Java Swing - JDialog default setting

Question

I found the following information on the Internet :

"When the JDialog (or JFrame, for that matter) becomes visible, focus is placed on the first custom component by default."

Consider the following code:

public class MyDialog extends JDialog{ // Dialog components: private JLabel dialogLabel1 = new JLabel("Hello"); private JLabel dialogLabel2 = new JLabel("Message"); private JButton dialogBtn = new JButton("Sample Btn text"); public MyDialog(JFrame parent, String title, ModalityType modality){ super(parent, title, modality); dialogBtn.setName("Button"); // dialogLabel1.setName("Label1"); // - setting names dialogLabel2.setName("Label2"); // setTitle(title); setModalityType(modality); setSize(300, 100); setLocation(200, 200); // adding comps to contentPane getContentPane().add(dialogLabel1, BorderLayout.PAGE_START); getContentPane().add(dialogBtn, BorderLayout.CENTER); getContentPane().add(dialogLabel2, BorderLayout.PAGE_END); pack(); } public void showDialog(){ setVisible(true); listComps(rootPane.getComponents()); setDefaultCloseOperation(DISPOSE_ON_CLOSE); } /* * Itereates through all subcomps recursively and displays some relevant info * OUTPUT FORM: ComponentName | isFocusable | hasFocus */ private void listComps(Component[] comps){ if(comps.length == 0) return; for(Component c : comps){ JComponent jC = (JComponent)c; System.out.println(jC.getName() + " | " + jC.isFocusable() +" | " + jC.hasFocus()); listComps(jC.getComponents()); } } public static void main(String[] args) { final JFrame frame = new JFrame(); frame.setPreferredSize(new Dimension(300, 400)); frame.setVisible(true); JButton btn = new JButton("Show dialog"); btn.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { MyDialog dialog = new MyDialog(frame, "Sample title", ModalityType.APPLICATION_MODAL); dialog.showDialog(); } }); frame.add(btn, BorderLayout.CENTER); frame.pack(); } } 

Output: run:

 null.glassPane | true | false null.layeredPane | true | false null.contentPane | true | false Label1 | true | false Button | true | true Label2 | true | false 

Why is the focus set to JButton? This is not the first custom component! When I removed JButton, focus was not obtained to any component. What for? By default, all songs are tuned ...

Answer 1

This is not the first custom component! When I removed JButton, focus was not obtained to any component. What for? By default, all composite objects are customizable.

To answer the question why: this is a FocusTraversalPolicy solution, in particular, accept (..) in DefaultFocusTraversalPolicy, which ultimately reverts to a dummy NullComponentPeer (which by default is not configurable since it does not actually exist :-)

From your comment, it seems that the real question might be “how to implement keyBindings if rootPane has no focal children” - if so, then the parameters

• use rootPane componentInputMap, i.e. WHEN_IN_FOCUSED_WINDOW
• enforces rootPane (perhaps this is best done only if there are no inactive children)

Answer 2

Take a look at the Javabel javadoc It says:

The display area of ​​a short text line or image, or both. The label does not respond to input events. As a result, he cannot get keyboard focus.

I think that’s why your shortcut does not receive focus.