Java Swing Tutorial - Java Swing Drag and Drop








Drag and drop (DnD) is a way to transfer data in an application.

DnD allows us to transfer data by dragging a component and dropping it onto another component.

The component dragged is called the drag source; it supplies the data to be transferred.

The component dropped is called the drop target; it is the receiver of the data.

The data transfer is accomplished using a Transferable object.

Transferable is an interface in the java.awt.datatransfer package.

The Transferable interface contains the following three methods: 

DataFlavor[] getTransferDataFlavors()
boolean isDataFlavorSupported(DataFlavor flavor)
Object getTransferData(DataFlavor flavor)  throws   UnsupportedFlavorException, IOException

To enable the dragging on the component 

myComponent.setDragEnabled(true);

All text components (JFileChooser, JColorChooser, JList, JTree, and JTable) have built-in drag support for DnD.

For example, suppose we have a JTextField named nameFld and a JTextArea named descTxtArea. To start using DnD between them, we need to write the following two lines of code: 

nameFld.setDragEnabled(true);
descTxtArea.setDragEnabled(true);

We can select text in the JTextField, drag it, and drop it onto the JTextArea. The selected text in the JTextField is transferred to the JTextArea. we can also drag text from the JTextArea to the JTextField.

Transfer Actions are represented by the constants declared in the TransferHandler class:

  • TranferHandler.COPY
  • TranferHandler.MOVE
  • TranferHandler.COPY_OR_MOVE
  • TranferHandler.LINK
  • TranferHandler.NONE




Example

The following code shows how to use DnD to Transfer Data Between Swing Components 

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.StringSelection;
import java.awt.datatransfer.Transferable;
//from  ww w  .j  av  a 2 s .c o  m
import javax.swing.Box;
import javax.swing.DefaultListModel;
import javax.swing.DropMode;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.ListSelectionModel;
import javax.swing.SwingUtilities;
import javax.swing.TransferHandler;

public class Main extends JFrame {
  private JTextField newTextField = new JTextField(10);
  private JList<String> sourceList = new JList<>(new DefaultListModel<>());
  private JList<String> destList = new JList<>(new DefaultListModel<>());
  public Main() {
    
    for (int i = 0; i < 15; i++) {
      ((DefaultListModel<String>) sourceList.getModel()).add(i, "A " + i);
      ((DefaultListModel<String>) destList.getModel()).add(i, "B " + i);
    }
    Box nameBox = Box.createHorizontalBox();
    nameBox.add(new JLabel("New:"));
    nameBox.add(newTextField);

    Box sourceBox = Box.createVerticalBox();
    sourceBox.add(new JLabel("Source"));
    sourceBox.add(new JScrollPane(sourceList));

    Box destBox = Box.createVerticalBox();
    destBox.add(new JLabel("Destination"));
    destBox.add(new JScrollPane(destList));

    Box listBox = Box.createHorizontalBox();
    listBox.add(sourceBox);
    listBox.add(destBox);

    Box allBox = Box.createVerticalBox();
    allBox.add(nameBox);
    allBox.add(listBox);

    this.getContentPane().add(allBox, BorderLayout.CENTER);

    sourceList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    destList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

    newTextField.setDragEnabled(true);
    sourceList.setDragEnabled(true);
    destList.setDragEnabled(true);

    sourceList.setDropMode(DropMode.INSERT);
    destList.setDropMode(DropMode.INSERT);

    sourceList.setTransferHandler(new ListTransferHandler());
    destList.setTransferHandler(new ListTransferHandler());
  }
  public static void main(String[] args) {
    SwingUtilities.invokeLater(() -> {
      Main frame = new Main();
      frame.pack();
      frame.setVisible(true);
    });
  }
}
class ListTransferHandler extends TransferHandler {
  @Override
  public int getSourceActions(JComponent c) {
    return TransferHandler.COPY_OR_MOVE;
  }
  @Override
  protected Transferable createTransferable(JComponent source) {
    JList<String> sourceList = (JList<String>) source;
    String data = sourceList.getSelectedValue();
    Transferable t = new StringSelection(data);
    return t;
  }

  @Override
  protected void exportDone(JComponent source, Transferable data, int action) {
    @SuppressWarnings("unchecked")
    JList<String> sourceList = (JList<String>) source;
    String movedItem = sourceList.getSelectedValue();
    if (action == TransferHandler.MOVE) {
      DefaultListModel<String> listModel = (DefaultListModel<String>) sourceList
          .getModel();
      listModel.removeElement(movedItem);
    }
  }
  @Override
  public boolean canImport(TransferHandler.TransferSupport support) {
    if (!support.isDrop()) {
      return false;
    }
    return support.isDataFlavorSupported(DataFlavor.stringFlavor);
  }
  @Override
  public boolean importData(TransferHandler.TransferSupport support) {
    if (!this.canImport(support)) {
      return false;
    }
    Transferable t = support.getTransferable();
    String data = null;
    try {
      data = (String) t.getTransferData(DataFlavor.stringFlavor);
      if (data == null) {
        return false;
      }
    } catch (Exception e) {
      e.printStackTrace();
      return false;
    }
    JList.DropLocation dropLocation = (JList.DropLocation) support
        .getDropLocation();
    int dropIndex = dropLocation.getIndex();
    JList<String> targetList = (JList<String>) support.getComponent();
    DefaultListModel<String> listModel = (DefaultListModel<String>) targetList
        .getModel();
    if (dropLocation.isInsert()) {
      listModel.add(dropIndex, data);
    } else {
      listModel.set(dropIndex, data);
    }
    return true;
  }
}