在Swing中为对话框设置最初关注的组件的正确方法是什么？

Question

I have a bug lurking where the focus is sporadically not ending up on the text field I want it on after popping up a JOptionPane containing the text field.

I eventually boiled it down to a reasonable example:

import javax.swing.BorderFactory;
import javax.swing.JDialog;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import java.awt.BorderLayout;
import java.awt.Component;

public class FocusIssueTest {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                // The real thing has many more components in there,
                // but I removed them for the demo.
                MyInputPane myInputPane = new MyInputPane();
                myInputPane.showDialog(null);
            }
        });
    }

    public static class MyInputPane extends JPanel {
        private final JTextField textField;

        protected MyInputPane() {
            textField = new JTextField();
            textField.selectAll();
            textField.setColumns(30);

            setLayout(new BorderLayout());
            add(textField, BorderLayout.CENTER);
        }

        public boolean showDialog(Component parentComponent) {

            final JOptionPane optionPane = new JOptionPane(
                this, JOptionPane.PLAIN_MESSAGE,
                JOptionPane.OK_CANCEL_OPTION);

            JDialog dialog = optionPane.createDialog(
                parentComponent, "Select a Thing");

            /* Attempted solution #1 - wait until the window is active
            dialog.addWindowListener(new WindowAdapter() {
                @Override
                public void windowActivated(WindowEvent event) {
                    textField.requestFocusInWindow();
                }
            });
            */

            /* Attempted solution #2 - camickr's RequestFocusListener
            textField.addAncestorListener(new AncestorListener() {
                @Override
                public void ancestorAdded(AncestorEvent event) {
                    JComponent component = event.getComponent();
                    component.requestFocusInWindow();
                    component.removeAncestorListener(this);
                }

                @Override
                public void ancestorRemoved(AncestorEvent event) {

                }

                @Override
                public void ancestorMoved(AncestorEvent event) {

                }
            });
            */

            /* Attempted solution #3 - HierarchyListener
            textField.addHierarchyListener(new HierarchyListener() {
                @Override
                public void hierarchyChanged(HierarchyEvent event) {
                    Component component = event.getComponent();
                    if ((HierarchyEvent.SHOWING_CHANGED &
                         event.getChangeFlags()) != 0 &&
                            component.isShowing()) {
                        component.requestFocusInWindow();
                        component.removeHierarchyListener(this);
                    }
                }
            });
            */

            // Attempted solution #4 - appears to work but can't be
            // right, because eww.
            SwingUtilities.invokeLater(new Runnable() {
                @Override
                public void run() {
                    SwingUtilities.invokeLater(new Runnable() {
                        @Override
                        public void run() {
                            SwingUtilities.invokeLater(new Runnable() {
                                @Override
                                public void run() {
                                    textField.requestFocusInWindow();
                                }
                            });
                        }
                    });
                }
            });

            dialog.setVisible(true);
            Object selectedValue = optionPane.getValue();
            return selectedValue instanceof Integer &&
                   (int) selectedValue == 0;
        }
    }
}

Attempted solutions #1 through #3 all fail to put the focus in the text field. Attempted solution #4 works but having to use three levels of nested SwingUtilities.invokeLater calls can't possibly be the proper way to do this.

So what is the proper way?

I notice that JOptionPane.showInputDialog ' text field does receive focus, so clearly there is a way to do it.

Answer 1

I don't know the canonical solution, but you could try just one call to queue on the event thread within your window listener. For eg,

     dialog.addWindowListener(new WindowAdapter() {
        @Override
        public void windowActivated(WindowEvent event) {
           SwingUtilities.invokeLater(new Runnable() {
              public void run() {
                 textField.requestFocusInWindow();
              }
           });
        }
     });

Other possible "kludges" include using a short single-run Swing timer.

Answer 2

Have you considered subclassing / initializing a JDialog directly instead of using JOptionPane ?

The reason why java does not have a "setFocusInWindow" is because on some platforms it is not possible to directly "set" the focus (as much as request it. )

To me it seems like the call to "setVisible()" is putting a event on the EDT, to make the window visible, which in turn is changing the focus away from your text field.