JFrame因某种原因移至后台。

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英文:

JFrame moves to the background for some reason

问题

昨天我问了一个关于这个主题的非常模糊的问题,链接在这里,现在我已经找到了问题并创建了一个可以展示这种行为的MCVE。

情景如下:

当后台进行某些操作时,前台提供一个模态“等待”对话框,同时将JFrame设置为禁用,以确保安全。后台任务完成后,再次启用Frame并且关闭对话框。

问题是,在启用JFrame并且关闭模态对话框后,JFrame突然移到后台。所谓的“后台”是指它在JFrame之前具有焦点的窗口的后面。为什么会发生这种情况呢?

以下代码可以复现这个问题:

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);
}

有人知道为什么会出现这种情况,以及如何防止这种情况发生吗?

英文:

After I asked a very vague question about this topic yesterday here (which I voted to close now), I was able to pinpoint the problem and create a MCVE which shows this behavior.

The scenario looks like this:

While some operation is ongoing in the background, a Modal "Wait" Dialog is provided in the foreground, also the JFrame is being set to be disabled, just to be sure. After the background task is finished, the Frame is enabled again and the dialog disposed.

The issue is, that after the JFrame is being enabled and a modal dialog is disposed, the JFrame suddenly moves to the background. With "background" meaning, it is moving behind the window that had focus before the JFrame. Why does this happen?

This code should replicate the issue:

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);
}

Does anyone know why this happens and how this could be prevented?

答案1

得分: 2

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

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;

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 {

        private String typeId;

        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) {
            if (v) {
                requestFocus();
            }
            super.setVisible(v);
        }

        @Override
        public final void focusLost(FocusEvent fe) {
            if (isVisible()) {
                requestFocus();
            }
        }

        @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
        }
    }
}
英文:

The problem is the methods frame.setEnabled(). I don't know why, but it hides the frame. My suggestion is to remove it and use the modality concept: dialog.setModal(true) (it also makes the parent frame unavailable when the dialog is shown. To make the frame unavailable, you can place a glasspane over it. Here is the code:

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
}
}
}

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  • 本文由 发表于 2020年8月21日 15:12:42
  • 转载请务必保留本文链接:https://go.coder-hub.com/63518148.html
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