Java Swing Events/Listeners
There are two ways to implement Swing Events/Listeners:
1. Have everything in 1 file and have anonymous inner classes that implement the listeners.
2. Have a main GUI class that has separate classes of JPanels that implement the listeners.
I have worked with case 1 where everything is in one file so that I can call functions within the one GUI class when an event is caught. I am having problems with approach 2 because I do not know how to call functions in the main GUI class when an event is caught in the separate JPanel classes.
Right now I have a GUI.java and a TreePanel.java, GUI.java is the main class and contains a panel TreePanel. TreePanel implements TreeSelectionListener and extends JPanel and catches an event. My question is, how do I call a function in the GUI class from TreePanel? Doing a "super" in TreePanel will give me JPanel. Doing getParent() on TreePanel's parent containers until it reaches the JFrame of GUI didn't help because my GUI is not a JFrame.
Any ideas?
[1033 byte] By [
tomkitta] at [2007-11-26 12:46:43]
> how do I call a function in the GUI class from TreePanel?
TreePanel needs a reference to GUI. So for instance when in GUI you
create a new TreePanel, you could pass "this" as an argument to
TreePanel's constructor.
GUI should implement some method that is carried out in response to
selection events. This method should be accessible from TreePanel.
Then, when a TreePanel object detects a selection event, it calls the method
in the GUI (to which it has a reference).
[Edit] I forgot to add that you really should post this sort of question in the Swing
forum. It strikes me that there are lots of ways to organise things (should
GUI be a JFrame, or contain a JFrame? Should GUI expose a method
which theTreePanel uses, or should the TreePanel provide a method
so that the GUI can make itself a listener for the selection events.) The best
knowledge - and hence the best answers - will be in the Swing forum.
This does what you are talking about (I think) but with a button rather than a
list./*
* File: listen/GUI.java
*/
package listen;
import javax.swing.JFrame;
import javax.swing.UIManager;
public class GUI {
JFrame frame;
GUI() {
frame = new JFrame("Listener test");
// Pass the ButtonPanel a reference to "this" so it
// it knows who to inform about events.
frame.add(new ButtonPanel(this));
}
public void processClick() {
System.out.println("Ding!");
}
public static void main(String[] args) {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception e) {}
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame.setDefaultLookAndFeelDecorated(true);
GUI app = new GUI();
app.frame.pack();
app.frame.setVisible(true);
}
});
}
}
// End file listen/GUI.java
/*
* File: listen/ButtonPanel.java
*/
package listen;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JPanel;
public class ButtonPanel extends JPanel implements ActionListener {
// The GUI that should be informed about events
private GUI app;
public ButtonPanel(GUI app) {
this.app = app;
JButton but = new JButton("Click me!");
but.addActionListener(this);
add(but);
}
// We catch the button clicks here
public void actionPerformed(ActionEvent e) {
// And pass it on to the GUI container/"parent"
app.processClick();
}
}
// End file listen/ButtonPanel.java
[Edit]Changed example when I read more closely and realised GUI
was not intended to be a JFrame.
