Java 使用鼠标拖动滚动时暂时禁用或阻止重新绘制JViewPort

我已经编写了一个如下定义的

MouseListener

，这样我可以移动

JButton

来重新排序

JPanel

中的组件。

JPanel

位于

JScrollPane

中，因此当添加多个组件时，可以滚动它们

我遇到的问题是，当拖动组件时，鼠标离开滚动窗格/视口，然后组件将弹回到

JPanel

中的位置，然后将在正确的位置绘制。我假设这种行为是由于当我调用

scrollRectToVisible（）

有什么方法可以防止这种情况发生吗

请注意，我仅限于Java5

听众

import java.awt.Component;
import java.awt.Container;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import javax.swing.JViewport;
import javax.swing.SwingUtilities;
import javax.swing.event.MouseInputAdapter;

public class DragListener extends MouseInputAdapter
{
    private Point location;
    private MouseEvent pressed;
    private MouseEvent dragged;
    private MouseEvent dropped;

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

    @Override
    public void mouseDragged(MouseEvent me)
    {
        dragged = me;
        Component component = dragged.getComponent();
        Container parent = component.getParent();
        Container superParent = parent.getParent();

        if(superParent instanceof JViewport)
        {
            JViewport vp = (JViewport)superParent;
            Rectangle vpb = vp.getBounds();
            Point pt = MouseInfo.getPointerInfo().getLocation();
            SwingUtilities.convertPointFromScreen(pt, vp);

            if(!vpb.contains(pt))
            {
                int yDiff = (pt.y < vpb.y ) ? pt.y : pt.y - vpb.height;
                vpb.translate(0, yDiff);
                vp.scrollRectToVisible(vpb);
            }
        }

        location = component.getLocation(location);
        int x = location.x - pressed.getX() + me.getX();
        int y = location.y - pressed.getY() + me.getY();
        component.setLocation(x, y);
    }

    // Mouse release omitted
}

---

你有两个核心问题，第一个是你试图对抗布局管理器，它会在组件失效时重新布局，第二个是你正在以一种非常奇怪的方式进行拖动过程

当视口的可视区域发生更改时，组件将重新验证，这将导致重新计算组件的位置，使其立即返回到初始位置

此时此刻，你有一个选择，那就是不要它

mainPanel.setLayout(null);
mainPanel.setPreferredSize(new Dimension(200, 600));

// Below Repeated for buttons 1-9 (left out for conciseness)
jButton1.setFont(new java.awt.Font("Tahoma", 1, 48)); // NOI18N
jButton1.setForeground(new java.awt.Color(255, 0, 0));
jButton1.setText("1");
jButton1.setBounds(0, 0, 100, 100);
mainPanel.add(jButton1);

当您引入更多组件时，这将导致问题

您的

mouseDragged

方法也可以被大大简化

@Override
public void mouseDragged(MouseEvent me) {
    JComponent source = (JComponent) me.getComponent();
    JComponent parent = (JComponent) source.getParent();

    Point p = me.getPoint();
    p = SwingUtilities.convertPoint(source, p, parent);

    Rectangle bounds = source.getBounds();
    bounds.setLocation(p);  

    bounds.x -= pressed.getX();
    bounds.y -= pressed.getY();
    source.setBounds(bounds);
    parent.scrollRectToVisible(bounds);
}

更好的解决方案是利用

可转移的
API和/或已经存在的Drag'n'Drop API，基本上将组件从其当前容器中移除，并根据其放置位置将其重新添加到组件层次结构中的不同位置。这允许您继续使用布局管理器；）

例如，看一看

使用DnD示例更新


好的，这个例子借鉴了，但是允许你在组件被放下时“重新定位”。作为一个额外的好处，有一个很好的“指示器”显示组件“应该”出现的位置

因为组件在“导出”时被序列化，这会导致侦听器和
DragGestureRecognizer
出现无休止的问题。为此，我实现了一个
DragDropManager
，其唯一目的是
安装
和
卸载
DragestureHandler
和
DragestureRecognizer
在拖放过程中的某些点……这就是为什么我倾向于传输状态而不是组件的原因：P

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Cursor;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.Rectangle;
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.DragGestureRecognizer;
import java.awt.dnd.DragSource;
import java.awt.dnd.DragSourceDragEvent;
import java.awt.dnd.DragSourceDropEvent;
import java.awt.dnd.DragSourceEvent;
import java.awt.dnd.DragSourceListener;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetContext;
import java.awt.dnd.DropTargetDragEvent;
import java.awt.dnd.DropTargetDropEvent;
import java.awt.dnd.DropTargetEvent;
import java.awt.dnd.DropTargetListener;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class DragginTest extends javax.swing.JFrame {

    public DragginTest() {
        initComponents();
    }

    @SuppressWarnings("unchecked")

    private void initComponents() {
        jScrollPane1 = new javax.swing.JScrollPane();
        mainPanel = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setPreferredSize(new java.awt.Dimension(450, 450));

        mainPanel.setLayout(new GridLayout(10, 0));

        // Below Repeated for buttons 1-9 (left out for conciseness)
        for (int index = 0; index < 10; index++) {
            JButton btn = new JButton(String.valueOf(index));
            btn.setFont(new java.awt.Font("Tahoma", 1, 48)); // NOI18N
            btn.setForeground(new java.awt.Color(255, 0, 0));

            DragDropManager.INSTANCE.installDrag(btn);

            mainPanel.add(btn);
        }
        // End Repeat

        DropHandler dropHandler = new DropHandler();
        DropTarget dropTarget = new DropTarget(mainPanel, DnDConstants.ACTION_MOVE, dropHandler, true);
        mainPanel.setDropTarget(dropTarget);

        jScrollPane1.setViewportView(mainPanel);

        getContentPane().setLayout(new BorderLayout());
        add(jScrollPane1);

        pack();
    }

    public static void main(String args[]) {
        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new DragginTest().setVisible(true);
            }
        });
    }

    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JPanel mainPanel;

    public enum DragDropManager {

        INSTANCE;

        private Map<Component, DragManager> handlers = new HashMap<>(25);

        protected void installDrag(Component comp) {
            handlers.put(comp, new DragManager(comp));
        }

        protected void uninstallDrag(Component comp) {
            DragManager manager = handlers.remove(comp);
            if (manager != null) {
                manager.uninstall();
            }
        }

        protected class DragManager {

            DragGestureHandler dragGestureHandler;
            DragGestureRecognizer dgr;

            public DragManager(Component comp) {
                dragGestureHandler = new DragGestureHandler(comp);
                dgr = DragSource.getDefaultDragSource().createDefaultDragGestureRecognizer(
                                comp,
                                DnDConstants.ACTION_MOVE,
                                dragGestureHandler);
            }

            public void uninstall() {
                dgr.removeDragGestureListener(dragGestureHandler);
                dragGestureHandler = null;
                dgr = null;
            }

        }
    }

    public static class ComponentDataFlavor extends DataFlavor {

        // This saves me having to make lots of copies of the same thing
        public static final ComponentDataFlavor SHARED_INSTANCE = new ComponentDataFlavor();

        public ComponentDataFlavor() {

            super(JPanel.class, null);

        }

    }

    public static class ComponentTransferable implements Transferable {

        private DataFlavor[] flavors = new DataFlavor[]{ComponentDataFlavor.SHARED_INSTANCE};
        private Component component;

        public ComponentTransferable(Component panel) {
            this.component = panel;
        }

        @Override
        public DataFlavor[] getTransferDataFlavors() {
            return flavors;
        }

        @Override
        public boolean isDataFlavorSupported(DataFlavor flavor) {

            // Okay, for this example, this is over kill, but makes it easier
            // to add new flavor support by subclassing
            boolean supported = false;

            for (DataFlavor mine : getTransferDataFlavors()) {

                if (mine.equals(flavor)) {

                    supported = true;
                    break;

                }

            }

            return supported;

        }

        public Component getComponent() {

            return component;

        }

        @Override
        public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {

            Object data = null;
            if (isDataFlavorSupported(flavor)) {

                data = getComponent();

            } else {

                throw new UnsupportedFlavorException(flavor);

            }

            return data;

        }

    }

    public static class DragGestureHandler implements DragGestureListener, DragSourceListener {

        private Container parent;
        private final Component component;

        public DragGestureHandler(Component child) {

            this.component = child;

        }

        public Component getComponent() {
            return component;
        }

        public void setParent(Container parent) {
            this.parent = parent;
        }

        public Container getParent() {
            return parent;
        }

        @Override
        public void dragGestureRecognized(DragGestureEvent dge) {

            // When the drag begins, we need to grab a reference to the
            // parent container so we can return it if the drop
            // is rejected
            Container parent = getComponent().getParent();

            setParent(parent);

            // Remove the panel from the parent.  If we don't do this, it
            // can cause serialization issues.  We could over come this
            // by allowing the drop target to remove the component, but that's
            // an argument for another day
            parent.remove(getComponent());

            // Update the display
            parent.invalidate();
            parent.repaint();

            // Create our transferable wrapper
            Transferable transferable = new ComponentTransferable(getComponent());

            // Start the "drag" process...
            DragSource ds = dge.getDragSource();
            ds.startDrag(dge, Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR), transferable, this);

            DragDropManager.INSTANCE.uninstallDrag(getComponent());

        }

        @Override
        public void dragEnter(DragSourceDragEvent dsde) {
        }

        @Override
        public void dragOver(DragSourceDragEvent dsde) {
        }

        @Override
        public void dropActionChanged(DragSourceDragEvent dsde) {
        }

        @Override
        public void dragExit(DragSourceEvent dse) {
        }

        @Override
        public void dragDropEnd(DragSourceDropEvent dsde) {

            // If the drop was not sucessful, we need to
            // return the component back to it's previous
            // parent
            if (!dsde.getDropSuccess()) {

                getParent().add(getComponent());

                getParent().invalidate();
                getParent().repaint();

            }
        }
    }

    public class DropHandler implements DropTargetListener {

        private JComponent spacer = new JPanel();

        public DropHandler() {
            spacer.setBackground(Color.RED);
        }

        @Override
        public void dragEnter(DropTargetDragEvent dtde) {

            // Determine if can actual process the contents comming in.
            // You could try and inspect the transferable as well, but 
            // There is an issue on the MacOS under some circumstances
            // where it does not actually bundle the data until you accept the
            // drop.
            if (dtde.isDataFlavorSupported(ComponentDataFlavor.SHARED_INSTANCE)) {

                dtde.acceptDrag(DnDConstants.ACTION_MOVE);

            } else {

                dtde.rejectDrag();

            }

        }

        @Override
        public void dragOver(DropTargetDragEvent dtde) {

            if (dtde.isDataFlavorSupported(ComponentDataFlavor.SHARED_INSTANCE)) {
                Point p = dtde.getLocation();
                DropTargetContext dtc = dtde.getDropTargetContext();
                Container parent = (Container) dtc.getComponent();
                Component target = parent.getComponentAt(p);
                int insertPoint = Math.max(0, parent.getComponentZOrder(target));
                if (spacer.getParent() == null) {
                    parent.add(spacer, insertPoint);
                } else {
                    parent.setComponentZOrder(spacer, insertPoint);
                }
                parent.revalidate();
                parent.repaint();

                Point pic = SwingUtilities.convertPoint(spacer, p, target);
                Rectangle bounds = spacer.getBounds();
                bounds.setLocation(pic);

                ((JComponent) parent).scrollRectToVisible(bounds);
            }
        }

        @Override
        public void dropActionChanged(DropTargetDragEvent dtde) {
        }

        @Override
        public void dragExit(DropTargetEvent dte) {
            Container parent = (Container) dte.getDropTargetContext().getComponent();
            parent.remove(spacer);
            parent.revalidate();
            parent.repaint();
        }

        @Override
        public void drop(DropTargetDropEvent dtde) {

            boolean success = false;

            // Basically, we want to unwrap the present...
            if (dtde.isDataFlavorSupported(ComponentDataFlavor.SHARED_INSTANCE)) {

                Transferable transferable = dtde.getTransferable();
                try {

                    Object data = transferable.getTransferData(ComponentDataFlavor.SHARED_INSTANCE);
                    if (data instanceof Component) {

                        Component target = (Component) data;

                        DropTargetContext dtc = dtde.getDropTargetContext();
                        Component component = dtc.getComponent();

                        if (component instanceof JComponent) {

                            Container parent = target.getParent();
                            if (parent != null) {

                                parent.remove(target);

                            }
                            parent = (Container) component;

                            Point p = dtde.getLocation();
                            Component before = parent.getComponentAt(p);
                            int insertPoint = Math.max(0, parent.getComponentZOrder(before));
                            parent.remove(spacer);
                            System.out.println(insertPoint);
                            parent.add(target, insertPoint);
                            parent.revalidate();
                            parent.repaint();

                            DragDropManager.INSTANCE.installDrag(target);

                            success = true;
                            dtde.acceptDrop(DnDConstants.ACTION_MOVE);

                            invalidate();
                            repaint();

                        } else {

                            success = false;
                            dtde.rejectDrop();

                        }

                    } else {

                        success = false;
                        dtde.rejectDrop();

                    }

                } catch (Exception exp) {

                    success = false;
                    dtde.rejectDrop();
                    exp.printStackTrace();

                }

            } else {

                success = false;
                dtde.rejectDrop();

            }

            dtde.dropComplete(success);

        }

    }
}

导入java.awt.BorderLayout；
导入java.awt.Color；
导入java.awt.Component；
导入java.awt.Container；
导入java.awt.Cursor；
导入java.awt.GridLayout；
导入java.awt.Point；
导入java.awt.Rectangle；
导入java.awt.datatransfer.DataFlavor；
导入java.awt.datatransfer.transfer；
导入java.awt.datatransfer.UnsupportedFlavorException；
导入java.awt.dnd.DnDConstants；
导入java.awt.dnd.DragGestureEvent；
导入java.awt.dnd.DragGestureListener；
导入java.awt.dnd.DragGestureRecognizer；
导入java.awt.dnd.DragSource；
导入java.awt.dnd.DragSourceDragEvent；
导入java.awt.dnd.DragSourceDropEvent；
导入java.awt.dnd.DragSourceEvent；
导入java.awt.dnd.DragSourceListener；
导入java.awt.dnd.DropTarget；
导入java.awt.dnd.DropTargetContext；
导入java.awt.dnd.dropTargetDrageEvent；
导入java.awt.dnd.DropTargetDropEvent；
导入java.awt.dnd.DropTargetEvent；
导入java.awt.dnd.DropTargetListener；
导入java.io.IOException；
导入java.util.HashMap；
导入java.util.Map；
导入javax.swing.JButton；
导入javax.swing.JComponent；
导入javax.swing.JPanel；
导入javax.swing.SwingUtilities；
公共类DragIntest扩展了javax.swing.JFrame{
公共DragIntest（）{
初始化组件（）；
}
@抑制警告（“未选中”）
私有组件（）{
jScrollPane1=newjavax.swing.JScrollPane（）；
mainPanel=newjavax.swing.JPanel（）；
setDefaultCloseOperation（javax.swing.WindowConstants.EXIT_ON_CLOSE）；
setPreferredSize（新的java.awt.Dimension（450450））；
设置布局（新的网格布局（10,0））；
//按钮1-9重复以下内容（为简洁起见省略）
对于（int-index=0；index<10；index++）{
JButton btn=新的JButton（String.valueOf（index））；
setFont（新的java.awt.Font（“Tahoma”，1，48））；//NOI18N
set前台（新java.awt.Color（255,0,0））；
DragDropManager.INSTANCE.installDrag（btn）；
主面板。添加（btn）；
}
//结束重复
DropHandler DropHandler=新的DropHandler（）；
DropTarget DropTarget=新的DropTarget（主面板，DnDConstants.ACTION\u MOVE，dropHandler，true）；
主面板。设置dropTarget（dropTarget）；
jScrollPane1.setViewportView（主面板）；
getContentPane（）.setLayout（新的BorderLayout（））；
添加（jScrollPane1）；
包装（）；
}
公共静态void main（字符串参数[]）{
/*创建并显示表单*/
invokeLater（new Runnable（））{
公开募捐{
新建DragIntest（）.setVisible（true）；
}
});
}
私有javax.swing.JScrollPane-jScrollPane1；
私有javax.swing.JPanel主面板；
公共枚举DragDropManager{
实例；
私有映射处理程序=新HashMap（25）；
受保护的无效安装拖动（组件组件组件）{
put（comp，新DragManager（comp））；
}
受保护的组件（组件组件组件）{
DragManager=handlers.remove（comp）；
if（manager！=null）{
manager.uninstall（）；
}
}
受保护类DragManager{
DragGestureHandler DragGestureHandler；
Draggesturererecognizer dgr；
公共排水管（公司）
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Cursor;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.Rectangle;
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.DragGestureRecognizer;
import java.awt.dnd.DragSource;
import java.awt.dnd.DragSourceDragEvent;
import java.awt.dnd.DragSourceDropEvent;
import java.awt.dnd.DragSourceEvent;
import java.awt.dnd.DragSourceListener;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetContext;
import java.awt.dnd.DropTargetDragEvent;
import java.awt.dnd.DropTargetDropEvent;
import java.awt.dnd.DropTargetEvent;
import java.awt.dnd.DropTargetListener;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class DragginTest extends javax.swing.JFrame {

    public DragginTest() {
        initComponents();
    }

    @SuppressWarnings("unchecked")

    private void initComponents() {
        jScrollPane1 = new javax.swing.JScrollPane();
        mainPanel = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setPreferredSize(new java.awt.Dimension(450, 450));

        mainPanel.setLayout(new GridLayout(10, 0));

        // Below Repeated for buttons 1-9 (left out for conciseness)
        for (int index = 0; index < 10; index++) {
            JButton btn = new JButton(String.valueOf(index));
            btn.setFont(new java.awt.Font("Tahoma", 1, 48)); // NOI18N
            btn.setForeground(new java.awt.Color(255, 0, 0));

            DragDropManager.INSTANCE.installDrag(btn);

            mainPanel.add(btn);
        }
        // End Repeat

        DropHandler dropHandler = new DropHandler();
        DropTarget dropTarget = new DropTarget(mainPanel, DnDConstants.ACTION_MOVE, dropHandler, true);
        mainPanel.setDropTarget(dropTarget);

        jScrollPane1.setViewportView(mainPanel);

        getContentPane().setLayout(new BorderLayout());
        add(jScrollPane1);

        pack();
    }

    public static void main(String args[]) {
        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new DragginTest().setVisible(true);
            }
        });
    }

    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JPanel mainPanel;

    public enum DragDropManager {

        INSTANCE;

        private Map<Component, DragManager> handlers = new HashMap<>(25);

        protected void installDrag(Component comp) {
            handlers.put(comp, new DragManager(comp));
        }

        protected void uninstallDrag(Component comp) {
            DragManager manager = handlers.remove(comp);
            if (manager != null) {
                manager.uninstall();
            }
        }

        protected class DragManager {

            DragGestureHandler dragGestureHandler;
            DragGestureRecognizer dgr;

            public DragManager(Component comp) {
                dragGestureHandler = new DragGestureHandler(comp);
                dgr = DragSource.getDefaultDragSource().createDefaultDragGestureRecognizer(
                                comp,
                                DnDConstants.ACTION_MOVE,
                                dragGestureHandler);
            }

            public void uninstall() {
                dgr.removeDragGestureListener(dragGestureHandler);
                dragGestureHandler = null;
                dgr = null;
            }

        }
    }

    public static class ComponentDataFlavor extends DataFlavor {

        // This saves me having to make lots of copies of the same thing
        public static final ComponentDataFlavor SHARED_INSTANCE = new ComponentDataFlavor();

        public ComponentDataFlavor() {

            super(JPanel.class, null);

        }

    }

    public static class ComponentTransferable implements Transferable {

        private DataFlavor[] flavors = new DataFlavor[]{ComponentDataFlavor.SHARED_INSTANCE};
        private Component component;

        public ComponentTransferable(Component panel) {
            this.component = panel;
        }

        @Override
        public DataFlavor[] getTransferDataFlavors() {
            return flavors;
        }

        @Override
        public boolean isDataFlavorSupported(DataFlavor flavor) {

            // Okay, for this example, this is over kill, but makes it easier
            // to add new flavor support by subclassing
            boolean supported = false;

            for (DataFlavor mine : getTransferDataFlavors()) {

                if (mine.equals(flavor)) {

                    supported = true;
                    break;

                }

            }

            return supported;

        }

        public Component getComponent() {

            return component;

        }

        @Override
        public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {

            Object data = null;
            if (isDataFlavorSupported(flavor)) {

                data = getComponent();

            } else {

                throw new UnsupportedFlavorException(flavor);

            }

            return data;

        }

    }

    public static class DragGestureHandler implements DragGestureListener, DragSourceListener {

        private Container parent;
        private final Component component;

        public DragGestureHandler(Component child) {

            this.component = child;

        }

        public Component getComponent() {
            return component;
        }

        public void setParent(Container parent) {
            this.parent = parent;
        }

        public Container getParent() {
            return parent;
        }

        @Override
        public void dragGestureRecognized(DragGestureEvent dge) {

            // When the drag begins, we need to grab a reference to the
            // parent container so we can return it if the drop
            // is rejected
            Container parent = getComponent().getParent();

            setParent(parent);

            // Remove the panel from the parent.  If we don't do this, it
            // can cause serialization issues.  We could over come this
            // by allowing the drop target to remove the component, but that's
            // an argument for another day
            parent.remove(getComponent());

            // Update the display
            parent.invalidate();
            parent.repaint();

            // Create our transferable wrapper
            Transferable transferable = new ComponentTransferable(getComponent());

            // Start the "drag" process...
            DragSource ds = dge.getDragSource();
            ds.startDrag(dge, Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR), transferable, this);

            DragDropManager.INSTANCE.uninstallDrag(getComponent());

        }

        @Override
        public void dragEnter(DragSourceDragEvent dsde) {
        }

        @Override
        public void dragOver(DragSourceDragEvent dsde) {
        }

        @Override
        public void dropActionChanged(DragSourceDragEvent dsde) {
        }

        @Override
        public void dragExit(DragSourceEvent dse) {
        }

        @Override
        public void dragDropEnd(DragSourceDropEvent dsde) {

            // If the drop was not sucessful, we need to
            // return the component back to it's previous
            // parent
            if (!dsde.getDropSuccess()) {

                getParent().add(getComponent());

                getParent().invalidate();
                getParent().repaint();

            }
        }
    }

    public class DropHandler implements DropTargetListener {

        private JComponent spacer = new JPanel();

        public DropHandler() {
            spacer.setBackground(Color.RED);
        }

        @Override
        public void dragEnter(DropTargetDragEvent dtde) {

            // Determine if can actual process the contents comming in.
            // You could try and inspect the transferable as well, but 
            // There is an issue on the MacOS under some circumstances
            // where it does not actually bundle the data until you accept the
            // drop.
            if (dtde.isDataFlavorSupported(ComponentDataFlavor.SHARED_INSTANCE)) {

                dtde.acceptDrag(DnDConstants.ACTION_MOVE);

            } else {

                dtde.rejectDrag();

            }

        }

        @Override
        public void dragOver(DropTargetDragEvent dtde) {

            if (dtde.isDataFlavorSupported(ComponentDataFlavor.SHARED_INSTANCE)) {
                Point p = dtde.getLocation();
                DropTargetContext dtc = dtde.getDropTargetContext();
                Container parent = (Container) dtc.getComponent();
                Component target = parent.getComponentAt(p);
                int insertPoint = Math.max(0, parent.getComponentZOrder(target));
                if (spacer.getParent() == null) {
                    parent.add(spacer, insertPoint);
                } else {
                    parent.setComponentZOrder(spacer, insertPoint);
                }
                parent.revalidate();
                parent.repaint();

                Point pic = SwingUtilities.convertPoint(spacer, p, target);
                Rectangle bounds = spacer.getBounds();
                bounds.setLocation(pic);

                ((JComponent) parent).scrollRectToVisible(bounds);
            }
        }

        @Override
        public void dropActionChanged(DropTargetDragEvent dtde) {
        }

        @Override
        public void dragExit(DropTargetEvent dte) {
            Container parent = (Container) dte.getDropTargetContext().getComponent();
            parent.remove(spacer);
            parent.revalidate();
            parent.repaint();
        }

        @Override
        public void drop(DropTargetDropEvent dtde) {

            boolean success = false;

            // Basically, we want to unwrap the present...
            if (dtde.isDataFlavorSupported(ComponentDataFlavor.SHARED_INSTANCE)) {

                Transferable transferable = dtde.getTransferable();
                try {

                    Object data = transferable.getTransferData(ComponentDataFlavor.SHARED_INSTANCE);
                    if (data instanceof Component) {

                        Component target = (Component) data;

                        DropTargetContext dtc = dtde.getDropTargetContext();
                        Component component = dtc.getComponent();

                        if (component instanceof JComponent) {

                            Container parent = target.getParent();
                            if (parent != null) {

                                parent.remove(target);

                            }
                            parent = (Container) component;

                            Point p = dtde.getLocation();
                            Component before = parent.getComponentAt(p);
                            int insertPoint = Math.max(0, parent.getComponentZOrder(before));
                            parent.remove(spacer);
                            System.out.println(insertPoint);
                            parent.add(target, insertPoint);
                            parent.revalidate();
                            parent.repaint();

                            DragDropManager.INSTANCE.installDrag(target);

                            success = true;
                            dtde.acceptDrop(DnDConstants.ACTION_MOVE);

                            invalidate();
                            repaint();

                        } else {

                            success = false;
                            dtde.rejectDrop();

                        }

                    } else {

                        success = false;
                        dtde.rejectDrop();

                    }

                } catch (Exception exp) {

                    success = false;
                    dtde.rejectDrop();
                    exp.printStackTrace();

                }

            } else {

                success = false;
                dtde.rejectDrop();

            }

            dtde.dropComplete(success);

        }

    }
}

import java.awt.*;
import java.awt.Container;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import javax.swing.JViewport;
import javax.swing.SwingUtilities;
import javax.swing.event.MouseInputAdapter;

public class DragListener extends MouseInputAdapter
{
    private Point location;
    private MouseEvent pressed;
    private MouseEvent dragged;
    private MouseEvent dropped;
    private LayoutManager layout;

    @Override
    public void mousePressed(MouseEvent me)
    {
        pressed = me;
        Component component = me.getComponent();
        Container parent = component.getParent();
        parent.setPreferredSize(parent.getPreferredSize());
        layout = parent.getLayout();
        parent.setLayout(null);
    }

    @Override
    public void mouseDragged(MouseEvent me)
    {
        dragged = me;
        Component component = dragged.getComponent();
        Container parent = component.getParent();
        Container superParent = parent.getParent();

        if(superParent instanceof JViewport)
        {
            JViewport vp = (JViewport)superParent;
            Rectangle vpb = vp.getBounds();
            Point pt = MouseInfo.getPointerInfo().getLocation();
            SwingUtilities.convertPointFromScreen(pt, vp);

            if(!vpb.contains(pt))
            {
                int yDiff = (pt.y < vpb.y ) ? pt.y : pt.y - vpb.height;
                vpb.translate(0, yDiff);
                vp.scrollRectToVisible(vpb);
            }
        }

        location = component.getLocation(location);
        int x = location.x - pressed.getX() + me.getX();
        int y = location.y - pressed.getY() + me.getY();
        component.setLocation(x, y);
    }

    // Mouse release omitted
    @Override
    public void mouseReleased(MouseEvent me)
    {
        Component component = me.getComponent();
        Container parent = component.getParent();
        parent.setPreferredSize( null );
        parent.setLayout(layout);
        parent.validate();
        parent.repaint();
    }
}

import java.awt.*;
import java.awt.Container;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import javax.swing.*;
import javax.swing.SwingUtilities;
import javax.swing.event.MouseInputAdapter;

public class DragListener extends MouseInputAdapter
{
    private Point location;
    private MouseEvent pressed;
    private MouseEvent dragged;
    private MouseEvent dropped;
    private LayoutManager layout;
    private Rectangle originalBounds;
    private int originalZOrder;

    @Override
    public void mousePressed(MouseEvent me)
    {
        pressed = me;
        Component component = me.getComponent();
        Container parent = component.getParent();
        originalBounds = component.getBounds();
        originalZOrder = parent.getComponentZOrder(component);
        parent.setPreferredSize(parent.getPreferredSize());
        layout = parent.getLayout();
        parent.setLayout(null);
        parent.setComponentZOrder(component, 0);
    }

    @Override
    public void mouseDragged(MouseEvent me)
    {
        JComponent source = (JComponent) me.getComponent();
        JComponent parent = (JComponent) source.getParent();

        Point p = me.getPoint();
        p = SwingUtilities.convertPoint(source, p, parent);

        Rectangle bounds = source.getBounds();
        bounds.setLocation(p);

        bounds.x -= pressed.getX();
        bounds.y -= pressed.getY();
        source.setLocation(0, bounds.y);
        parent.scrollRectToVisible(bounds);
    }

    @Override
    public void mouseReleased(MouseEvent me)
    {
        boolean moved = false;
        Component component = me.getComponent();
        Container parent = component.getParent();
        Point location = component.getLocation();

        if (location.y < 0)
        {
            parent.add(component, 0);
            moved = true;
        }
        else
        {
            for (int i = 0; i < parent.getComponentCount(); i++)
            {
                Component c = parent.getComponent(i);
                Rectangle bounds = c.getBounds();

                if (c == component)
                    bounds = originalBounds;

                //  Component is released in the space originally occupied
                //  by the component or over an existing component

                if (bounds.contains(0, location.y))
                {
                    if (c == component)
                    {
                        parent.setComponentZOrder(component, originalZOrder);
                    }
                    else
                    {
                        parent.add(component, i);
                    }

                    moved = true;
                    break;
                }
            }
        }

        //  Component is positioned below all components in the container

        if (!moved)
        {
            parent.add(component, parent.getComponentCount() - 1);
        }

        //  Restore layout manager

        parent.setPreferredSize( null );
        parent.setLayout(layout);
        parent.validate();
        parent.repaint();
        component.requestFocusInWindow();
    }

    private static void createAndShowGUI()
    {
        JPanel panel = new JPanel( new GridLayout(0, 1) );
        DragListener drag = new DragListener();

        for (int i = 0; i <10; i++)
        {
            JButton button = new JButton("" + i);
            button.setFont(new java.awt.Font("Tahoma", 1, 48));
            button.setForeground(new java.awt.Color(255, 0, 0));
            button.addMouseListener(drag);
            button.addMouseMotionListener(drag);
            panel.add( button );
        }

        JFrame frame = new JFrame("SSCCE");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add( new JScrollPane(panel) );
        frame.setLocationByPlatform( true );
        frame.setSize(200, 400);
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowGUI();
            }
        });
    }
}