Java 图标返回默认位置

Question

我已经编写了一个 GUI 应用程序，如果我将 JLabel 拖放到空白区域，它会保留在我放置的位置。但是，如果我将其放到另一个 JLabel 上，JLabel 看起来就像布局管理器已将它们移回默认位置，即使我为所有 JLabel 设置了位置。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Vector;
public class DragnDrop {
    static JFrame window=new JFrame("Drag n Drop");
    static JPanel content=new JPanel();
    static JMenu file=new JMenu("File");
    static JMenuItem clear=new JMenuItem("New");
    static JMenuItem quit=new JMenuItem("Quit");
    static JMenu edit=new JMenu("Edit");
    static JMenuItem addm=new JMenuItem("Add mole");
    static JMenuItem addh=new JMenuItem("Add hole");
    static ImageIcon hole=new ImageIcon("hole.png");
    static ImageIcon mole=new ImageIcon("mole.png");
    static JMenuBar menubar=new JMenuBar();
    static Vector<JLabel> draggables=new Vector<JLabel>();
    static Vector<Point> dragpoints=new Vector<Point>();
    static Vector<Boolean> morh=new Vector<Boolean>(); //true if mole
    static Vector<Integer> hcounts=new Vector<Integer>();
    static Vector<Integer> mcounts=new Vector<Integer>();
    public static class DragHandler extends MouseAdapter{
        int xDisp;
        int yDisp;
        int curr;
        public void mousePressed(MouseEvent e){
            JLabel tmp=(JLabel) e.getComponent();
            curr=(draggables.indexOf(tmp));
            xDisp = dragpoints.elementAt(curr).x - tmp.getLocation().x;
            yDisp = dragpoints.elementAt(curr).y - tmp.getLocation().y+63;
        }
        public void mouseReleased(MouseEvent e){
            JLabel tmp=(JLabel) e.getComponent();
            JLabel tmp2 = null;
            int toRemove=0;
            int replacement=0;
            boolean remove=false;
            toRemove=draggables.indexOf(tmp);
            for(int a=0;a<draggables.size();a++){
                if(tmp.getLocation().x>=dragpoints.elementAt(a).x&&tmp.getLocation().x<=dragpoints.elementAt(a).x+draggables.elementAt(a).getWidth()){
                    if(tmp.getLocation().y>=dragpoints.elementAt(a).y&&tmp.getLocation().y<=dragpoints.elementAt(a).y+draggables.elementAt(a).getHeight()){
                        if(draggables.elementAt(a)!=tmp&&morh.elementAt(toRemove)==true){
                            Integer temp=mcounts.elementAt(a);
                            temp=Integer.valueOf(temp.intValue()+1);
                            mcounts.setElementAt(temp,a);
                            remove=true;
                            replacement=a;
                            tmp2=(JLabel) draggables.elementAt(a);
                            break;
                        }
                        else if(draggables.elementAt(a)!=tmp){
                            Integer temp=hcounts.elementAt(a);
                            temp=Integer.valueOf(temp.intValue()+1);
                            hcounts.setElementAt(temp,a);
                            remove=true;
                            replacement=a;
                            tmp2=(JLabel) draggables.elementAt(a);
                            break;
                        }
                    }
                }
            }
            if(remove==true){
                if(hcounts.elementAt(replacement).intValue()!=0){
                    tmp2.setText(hcounts.elementAt(replacement)+"H");
                }
                if(mcounts.elementAt(replacement).intValue()!=0){
                    if(tmp2.getText()==null){
                        tmp2.setText(mcounts.elementAt(replacement)+"M");
                    }
                    else{
                        tmp2.setText(tmp2.getText()+"  "+mcounts.elementAt(replacement)+"M");
                    }
                }
                draggables.removeElementAt(toRemove);
                dragpoints.removeElementAt(toRemove);
                morh.removeElementAt(toRemove);
                mcounts.removeElementAt(toRemove);
                hcounts.removeElementAt(toRemove);
                tmp.setVisible(false);
            }
            else{
                dragpoints.setElementAt(tmp.getLocation(), curr);
            }
            content.validate();
            for(int a=0;a<draggables.size();a++){
                draggables.elementAt(a).setLocation(dragpoints.elementAt(a));
                System.out.println(draggables.elementAt(a).getLocation().x+" "+draggables.elementAt(a).getLocation().y); //debugging purposes
            }
        }
        public void mouseDragged(MouseEvent e){
            JLabel tmp = (JLabel) e.getComponent();
            PointerInfo tmppi=MouseInfo.getPointerInfo();
            Point pt=tmppi.getLocation();
            tmp.setLocation(pt.x-xDisp,pt.y-yDisp);
        }
        public void mouseMoved(MouseEvent e){
        }
    }
    public static class AddMHandler implements ActionListener{
        public void actionPerformed(ActionEvent e) {
            JLabel tmp=new JLabel(mole);
            DragHandler drag=new DragHandler();
            tmp.setLocation(0,0);
            tmp.addMouseListener(drag);
            tmp.addMouseMotionListener(drag);
            tmp.setVerticalTextPosition(SwingConstants.BOTTOM);
            tmp.setHorizontalTextPosition(SwingConstants.CENTER);
            content.add(tmp, 0);
            content.validate();
            for(int a=0;a<draggables.size();a++){
                draggables.elementAt(a).setLocation(dragpoints.elementAt(a));
            }
            draggables.add(tmp);
            dragpoints.add(new Point(0,0));
            draggables.elementAt(draggables.size()-1).setLocation(dragpoints.elementAt(draggables.size()-1));
            morh.add(new Boolean(true));
            mcounts.add(new Integer(1));
            hcounts.add(new Integer(0));
        }
    }
    public static class AddHHandler implements ActionListener{
        public void actionPerformed(ActionEvent e) {
            JLabel tmp=new JLabel(hole);
            DragHandler drag=new DragHandler();
            tmp.setLocation(0,0);
            tmp.addMouseListener(drag);
            tmp.addMouseMotionListener(drag);
            tmp.setVerticalTextPosition(SwingConstants.BOTTOM);
            tmp.setHorizontalTextPosition(SwingConstants.CENTER);
            content.add(tmp, 0);
            content.validate();
            for(int a=0;a<draggables.size();a++){
                draggables.elementAt(a).setLocation(dragpoints.elementAt(a));
            }
            draggables.add(tmp);
            dragpoints.add(new Point(0,0));
            draggables.elementAt(draggables.size()-1).setLocation(dragpoints.elementAt(draggables.size()-1));
            morh.add(new Boolean(false));
            hcounts.add(new Integer(1));
            mcounts.add(new Integer(0));
        }
    }
    public static class ClearHandler implements ActionListener{
        public void actionPerformed(ActionEvent e){
            content.removeAll();
            content.validate();
        }
    }
    public static class QuitHandler implements ActionListener{
        public void actionPerformed(ActionEvent e){
            System.exit(0);
        }
    }
    public static void main(String[] args) {
        clear.addActionListener(new ClearHandler());
        file.add(clear);
        quit.addActionListener(new QuitHandler());
        quit.setMnemonic(KeyEvent.VK_Q);
        quit.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Q, ActionEvent.META_MASK));
        file.add(quit);
        addm.addActionListener(new AddMHandler());
        addm.setMnemonic(KeyEvent.VK_M);
        addm.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_M, ActionEvent.ALT_MASK));
        edit.add(addm);
        addh.addActionListener(new AddHHandler());
        addh.setMnemonic(KeyEvent.VK_H);
        addh.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_H, ActionEvent.ALT_MASK));
        edit.add(addh);
        menubar.add(file);
        menubar.add(edit);
        window.setJMenuBar(menubar);
        window.setSize(500, 500);
        window.setLocation(0, 0);
        window.setContentPane(content);
        window.setVisible(true);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

Answer 1

我真的不知道你想用你的代码做什么。例如，我不明白为什么你有两个添加处理程序。代码看起来非常相似。

However, if I drop it onto another JLabel, the JLabels appear as if the layout manager has moved them back to the default position

通常，当您在面板周围拖动组件时，您需要使用空布局，以便组件将保留在您拖动的位置。

在您的情况下，您似乎使用的是 JPanel，它使用 FlowLayout 作为默认布局管理器，因此当您重新验证面板时，布局管理器会重置组件位置。

对于空布局，您需要使用:

panel.setLayout(null);

对于简单的拖动逻辑，您可以使用以下内容:

public class DragListener extends MouseInputAdapter
{
    Point location;
    MouseEvent pressed;

    public void mousePressed(MouseEvent me)
    {
        pressed = me;
    }

    public void mouseDragged(MouseEvent me)
    {
        Component component = me.getComponent();
        location = component.getLocation(location);
        int x = location.x - pressed.getX() + me.getX();
        int y = location.y - pressed.getY() + me.getY();
        component.setLocation(x, y);
     }
}

您只需使用以下方法将监听器添加到组件中:

DragListener drag = new DragListener();
component.addMouseListener( drag );
component.addMouseMotionListener( drag );