Sending messages between two JPanel objects

Question

I have a Java JFrame containing a JPanel. Inside this JPanel there are two separate JPanel. When the user clicks a button in the first JPanel, the message must be sent to another JPanel, notifying him which button was clicked. What is the easiest way to send messages between such objects?

Answer 1

For mKorbel (and the original poster):
What I recommend is a weaker connection, that one JPanel does not know the other JPanel and that all connections are made through some kind of control. For example, to borrow part of your code:

CopyTextNorthPanel2.java

import java.awt.*; import javax.swing.*; public class CopyTextNorthPanel2 extends JPanel { private static final long serialVersionUID = 1L; public JTextField northField; public CopyTextNorthPanel2() { northField = new JTextField("Welcome World"); northField.setFont(new Font("Serif", Font.BOLD, 20)); northField.setPreferredSize(new Dimension(300, 25)); add(northField); } public String getNorthFieldText() { return northField.getText(); } } 

CopyTextSouthPanel2.java

 import java.awt.event.*; import javax.swing.*; public class CopyTextSouthPanel2 extends JPanel { private static final long serialVersionUID = 1L; private JTextField firstText = new JTextField("Desired TextField"); private JButton copyButton = new JButton("Copy text from JTextFields"); private CopyTextControl2 control; public CopyTextSouthPanel2() { copyButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { if (control != null) { control.copyAction(); } } }); add(firstText); add(copyButton); } public void setControl(CopyTextControl2 control) { this.control = control; } public void setFirstText(String text) { firstText.setText(text); } } 

CopyTextControl2.java

 public class CopyTextControl2 { private CopyTextNorthPanel2 northPanel; private CopyTextSouthPanel2 southPanel; public void copyAction() { if (northPanel != null && southPanel != null) { southPanel.setFirstText(northPanel.getNorthFieldText()); } } public void setNorthPanel(CopyTextNorthPanel2 northPanel) { this.northPanel = northPanel; } public void setSouthPanel(CopyTextSouthPanel2 southPanel) { this.southPanel = southPanel; } } 

CopyText2.java

 import java.awt.*; import javax.swing.*; public class CopyText2 { private static void createAndShowUI() { CopyTextNorthPanel2 northPanel = new CopyTextNorthPanel2(); CopyTextSouthPanel2 southPanel = new CopyTextSouthPanel2(); CopyTextControl2 control = new CopyTextControl2(); southPanel.setControl(control); control.setNorthPanel(northPanel); control.setSouthPanel(southPanel); JPanel mainPanel = new JPanel(new BorderLayout()); mainPanel.add(northPanel, BorderLayout.NORTH); mainPanel.add(Box.createRigidArea(new Dimension(100, 100)), BorderLayout.CENTER); mainPanel.add(southPanel, BorderLayout.SOUTH); JFrame frame = new JFrame("Copy Text"); frame.getContentPane().add(mainPanel); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } public static void main(String[] args) { java.awt.EventQueue.invokeLater(new Runnable() { public void run() { createAndShowUI(); } }); } } 

Answer 2

You can create your own event and connect one or more listeners to it.

The correct way to implement this is to fire the ActionListener Button, and then your two panels will be listeners for this event.

Answer 3

at the top of your class

 public MyClass implements ActionListener { ... myButton.addActionListener(this); ... public void actionPerformed(ActionEvent e) { //for example if you have more than one events that you need to handle if(e.getSource().equals(myButton) { //update your do some work on you jpanels } } 

But actually, I think it's time to think about design patterns. What you are describing is an ideal candidate for observer and possibly a command pattern

Answer 4

for example, using the betweens Classes constructor, or (for a debugging task) extract the value from the desired JComponent (s) using getParent()

 import java.awt.*; import javax.swing.*; public class CopyTextFrame extends JFrame { private static final long serialVersionUID = 1L; private CopyTextNorthPanel northPanel; private CopyTextCenterPanel centerPanel; private CopyTextSouthPanel southPanel; public void makeUI() { northPanel = new CopyTextNorthPanel(); centerPanel = new CopyTextCenterPanel(); southPanel = new CopyTextSouthPanel(); northPanel.setName("northPanel"); centerPanel.setName("centerPanel"); southPanel.setName("southPanel"); centerPanel = new CopyTextCenterPanel(); centerPanel.setPreferredSize(new Dimension(300, 40)); southPanel = new CopyTextSouthPanel(); southPanel.setSourceTextField(northPanel.desText); northPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK, 1)); centerPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK, 1)); southPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK, 1)); setLayout(new BorderLayout(5, 5)); setDefaultCloseOperation(EXIT_ON_CLOSE); add(northPanel, BorderLayout.NORTH); add(centerPanel, BorderLayout.CENTER); add(southPanel, BorderLayout.SOUTH); pack(); setVisible(true); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { new CopyTextFrame().makeUI(); } }); } } 

+

 import javax.swing.*; public class CopyTextCenterPanel extends JPanel { private static final long serialVersionUID = 1L; public CopyTextCenterPanel() { } } 

+

 import java.awt.*; import javax.swing.*; public class CopyTextNorthPanel extends JPanel { private static final long serialVersionUID = 1L; public JTextField desText; public CopyTextNorthPanel() { desText = new JTextField("Welcome World"); desText.setFont(new Font("Serif", Font.BOLD, 20)); desText.setPreferredSize(new Dimension(300, 25)); desText.setBorder(BorderFactory.createLineBorder(Color.BLACK, 1)); desText.addComponentListener(null); desText.setName("desText"); add(desText); } public JTextField getDesText() { return desText; } } 

+

 import java.awt.*; import java.awt.event.ActionEvent; import javax.swing.*; public class CopyTextSouthPanel extends JPanel { private static final long serialVersionUID = 1L; private JTextField firstText; private JButton copyButton; private JTextField sourceTextField; private String lds = ""; public CopyTextSouthPanel() { firstText = new JTextField("Desired TextField"); firstText.setMinimumSize(new Dimension(300, 25)); firstText.setPreferredSize(new Dimension(300, 25)); firstText.setMaximumSize(new Dimension(300, 25)); copyButton = new JButton("Copy text from JTextFields"); copyButton.setMinimumSize(new Dimension(200, 25)); copyButton.setPreferredSize(new Dimension(200, 25)); copyButton.setMaximumSize(new Dimension(200, 25)); copyButton.addActionListener(new java.awt.event.ActionListener() { @Override public void actionPerformed(java.awt.event.ActionEvent evt) { copyButtonActionPerformed(evt); } private void copyButtonActionPerformed(ActionEvent evt) { System.out.print("Button pressed" + "\n"); Component[] comp = CopyTextSouthPanel.this.getParent().getComponents(); int nO = comp.length; for (int i = 0; i < comp.length; ++i) { if (comp[i] instanceof JPanel) { String name = ((JPanel) comp[i]).getName(); if (name.equals("northPanel")) { JPanel panel = (JPanel) comp[i]; Component[] comp1 = panel.getComponents(); int nO1 = comp1.length; for (int ii = 0; ii < comp1.length; ++ii) { if (comp1[ii] instanceof JTextField) { String name1 = ((JTextField) comp1[ii]).getName(); if (!(name1 == null)) { if (name1.equals("desText")) { JTextField text = (JTextField) comp1[ii]; String str = text.getText(); firstText.setText(str); System.out.print("set value -> " + str + "\n"); break; } } } } break; } } } lds = sourceTextField.getText(); if (lds != null || (!(lds.isEmpty()))) { firstText.setText(" Msg -> " + lds); } } }); add(firstText, BorderLayout.EAST); add(copyButton, BorderLayout.WEST); } public void setSourceTextField(JTextField source) { this.sourceTextField = source; } }