我怎样才能无条件地让我的 swing 组件呈现在所有其他组件之上？

Question

I have a JComponent , specifically a JLabel , that I want to render above all other components in my UI. I've made it draggable viathis code , and I'd like it to render above everything else in the UI while being dragged.

I've attempted to use a JLayeredPane , but I couldn't get it to work with my UI, which is huge and complicated. Ideally there's some sort of solution that I can simply implement in the component's paint(Graphics) method.

Answer 1

solved this myself through the usage of a glass pane, this code should work in nearly every case. the only issue I've found is that the mouse/component position may not be exactly synced if the user has a taskbar position other than bottom.

thanks to https://stackoverflow.com/users/992484/madprogrammer for suggesting I use swing's glass pane to fix it.

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import java.awt.Dimension;
import java.awt.GraphicsEnvironment;
import java.awt.Rectangle;
import java.awt.Toolkit;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

public class DraggableLabel extends JLabel {
    private JComponent initialParent;

    public DraggableLabel(String text) {
        super(text);
        this.setOpaque(false);

        this.addMouseListener(new MouseListener() {
            @Override
            public void mouseClicked(MouseEvent e) {
                // no-op
            }

            @Override
            public void mousePressed(MouseEvent e) {
                // save parent for re-addition after dragging is finished
                DraggableLabel.this.initialParent = (JComponent) DraggableLabel.this.getParent();

                // configure object to be on the glass pane instead of its former pane
                DraggableLabel.this.setVisible(false);
                JPanel glassPane = (JPanel) SwingUtilities.getRootPane(DraggableLabel.this).getGlassPane();
                DraggableLabel.this.initialParent.remove(DraggableLabel.this);
                glassPane.add(DraggableLabel.this);

                // repaint former panel to display removal of element
                DraggableLabel.this.initialParent.repaint();

                // set up glass pane to actually display elements
                glassPane.setOpaque(false);
                glassPane.setVisible(true);
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                // remove from glass pane
                JPanel glassPane = (JPanel) SwingUtilities.getRootPane(DraggableLabel.this).getGlassPane();
                glassPane.remove(DraggableLabel.this);

                // add to former panel
                DraggableLabel.this.initialParent.add(DraggableLabel.this);
                DraggableLabel.this.initialParent.repaint();

                DraggableLabel.this.initialParent = null;
            }

            @Override
            public void mouseEntered(MouseEvent e) {
                // no-op
            }

            @Override
            public void mouseExited(MouseEvent e) {
                // no-op
            }

        });
        this.addMouseMotionListener(new MouseMotionListener() {
            @Override
            public void mouseDragged(MouseEvent e) {
                // get task bar height
                Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
                Rectangle windowSize = GraphicsEnvironment.getLocalGraphicsEnvironment().getMaximumWindowBounds();
                int taskBarHeight = (int) (screenSize.getHeight() - windowSize.getHeight());

                int mouseScreenX = e.getXOnScreen();
                int mouseScreenY = e.getYOnScreen();

                // calculate, offsetting y for the task bar
                // note: task bar offsetting will probably break if people have their taskbar at the top of the screen!
                // good thing I don't care!
                JFrame frame = (JFrame) SwingUtilities.getRoot(DraggableLabel.this);
                int mouseFrameX = mouseScreenX - frame.getX();
                int mouseFrameY = mouseScreenY - frame.getY() - taskBarHeight;

                // set location and ensure visibility
                DraggableLabel.this.setLocation(mouseFrameX, mouseFrameY);
                DraggableLabel.this.setVisible(true);
            }

            @Override
            public void mouseMoved(MouseEvent e) {
                // no-op
            }
        });
    }
}