如何将图像从一个面板拖到另一个面板

问题描述

我创建了一个框架，然后在其中创建了面板.我已将图像放在一个面板中，现在我需要将该图像拖到另一个面板中.我怎么能那样做.请作为初学者一步一步解释.

I had created a frame and then panels in it. I had placed an image in one panel, now I need to drag that image to another panel. How could I do that. Please explain step by step as am a beginner.

推荐答案

使用纯java、DragGestureListener、DropTargetAdapter和TransferHandler的快速示例一个面板上的图像到另一个面板的 DnD 支持:

Quick example using pure java, DragGestureListener, DropTargetAdapter and TransferHandler for DnD support of images on one panel to another:

在单击和拖动任何形状之前:

Before any shape is clicked and dragged:

选择绿色形状并拖动到上面的空白面板后:

after green shape is selected and dragged onto empty panel above:

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Point;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DragGestureEvent;
import java.awt.dnd.DragGestureListener;
import java.awt.dnd.DragSource;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetAdapter;
import java.awt.dnd.DropTargetDropEvent;
import java.io.IOException;
import java.net.URL;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.TransferHandler;
import javax.swing.TransferHandler.TransferSupport;
import javax.swing.border.TitledBorder;

public class Test {

    public static void main(String[] args) {
        createAndShowJFrame();
    }

    public static void createAndShowJFrame() {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {

                JFrame frame = createJFrame();
                frame.setVisible(true);

            }
        });
    }

    private static JFrame createJFrame() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        frame.setTitle("Test");

        JPanel panel = createEmptyJPanel();
        new MyDropTargetListener(panel);//this must be done or we wont be able to drop any image onto the empty panel

        frame.add(panel, BorderLayout.CENTER);

        try {
            frame.add(createJLabelPanel(), BorderLayout.SOUTH);
        } catch (Exception ex) {
            ex.printStackTrace();
        }

        frame.pack();

        return frame;
    }

    private static JPanel createEmptyJPanel() {
        final JPanel p = new JPanel() {
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(300, 300);
            }
        };
        p.setBorder(new TitledBorder("Drag Image onto this panel"));

        TransferHandler dnd = new TransferHandler() {
            @Override
            public boolean canImport(TransferSupport support) {
                if (!support.isDrop()) {
                    return false;
                }
                //only Strings
                if (!support.isDataFlavorSupported(DataFlavor.imageFlavor)) {
                    return false;
                }
                return true;
            }

            @Override
            public boolean importData(TransferSupport support) {
                if (!canImport(support)) {
                    return false;
                }

                Transferable tansferable = support.getTransferable();
                Icon ico;
                try {
                    ico = (Icon) tansferable.getTransferData(DataFlavor.imageFlavor);
                } catch (Exception e) {
                    e.printStackTrace();
                    return false;
                }
                p.add(new JLabel(ico));
                return true;
            }
        };

        p.setTransferHandler(dnd);

        return p;
    }

    private static JPanel createJLabelPanel() throws Exception {
        JPanel panel = new JPanel();
        panel.setBorder(new TitledBorder("Drag Image from here to Panel above"));

        JLabel label1 = new JLabel(new ImageIcon(new URL("http://i.stack.imgur.com/gJmeJ.png")));
        JLabel label2 = new JLabel(new ImageIcon(new URL("http://i.stack.imgur.com/8BGfi.png")));
        JLabel label3 = new JLabel(new ImageIcon(new URL("http://i.stack.imgur.com/1lgtq.png")));

        MyDragGestureListener dlistener = new MyDragGestureListener();
        DragSource ds1 = new DragSource();
        ds1.createDefaultDragGestureRecognizer(label1, DnDConstants.ACTION_COPY, dlistener);

        DragSource ds2 = new DragSource();
        ds2.createDefaultDragGestureRecognizer(label2, DnDConstants.ACTION_COPY, dlistener);

        DragSource ds3 = new DragSource();
        ds3.createDefaultDragGestureRecognizer(label3, DnDConstants.ACTION_COPY, dlistener);

        panel.add(label1);
        panel.add(label2);
        panel.add(label3);
        return panel;
    }
}

class MyDropTargetListener extends DropTargetAdapter {

    private DropTarget dropTarget;
    private JPanel p;

    public MyDropTargetListener(JPanel panel) {
        p = panel;
        dropTarget = new DropTarget(panel, DnDConstants.ACTION_COPY, this, true, null);

    }

    @Override
    public void drop(DropTargetDropEvent event) {
        try {
            DropTarget test = (DropTarget) event.getSource();
            Component ca = (Component) test.getComponent();
            Point dropPoint = ca.getMousePosition();
            Transferable tr = event.getTransferable();

            if (event.isDataFlavorSupported(DataFlavor.imageFlavor)) {
                Icon ico = (Icon) tr.getTransferData(DataFlavor.imageFlavor);

                if (ico != null) {

                    p.add(new JLabel(ico));
                    p.revalidate();
                    p.repaint();
                    event.dropComplete(true);
                }
            } else {
                event.rejectDrop();
            }
        } catch (Exception e) {
            e.printStackTrace();
            event.rejectDrop();
        }
    }
}

class MyDragGestureListener implements DragGestureListener {

    @Override
    public void dragGestureRecognized(DragGestureEvent event) {
        JLabel label = (JLabel) event.getComponent();
        final Icon ico = label.getIcon();


        Transferable transferable = new Transferable() {
            @Override
            public DataFlavor[] getTransferDataFlavors() {
                return new DataFlavor[]{DataFlavor.imageFlavor};
            }

            @Override
            public boolean isDataFlavorSupported(DataFlavor flavor) {
                if (!isDataFlavorSupported(flavor)) {
                    return false;
                }
                return true;
            }

            @Override
            public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
                return ico;
            }
        };
        event.startDrag(null, transferable);
    }
}

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