false);
      }
      if ( event.getActionCommand().equals("show"))
      {
         centerPanel.setVisible(true);
      }
      invalidate();
      validate();
   }

/*  The HierarchyListener is implemented as an inner class.  When   */
/*  the button on the center panel fires a HierarchyEvent, it is    */
/*  sent to the hierarchyChanged() method.  This method determines  */
/*  if the event was due to a change in the visibility of some      */
/*  part of the component hierarchy.  The JTextField is updated to  */
/*  indicate if the JButton has become visible or invisible because */
/*  some part of its component hierarchy (the center panel) has     */
/*  become visible or invisible.                                    */

   class HierListener implements HierarchyListener
   {
      public void hierarchyChanged(HierarchyEvent event)
      {
         if ( event.getChangeFlags() == HierarchyEvent.SHOWING_CHANGED )
         {
            if ( event.getChanged().isVisible() )
            {
               jtf.setText("Button is visible");
            }
            else
            {
               jtf.setText("Button is not visible");
            }
         }
      }
   }

   public static void main(String args[])
   {
      HierListenerDemo demo = new HierListenerDemo();
   }
}