JFrame 出于某种原因移至后台

Question

在我昨天就这个话题提出了一个非常模糊的问题here（我现在投票结束）之后，我能够查明问题并创建一个显示这种行为的 MCVE。

场景如下：

当一些操作在后台进行时，前台提供了一个模态“等待”对话框，JFrame 也被设置为禁用，只是为了确定。后台任务完成后，再次启用Frame并释放对话框。

问题是，在启用 JFrame 并释放模态对话框后，JFrame 突然移动到后台。具有“背景”的含义，它在 JFrame 之前具有焦点的窗口后面移动。为什么会这样？

此代码应复制问题：

private static JFrame frame;
private static JDialog dialog;

public static void main(String[] args) {
    try {
        SwingUtilities.invokeAndWait(new Runnable() {

            @Override
            public void run() {
                buildFrame();
                buildDialog();
            }
        });
    } catch (InvocationTargetException | InterruptedException e) {
        e.printStackTrace();
    }
}

protected static void buildDialog() {
    dialog = new JDialog(frame);
    dialog.getContentPane().add(new JLabel("This is the dialog"));
    dialog.setLocationRelativeTo(frame);
    javax.swing.Timer t = new javax.swing.Timer(1000, new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            dialog.dispose();
            frame.setEnabled(true);
        }
    });
    t.setRepeats(false);
    t.start();
    dialog.pack();
    dialog.setVisible(true);
}

protected static void buildFrame() {
    frame = new JFrame();
    frame.setMinimumSize(new Dimension(400, 400));
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(new JLabel("This is the Frame"));
    frame.setEnabled(false);
    frame.pack();
    frame.setVisible(true);
}

有谁知道为什么会发生这种情况以及如何防止这种情况发生？

Answer 1

问题在于方法frame.setEnabled()。我不知道为什么，但它隐藏了框架。我的建议是删除它并使用模态概念：dialog.setModal(true)（它还会在显示对话框时使父框架不可用。要使框架不可用，您可以在其上放置一个玻璃窗格。这是代码：

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.awt.event.MouseAdapter;
import java.lang.reflect.InvocationTargetException;

import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

/**
 * <code>DialogFrameTest</code>.
 */
public class DialogFrameTest {
    private static JFrame frame;

    private static JDialog dialog;

    private static Component oldGlassPane;

    public static void main(String[] args) {
        try {
            SwingUtilities.invokeAndWait(new Runnable() {

                @Override
                public void run() {
                    buildFrame();
                    buildDialog();
                }
            });
        } catch (InvocationTargetException | InterruptedException e) {
            e.printStackTrace();
        }
    }

    protected static void buildDialog() {
        dialog = new JDialog(frame);
        dialog.getContentPane().add(new JTextField("This is the dialog"));
        dialog.setLocationRelativeTo(frame);
        dialog.setModal(true);
        javax.swing.Timer t = new javax.swing.Timer(1000, new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                dialog.dispose();
                frame.setGlassPane(oldGlassPane);
                oldGlassPane.setVisible(false);
            }
        });
        t.setRepeats(false);
        t.start();
        dialog.pack();
        dialog.setVisible(true);
    }

    protected static void buildFrame() {
        frame = new JFrame();
        frame.setMinimumSize(new Dimension(400, 400));
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new JTextField("This is the Frame"));
        oldGlassPane = frame.getGlassPane();
        frame.setGlassPane(new SplashGlassPane());
        frame.getGlassPane().setVisible(true);
        frame.pack();
        frame.setVisible(true);
    }

    private static class SplashGlassPane extends JPanel implements FocusListener {

        /** Holds the id of this panel. The creator of this object can submit this id to determine whether it's the owner of this object. */
        private String typeId;

        /**
         * Creates new GlassPane.
         */
        public SplashGlassPane() {
            addMouseListener(new MouseAdapter() {});
            addMouseMotionListener(new MouseAdapter() {});
            addFocusListener(this);
            setOpaque(false);
            setFocusable(true);
            setBackground(new Color(0, 0, 0, 100));
        }

        @Override
        public final void setVisible(boolean v) {
            // Make sure we grab the focus so that key events don't go astray.
            if (v) {
                requestFocus();
            }
            super.setVisible(v);
        }

        // Once we have focus, keep it if we're visible
        @Override
        public final void focusLost(FocusEvent fe) {
            if (isVisible()) {
                requestFocus();
            }
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public final void paint(Graphics g) {
            final Color old = g.getColor();
            g.setColor(getBackground());
            g.fillRect(0, 0, getSize().width, getSize().height);
            g.setColor(old);
            super.paint(g);
        }

        @Override
        public void focusGained(FocusEvent fe) {
            // nothing to do
        }
    }

}