Java Tutorial/Swing Event/ContainerListener

ContainerListener and ContainerEvent

   <source lang="java">

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/*

* ContainerEventDemo.java requires no other files.
*/

import java.awt.Dimension; import java.awt.GridBagConstraints; import java.awt.GridBagLayout; import java.awt.GridLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.ContainerEvent; import java.awt.event.ContainerListener; import java.util.Vector; import javax.swing.BorderFactory; import javax.swing.JButton; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; public class ContainerEventDemo extends JPanel implements ContainerListener,

   ActionListener {
 JTextArea display;
 JPanel buttonPanel;
 JButton addButton, removeButton, clearButton;
 Vector<JButton> buttonList;
 static final String ADD = "add";
 static final String REMOVE = "remove";
 static final String CLEAR = "clear";
 static final String newline = "\n";
 public ContainerEventDemo() {
   super(new GridBagLayout());
   GridBagLayout gridbag = (GridBagLayout) getLayout();
   GridBagConstraints c = new GridBagConstraints();
   // Initialize an empty list of buttons.
   buttonList = new Vector<JButton>(10, 10);
   // Create all the components.
   addButton = new JButton("Add a button");
   addButton.setActionCommand(ADD);
   addButton.addActionListener(this);
   removeButton = new JButton("Remove a button");
   removeButton.setActionCommand(REMOVE);
   removeButton.addActionListener(this);
   buttonPanel = new JPanel(new GridLayout(1, 1));
   buttonPanel.setPreferredSize(new Dimension(200, 75));
   buttonPanel.addContainerListener(this);
   display = new JTextArea();
   display.setEditable(false);
   JScrollPane scrollPane = new JScrollPane(display);
   scrollPane.setPreferredSize(new Dimension(200, 75));
   clearButton = new JButton("Clear text area");
   clearButton.setActionCommand(CLEAR);
   clearButton.addActionListener(this);
   c.fill = GridBagConstraints.BOTH; // Fill entire cell.
   c.weighty = 1.0; // Button area and message area have equal height.
   c.gridwidth = GridBagConstraints.REMAINDER; // end of row
   gridbag.setConstraints(scrollPane, c);
   add(scrollPane);
   c.weighty = 0.0;
   gridbag.setConstraints(clearButton, c);
   add(clearButton);
   c.weightx = 1.0; // Add/remove buttons have equal width.
   c.gridwidth = 1; // NOT end of row
   gridbag.setConstraints(addButton, c);
   add(addButton);
   c.gridwidth = GridBagConstraints.REMAINDER; // end of row
   gridbag.setConstraints(removeButton, c);
   add(removeButton);
   c.weighty = 1.0; // Button area and message area have equal height.
   gridbag.setConstraints(buttonPanel, c);
   add(buttonPanel);
   setPreferredSize(new Dimension(400, 400));
   setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
 }
 public void componentAdded(ContainerEvent e) {
   displayMessage(" added to ", e);
 }
 public void componentRemoved(ContainerEvent e) {
   displayMessage(" removed from ", e);
 }
 void displayMessage(String action, ContainerEvent e) {
   display.append(((JButton) e.getChild()).getText() + " was" + action
       + e.getContainer().getClass().getName() + newline);
   display.setCaretPosition(display.getDocument().getLength());
 }
 /*
  * This could have been implemented as two or three classes or objects, for
  * clarity.
  */
 public void actionPerformed(ActionEvent e) {
   String command = e.getActionCommand();
   if (ADD.equals(command)) {
     JButton newButton = new JButton("JButton #" + (buttonList.size() + 1));
     buttonList.addElement(newButton);
     buttonPanel.add(newButton);
     buttonPanel.revalidate(); // Make the button show up.
   } else if (REMOVE.equals(command)) {
     int lastIndex = buttonList.size() - 1;
     try {
       JButton nixedButton = buttonList.elementAt(lastIndex);
       buttonPanel.remove(nixedButton);
       buttonList.removeElementAt(lastIndex);
       buttonPanel.revalidate(); // Make the button disappear.
       buttonPanel.repaint(); // Make the button disappear.
     } catch (ArrayIndexOutOfBoundsException exc) {
     }
   } else if (CLEAR.equals(command)) {
     display.setText("");
   }
 }
 /**
  * Create the GUI and show it. For thread safety, this method should be
  * invoked from the event-dispatching thread.
  */
 private static void createAndShowGUI() {
   // Create and set up the window.
   JFrame frame = new JFrame("ContainerEventDemo");
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   // Create and set up the content pane.
   JComponent newContentPane = new ContainerEventDemo();
   newContentPane.setOpaque(true); // content panes must be opaque
   frame.setContentPane(newContentPane);
   // Display the window.
   frame.pack();
   frame.setVisible(true);
 }
 public static void main(String[] args) {
   // Schedule a job for the event-dispatching thread:
   // creating and showing this application"s GUI.
   javax.swing.SwingUtilities.invokeLater(new Runnable() {
     public void run() {
       createAndShowGUI();
     }
   });
 }

}</source>

Determining When a Component Is Added or Removed from a Container

   <source lang="java">

import java.awt.ruponent; import java.awt.event.ContainerAdapter; import java.awt.event.ContainerEvent; import java.awt.event.ContainerListener; import javax.swing.JFrame; public class Main {

 public static void main() {
   ContainerListener listener = new ContainerAdapter() {
     public void componentAdded(ContainerEvent evt) {
       
       Component c = evt.getChild();
     }
     public void componentRemoved(ContainerEvent evt) {
       
       Component c = evt.getChild();
     }
   };
   JFrame frame = new JFrame();
   frame.addContainerListener(listener);
 }

}</source>

How to Write a Container Listener

Container events are fired after a component is added to or removed from the container.

   <source lang="java">

import java.awt.event.ContainerEvent; import java.awt.event.ContainerListener; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JPanel; public class UsingContainerListener {

 public static void main(String[] a) {
   JFrame frame = new JFrame();
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   JPanel buttonPanel = new JPanel();
   buttonPanel.addContainerListener(new ContainerListener() {
     public void componentAdded(ContainerEvent e) {
       displayMessage(" added to ", e);
     }
     public void componentRemoved(ContainerEvent e) {
       displayMessage(" removed from ", e);
     }
     void displayMessage(String action, ContainerEvent e) {
       System.out.println(((JButton) e.getChild()).getText() + " was" + action
           + e.getContainer().getClass().getName());
     }
   });
   buttonPanel.add(new JButton("A"));
   frame.add(buttonPanel);
   frame.setSize(300, 200);
   frame.setVisible(true);
 }

}</source>

Using ComponentListener to catch the JFrame Maximization event

   <source lang="java">

import java.awt.Dimension; import java.awt.Frame; import java.awt.event.ruponentEvent; import java.awt.event.ruponentListener; import javax.swing.JFrame; public class Main extends JFrame implements ComponentListener {

 public Main() {
   addComponentListener(this);
 }
 public void componentHidden(ComponentEvent e) {
   System.out.println("componentHidden");
 }
 public void componentMoved(ComponentEvent e) {
   System.out.println("componentMoved");
 }
 public void componentResized(ComponentEvent e) {
   System.out.println("componentResized");
   if (getState() == Frame.ICONIFIED) {
     System.out.println("RESIZED TO ICONIFIED");
   } else if (getState() == Frame.NORMAL) {
     System.out.println("RESIZED TO NORMAL");
   } else {
     System.out.println("RESIZED TO MAXIMIZED");
   }
 }
 public void componentShown(ComponentEvent e) {
 }
 public static void main(String[] arg) {
   Main m = new Main();
   m.setVisible(true);
   m.setSize(new Dimension(300, 100));
   m.setLocation(50, 50);
 }

}</source>