找到了一个简洁的样本，它真正有助于说明DnD在从列表中拖动值并将其放在面板上时的工作原理。
此示例获取列表值的副本。
我已经修改了示例以添加JButton。我可以将它放到面板上，但它移动它而不是制作副本。
为什么JButton被移动而不是复制有什么特定的东西？ 复制按钮而不是移动按钮需要进行哪些更改？ 我甚至尝试按下CTRL键，因为我拖动按钮但仍然移动它而不是复制。
import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.dnd.*;
import java.io.IOException;
import javax.swing.*;
public class TestDnD {
public static void main(String[] args) {
new TestDnD();
}
public TestDnD() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException ex) {
} catch (InstantiationException ex) {
} catch (IllegalAccessException ex) {
} catch (UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private JList list;
public TestPane() {
setLayout(new BorderLayout());
list = new JList();
DefaultListModel model = new DefaultListModel();
model.addElement(new User("Shaun"));
model.addElement(new User("Andy"));
model.addElement(new User("Luke"));
model.addElement(new User("Han"));
model.addElement(new User("Liea"));
model.addElement(new User("Yoda"));
list.setModel(model);
add(new JScrollPane(list), BorderLayout.WEST);
//Without this call, the application does NOT recognize a drag is happening on the LIST.
DragGestureRecognizer dgr = DragSource.getDefaultDragSource().createDefaultDragGestureRecognizer(
list,
DnDConstants.ACTION_COPY_OR_MOVE,
new DragGestureHandler(list)); ///DragGestureHandler - is defined below
///and really just implements DragGestureListener
///and the implemented method defines what is being transferred.
JPanel panel = new JPanel(new GridBagLayout());
add(panel);
//This registers the Target (PANEL) where the Drop is to occur.
DropTarget dt = new DropTarget(
panel,
DnDConstants.ACTION_COPY_OR_MOVE,
new DropTargetHandler(panel), ////DropTargetHandler - is defined below
true); ///and really just implements DropTargetListener
setupButtonTest();
}
private void setupButtonTest()
{
JButton myButton = new JButton("Drag Drop Me");
add(myButton, BorderLayout.NORTH);
DragGestureRecognizer dgr = DragSource.getDefaultDragSource().createDefaultDragGestureRecognizer(
myButton,
DnDConstants.ACTION_COPY, // ACTION_COPY_OR_MOVE,
new DragGestureHandler(myButton)); ///DragGestureHandler - is defined below
///and really just implements DragGestureListener
///and the implemented method defines what is being transferred.
}
}
public static class User {
private String name;
public User(String name) {
this.name = name;
}
public String getName() {
return name;
}
@Override
public String toString() {
return name;
}
}
////This Class handles the actual item or data being transferred (dragged).
public static class UserTransferable implements Transferable {
public static final DataFlavor JIMS_DATA_FLAVOR = new DataFlavor(User.class, "User");
private User user;
private JButton jbutton;
public UserTransferable(User user) {
this.user = user;
}
public UserTransferable(JButton user) {
this.jbutton = user;
}
@Override
public DataFlavor[] getTransferDataFlavors() {
//Executed as soon as the User Object is dragged.
System.out.println("UserTransferable : getTransferDataFlavors()");
return new DataFlavor[]{JIMS_DATA_FLAVOR};
}
@Override
public boolean isDataFlavorSupported(DataFlavor flavor) {
//This is what is executed once the item is dragged into a JComponent that can accept it.
System.out.println("UserTransferable : isDataFlavorSupported()");
return JIMS_DATA_FLAVOR.equals(flavor);
}
@Override
public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
//Once a Drop is done then this method provides the data to actually drop.
System.out.println("UserTransferable : getTransferData()");
Object value = null;
if (JIMS_DATA_FLAVOR.equals(flavor)) {
if (user != null)
value = user;
else if (jbutton != null)
value = jbutton;
} else {
throw new UnsupportedFlavorException(flavor);
}
return value;
}
}
protected class DragGestureHandler implements DragGestureListener {
private JList list;
private JButton button;
public DragGestureHandler(JList list) {
this.list = list;
}
public DragGestureHandler(JButton list) {
this.button = list;
}
@Override
public void dragGestureRecognized(DragGestureEvent dge) {
//This executes once the dragging starts.
System.out.println("DragGestureHandler : dragGesturRecognized()");
if (dge.getComponent() instanceof JList)
{
Object selectedValue = list.getSelectedValue();
if (selectedValue instanceof User) {
User user = (User) selectedValue;
Transferable t = new UserTransferable(user); ////This is where you define what is being transferred.
DragSource ds = dge.getDragSource();
ds.startDrag(
dge,
null,
t,
new DragSourceHandler());
}
}
else if (dge.getComponent() instanceof JButton)
{
Object selectedValue = dge.getComponent();
if (selectedValue instanceof JButton) {
JButton jb = button;
Transferable t = new UserTransferable(jb); ////This is where you define what is being transferred.
DragSource ds = dge.getDragSource();
ds.startDrag(
dge,
null,
t,
new DragSourceHandler());
}
}
}
}
protected class DragSourceHandler implements DragSourceListener {
public void dragEnter(DragSourceDragEvent dsde) {
//This means you have entered a possible Target.
System.out.println("DragSourceHandler : DragEnter()");
}
public void dragOver(DragSourceDragEvent dsde) {
//Continually executes while the DRAG is hovering over an potential TARGET.
System.out.println("DragSourceHandler : DragOver()");
}
public void dropActionChanged(DragSourceDragEvent dsde) {
}
public void dragExit(DragSourceEvent dse) {
//Executes once the potential target has been exited.
System.out.println("DragSourceHandler : DragExit()");
}
public void dragDropEnd(DragSourceDropEvent dsde) {
//Once the mouse button is lifted to do the drop.
//Executes against any potential drop.
System.out.println("DragSourceHandler : dragDropEnd()");
}
}
protected class DropTargetHandler implements DropTargetListener {
////THESE ARE EXECUTED ONLY WHEN THE MOUSE AND DRAGGED ITEM IS OVER THE TARGET.
private JPanel panel;
public DropTargetHandler(JPanel panel) {
this.panel = panel;
}
public void dragEnter(DropTargetDragEvent dtde) {
System.out.println("DropTargetHandler : dragEnter()");
if (dtde.getTransferable().isDataFlavorSupported(UserTransferable.JIMS_DATA_FLAVOR)) {
//This shows the outline within the TARGET to indicate it will accept the DROP.
System.out.println(" Accept...");
dtde.acceptDrag(DnDConstants.ACTION_COPY_OR_MOVE);
} else {
//If an item is not registered to accept a certain drop this is executed.
System.out.println(" DropTargetHandler : DragEnter() - Else");
dtde.rejectDrag();
}
}
public void dragOver(DropTargetDragEvent dtde) {
//Active while the item is being Dragged over the Target
System.out.println("DropTargetHandler : dragOver()");
}
public void dropActionChanged(DropTargetDragEvent dtde) {
System.out.println("DropTargetHandler : dropActionChanged()");
}
public void dragExit(DropTargetEvent dte) {
//Once the dragged item is taken out of the Target area.
System.out.println("DropTargetHandler : dragExit()");
}
public void drop(DropTargetDropEvent dtde) {
//Once the mouse button is released to do the Drop then this is executed.
System.out.println("DropTargetHandler : drop()");
if (dtde.getTransferable().isDataFlavorSupported(UserTransferable.JIMS_DATA_FLAVOR)) {
Transferable t = dtde.getTransferable();
if (t.isDataFlavorSupported(UserTransferable.JIMS_DATA_FLAVOR)) {
try {
Object transferData = t.getTransferData(UserTransferable.JIMS_DATA_FLAVOR);
if (transferData instanceof User) {
User user = (User) transferData;
dtde.acceptDrop(DnDConstants.ACTION_COPY_OR_MOVE);
panel.add(new JLabel(user.getName()));
panel.revalidate();
panel.repaint();
}
else if (transferData instanceof JButton) {
JButton jb = (JButton) transferData;
dtde.acceptDrop(DnDConstants.ACTION_COPY_OR_MOVE);
panel.add(jb);
panel.revalidate();
panel.repaint();
}
else {
dtde.rejectDrop();
}
} catch (UnsupportedFlavorException ex) {
ex.printStackTrace();
dtde.rejectDrop();
} catch (IOException ex) {
ex.printStackTrace();
dtde.rejectDrop();
}
} else {
dtde.rejectDrop();
}
}
}
}
}