Develop Reference

JDialog not centered over parent JFrame

I am trying to get my JDialog to popup in the center of my JFrame on a button click. I have JOptionPanel that popup correctly over the parent JFrame, but the JDialog is popping up relative to the JFrame but not in the center.
The buttons are actually JMenuItem in my code, but I wrote them here as JButton to make things easier and straight forward.
Here's my code:
call from my Parent JFrame:
JButton about = new JButton("About");
about.addActionListener(new ActionListener() { //this one IS NOT in the center of MyJFrame
public void actionPerformed(ActionEvent e) {
new AboutDialog(MyJFrame.this);
}
});
JButton exit = new JButton("Exit");
exit.addActionListener(new ActionListener() { //this one IS in the center of MyJFrame
public void actionPerformed(ActionEvent e) {
if(JOptionPane.showConfirmDialog(MyJFrame.this, "Are you sure you want to exit ?","",JOptionPane.YES_NO_OPTION) == 0)
System.exit(0);
}
});
AboutDialog Class
public class AboutDialog extends JDialog{
public AboutDialog(JFrame parent) {
setLocationRelativeTo(parent);
setLayout(new BorderLayout());
...
Thank you

setLocationRelativeTo(parent);
The above code needs to be executed AFTER you have added all the components to the dialog and packed the dialog and before you make the dialog visible.
In your current code the size of the dialog is (0, 0) so it can't be centered properly.

Enable only mouse event over a jbutton - Disable keyboard event for jbutton

I have a problem.
I created a game. When I open it I must press ENTER to start the game (just enter).
Now I upgraded the game with one button named "EXIT GAME". I don't know why my enter key doesn't work anymore because of this button. If i remove it then Ican press enter again and play the game.
I must set only click pressed event to that button or something like this? Please help me.
public class LeftPanel extends JPanel implements ActionListener {
JButton ExitGame;
public LeftPanel(Tetris tetris) {
this.tetris = tetris;
setPreferredSize(new Dimension(400, 480));
setBackground(Color.getHSBColor(17f, 0.87f, 0.52f));
add(new JButton("Exit Game"));
{
ExitGame.addActionListener(this);
}
}
public void actionPerformed(ActionEvent e) {
System.exit(0);
}
}

Problem 1 - The JButton is the only focusable component within your UI. Therefore, when you start you program, it gains default focucs. While it has default focus. It will consume the Enter key strokes.
Problem 2 - JPanel is not focusable, meaning it can never receive key board focus. From your description, I would assume you are using a KeyListener, which leads to
Problem 3 - Using KeyListener...KeyListener will only respond to key events when the component it is registered to is focusable and has focus. You can over come this by using Key Bindings.
...Solutions...
Use JLabel instead of JButton. This will require you to register a MouseListener to the label in order to recieve notification of the mouse clicks, but it won't respond to key events...
Better still, add a "Start" button as well...

You can try:
public class LeftPanel extends JPanel implements ActionListener {
public LeftPanel(Tetris tetris) {
this.tetris = tetris;
setPreferredSize(new Dimension(400, 480));
setBackground(Color.getHSBColor(17f, 0.87f, 0.52f));
JButton ExitGame = new JButton("Exit Game");
ExitGame.addActionListener(this);
ExitGame.setActionCommand("Exit");
add(ExitGame );
}
public void actionPerformed(ActionEvent e) {
if("Exit".equals(e.getActionCommand())
System.exit(0);
}
}

This line looks like a syntax error:
add(new JButton("Exit Game"));
{
ExitGame.addActionListener(this);
}
I think it should be something like this:
ExitGame= new JButton("Exit");
this.add(ExitGame);
ExitGame.addActionListener(this);
I haven't tested this, but I think with some tweaking you should be able to get it to do what you want it to. I hope that works!
-Frank

public void actionPerformed(ActionEvent e) {
if("Exit".equals(e.getActionCommand())
System.exit(0);
}

As ActionlListener can be triggered by both Mouse and Keyboard, but now user only want to response mouse event, so change the action listener to mouselistener. Tested and passed.
public class LeftPanel extends JPanel implements ActionListener {
JButton ExitGame;
public LeftPanel(Tetris tetris) {
this.tetris = tetris;
setPreferredSize(new Dimension(400, 480));
setBackground(Color.getHSBColor(17f, 0.87f, 0.52f));
ExitGame= new JButton("Exit Game")
add(ExitGame);
ExitGame.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e) {
System.exit(0);
}
});
}
}

Create JLabel in actionPerformed in Java

Hi I have a JButton that I want to program so that when pressed, a new JLabel is displayed on screen. I have added the JLabel to the frame and it is visible. It shows outside of actionPerformed but not inside it.
The label is declared as lbl outside the method and then it is created in the actionPerformed method
public void actionPerformed(ActionEvent e) {
JLabel lbl = new JLabel("ONE");
}
Can anybody help me to make the label appear when the button is pressed? Thanks

This is the way you do it:
public void actionPerformed(ActionEvent e) {
if (e.getSource() == buttonname){
labelname.setVisible(true);
}
}
Also, don't forget to do
buttonname.addActionListener(this);
and in your method where you layout the form add this:
yourPanel.Add(labelname)
Hope this helps!
Arno

You created the JLabel, but you did not add it to any container. That is why it is not showing. What you wrote is good, all you need is to add the label to the container it is supposed to be on.
JLabel lbl = new JLabel("ONE");
yourPanel.Add(lbl);

You have also declared it inside the actionPerformed method - this declaration is perhaps hiding the earlier one (outside the method). Can you post more code? The following code works fine for me:
public class NewLabel
{
public static void main(String[] args)
{
final JFrame frame = new JFrame();
JButton button = new JButton("Add label");
button.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
JLabel lbl = new JLabel("ONE");
frame.add(lbl);
frame.setSize(100, 100);
// or you can't see the new button without resizing manually!
}
});
frame.add(button);
frame.pack();
frame.setVisible(true);
}
}
(In some cases you may also need to tell the container/frame to re-layout, by calling revalidate() on it...)

Detect mouse click anywhere on window

I've written a JWindow that acts a bit like a fancy menu in my application, popping up when a button is pressed. However, I'd like it to disappear if the user clicks anywhere in the main window. I can of course add a mouse listener to the main window, but that doesn't add it to all the components on the window itself, and looping over all the components seems like a bit of a brute force solution (and can't be guaranteed to work if the components on the window change.)
What's the best way of going about doing something like this?

Try to use Toolkit.getDefaultToolkit().addAWTEventListener(listener, eventMask). Find eventMask that filters only mouse clicks. This AWT listener is global for whole application, so you can see all events that happen.

I'd like it to disappear if the user clicks anywhere in the main window
Add a WindowListener to the child window and then handle the windowDeactiveated() event and invoke setVisible(false) on the child window.
Working example:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class DialogDeactivated
{
public static void main(String[] args)
{
final WindowListener wl = new WindowAdapter()
{
public void windowDeactivated(WindowEvent e)
{
e.getWindow().setVisible(false);
}
};
JButton button = new JButton("Show Popup");
button.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
JButton button = (JButton)e.getSource();
JFrame frame = (JFrame) SwingUtilities.windowForComponent(button);
JDialog dialog = new JDialog(frame, false);
dialog.setUndecorated(true);
dialog.add( new JButton("Dummy Button") );
dialog.pack();
dialog.setLocationRelativeTo( frame );
dialog.setVisible( true );
dialog.addWindowListener( wl );
}
});
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(button, BorderLayout.NORTH);
frame.setSize(400, 400);
frame.setLocationRelativeTo( null );
frame.setVisible( true );
}
}

Performing action when closing JFrame

In my program I have a main JFrame that holds a button. When this button is clicked a new JFrame appears in which I can change some information. Whenever I finish editing I press a save button on the new JFrame which saves the changes and disposes the JFrame. Now when this is done, I'd like to perform an action in the main JFrame as well, but only if something changed. If I open the new JFrame and just close it again without using the save button, I don't want to do anything in the main frame.
I've tried searching the web for a solution, but just don't seem to be anything useful out there..
An example of the code I've got so far:
Main Frame...
public class MainFrame extends JFrame
{
public MainFrame()
{
super("Main Frame");
JButton details = new JButton("Add Detail");
add(details);
details.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
new DetailFrame().setVisible(true);
}
});
}
}
Detail Frame...
public class DetailFrame extends JFrame
{
public DetailFrame()
{
super("Detail Frame");
JButton save = new JButton("Save");
add(save);
save.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
// Save whatever content
dispose();
}
});
}
}
So when I click the "Save" button on the Detail Frame, I want to do something in the Main Frame, whereas when the "x" is clicked on the Detail Frame, I don't want to do anything..
Hope someone is able to help me, and sorry for my english..

You can pass a MainFrame handle to the DetailFrame constructor. Then, on clicking the Save button, the DetailFrame would call a function in MainFrame and pass the changes to it.
Another way is to create a public boolean variable in DetailFrame and set it to true when the Save button is clicked. This way MainFrame will know whether the DetailFrame was closed or Save'd.
EDIT: Some more ideas:
Use JDialog instead of JFrame. JDialog.setVisible is modal, i.e. it will block the calling function until the dialog is closed; this way you can process the results of the dialog in the same "Details" button listener.
To access the dialog after it is called, store the dialog in a separate variable. First construct the dialog, then show it, and then process the result by analyzing its variables.
Store the results of editing in other public variables of DetailFrame (or let's call it DetailDialog). This should happen only when the "Save" button is clicked. This may even allow to go without the boolean variable (depends on the types of values you are editing).
DetailDialog dlg = new DetailDialog();
dlg.setVisible(true);
if(dlg.approvedResult != null) {
// process the result...
}
EDIT: Sorry, JDialog is not modal by default. Need to call a special super constructor to make it modal.
Also, here you will have to pass the reference to MainFrame to the dialog constructor, but you still can declare it as a simple JFrame and avoid unnecessary dependencies.
To get the reference to the enclosing MainFrame from within the anonymous ActionListener, use MainFrame.this.
To be able to change the button text after it was created, you will have to store the button in a member variable.
Main Frame...
public class MainFrame extends JFrame
{
private JButton details = new JButton("Add Detail");
public MainFrame()
{
super("Main Frame");
getContentPane().add(details);
details.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
DetailDialog dlg = new DetailDialog(MainFrame.this);
dlg.setVisible(true);
if(dlg.approved){
details.setText("Edit Detail");
}
}
});
}
}
Detail Dialog... (not Frame)
public class DetailDialog extends JDialog
{
public boolean approved = false;
public DetailDialog(JFrame parent)
{
super(parent,"Detail Dialog",true); // modal dialog parented to the calling frame
JButton save = new JButton("Save");
getContentPane().add(save);
save.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
// Save whatever content
approved = true;
dispose();
}
});
}
}

Create the detail frame in the main frame, and add a windowlistener to it, using the windowadapter class. Implement the windowclosing event by checking for changes, handle those, and then dispose the detail frame. This is all done in the mainframe.
The detail frame should have do nothing on close set to prevent the detail frame being disposed before you recorded the changes.
You may wish to implement checking for changes in the detailframe as a method returning a class holding the interesting data. That way your windowlistener can be small an to the point.

Forget the 2nd JFrame. use a modal dialog instead. It will block input until dismissed. Once dismissed, the only thing to do is decide whether to update the original data. JOptionPane has some inbuilt functionality that makes that easy. If the user presses Cancel or the esc key, the showInputDialog() method will return null as the result.
import java.awt.BorderLayout;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
class EditInfo {
public static void main(String[] args) {
Runnable r = new Runnable() {
public void run() {
final JFrame f = new JFrame("Uneditable");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel p = new JPanel(new BorderLayout(10,10));
final JTextField tf = new JTextField("Hello World!", 20);
tf.setEnabled(false);
p.add(tf, BorderLayout.CENTER);
JButton edit = new JButton("Edit");
edit.addActionListener( new ActionListener(){
public void actionPerformed(ActionEvent ae) {
String result = JOptionPane.showInputDialog(
f,
"Edit text",
tf.getText());
if (result!=null) {
tf.setText(result);
}
}
} );
p.add(edit, BorderLayout.EAST);
p.setBorder(new EmptyBorder(10,10,10,10));
f.setContentPane(p);
f.pack();
f.setLocationByPlatform(true);
f.setVisible(true);
}
};
SwingUtilities.invokeLater(r);
}
}
If it is necessary to edit a number of fields all at once in the JOptionPane, use a JPanel to contain them all, and put them in a showMessageDialog() call. Check the integer based return result to determine if the user OK'd the changes.