After experimentation, it appears to me that Swing's GroupLayout tends to lose Components intended for re-use across my GUI.
But I haven't seen anything in the documentation that makes this single-use rule clear. This makes me wonder if I have made a mistake, or if I am a poor reader.
For example, I make a JPanel with a GroupLayout of a JButton("Foo"). Then I make another JPanel with a GroupLayout of the same JButton renamed "Bar".
If I switch back to the first JPanel from the second JPanel with JFrame.setContentPane, I lose the JButton in the first JPanel.
Can anyone explain why it is losing Components and further, can anyone provide a way to overcome the tendency to lose Components?
Here is a complete SSCCE demonstrating the problem:
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class GroupLayoutTest {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
deployGroupLayoutTest();
}
});
}
static JPanel firstPanel;
static JButton jbtnActionLog;
static JFrame systemFrame;
public static void deployGroupLayoutTest() {
systemFrame = new JFrame("Group Layout Test");
systemFrame.setSize(300, 300);
firstPanel = new JPanel();
JMenuBar jmbSystem = new JMenuBar();
JMenu jmuAction = new JMenu("Action");
JMenuItem jmiActionLog = new JMenuItem("Login");
jmuAction.add(jmiActionLog);
jmbSystem.add(jmuAction);
jbtnActionLog = new JButton("Login");
jbtnActionLog.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
setContentPaneToSecondPanel();
}
});
systemFrame.setJMenuBar(jmbSystem);
GroupLayout gl = new GroupLayout(firstPanel);
firstPanel.setLayout(gl);
gl.setAutoCreateContainerGaps(true);
gl.setAutoCreateGaps(true);
GroupLayout.ParallelGroup hGroup = gl.createParallelGroup(GroupLayout.Alignment.CENTER);
hGroup
.addComponent(jbtnActionLog);
gl.setHorizontalGroup(hGroup);
GroupLayout.SequentialGroup vGroup = gl.createSequentialGroup();
vGroup
.addComponent(jbtnActionLog);
gl.setVerticalGroup(vGroup);
systemFrame.getContentPane().add(firstPanel);
systemFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
systemFrame.setLocationByPlatform(true);
systemFrame.setVisible(true);
}
public static void setContentPaneToSecondPanel() {
jbtnActionLog.setText("Logout");
ActionListener[] listenerList = jbtnActionLog.getActionListeners();
jbtnActionLog.removeActionListener(listenerList[0]);
jbtnActionLog.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
systemFrame.setContentPane(firstPanel);
systemFrame.revalidate();
}
});
JPanel secondPanel = new JPanel();
GroupLayout gl = new GroupLayout(secondPanel);
secondPanel.setLayout(gl);
gl.setAutoCreateContainerGaps(true);
gl.setAutoCreateGaps(true);
GroupLayout.ParallelGroup hGroup = gl.createParallelGroup(GroupLayout.Alignment.CENTER);
hGroup
.addComponent(jbtnActionLog);
gl.setHorizontalGroup(hGroup);
GroupLayout.SequentialGroup vGroup = gl.createSequentialGroup();
vGroup
.addComponent(jbtnActionLog);
gl.setVerticalGroup(vGroup);
systemFrame.setContentPane(secondPanel);
systemFrame.revalidate();
}
}
I did not go through all of your code, but it is simply not possible to add a single Swing component to multiple parents. Each component can only be present in one location in the Swing hierarchy. So the code
JPanel firstPanel = ...;
JPanel secondPanel = ...;
JButton button = ...;
firstPanel.add( button );
secondPanel.add( button );
will result in button
only contained in one of the panels, and not in both. This has nothing to do with the GroupLayout
.
A relevant SO question contains the link to the Swing tutorial explaining this:
Each GUI component can be contained only once. If a component is already in a container and you try to add it to another container, the component will be removed from the first container and then added to the second