在 Swing 中为对话框设置初始焦点组件的正确方法是什么？

Question

在弹出包含文本字段的JOptionPane 后，我有一个潜伏的错误，焦点偶尔不会落在我想要的文本字段上。

我最终把它归结为一个合理的例子：

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;
        }
    }
}

尝试的解决方案 #1 到 #3 都未能将焦点放在文本字段中。尝试的解决方案 #4 可行，但必须使用三层嵌套的 SwingUtilities.invokeLater 调用不可能是正确的方法。

那么是正确的方法是什么？

我注意到 JOptionPane.showInputDialog' 文本字段确实获得焦点，所以显然有办法做到这一点。

Answer 1

我不知道规范的解决方案，但您可以尝试在窗口侦听器内的事件线程上仅调用一次队列。例如，

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

其他可能的“麻烦”包括使用短的单次运行 Swing 计时器。

Answer 2

您是否考虑过直接继承/初始化 JDialog 而不是使用 JOptionPane ？

java没有“setFocusInWindow”的原因是因为在某些平台上无法直接“设置”焦点（只要请求它。）

在我看来，对“setVisible()”的调用似乎是在 EDT 上放置一个事件，以使窗口可见，这反过来又将焦点从您的文本字段上移开。