禁用JTable中的拖动选择

Question

Problem

I'd like to click on an unselected cell in a JTable and drag it, ie the table should be in drag mode. The problem is that the JTable has a mechanism that when you click on an unselected cell and drag, you actually aren't in drag mode, but in selection mode. Selection mode should only be possible via click and should be extendable via shift + click, not via dragging.

From what I've found the culprit is in BasicTableUI, but unfortunately everything there that's relevant is private.

Question

How can you prevent selection via dragging and be instantly in drag mode when you click on an unselected cell and drag it?

I searched, but none of the solutions I found were satisfactory. Or they were for older Java versions.

Code

Here's some code for the reproduction:

• Click on an unselected cell and drag the mouse. The cells will be selected.
• Click on a selectged cell and drag. The table is in drag mode.

The code:

import java.awt.BorderLayout;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;

import javax.swing.DropMode;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;

public class Main {
  public static void main(String args[]) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);

    Object rowData[][] = { 
        { "a", "a", "a" }, 
        { "a", "a", "a" }, 
        { "a", "a", "a" }, 
        { "a", "a", "a" }, 
        { "a", "a", "a" }, 
        };

    Object columnNames[] = { "Column 1", "Column 2", "Column 3" };
    final JTable table = new JTable( rowData, columnNames);

    table.setDragEnabled( true);
    table.setDropMode( DropMode.INSERT_ROWS);

    table.addMouseMotionListener( new MouseMotionAdapter() {

      @Override
      public void mouseDragged(MouseEvent e) {

        boolean selectionIsAdjusting = table.getSelectionModel().getValueIsAdjusting();

        if( selectionIsAdjusting) {
          System.out.println("selecting");
        } else {
          System.out.println("dragging");
        }

      }
    });

    table.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
    table.setColumnSelectionAllowed(true);
    table.setRowSelectionAllowed(true);

    JScrollPane scrollPane = new JScrollPane( table);
    frame.add( scrollPane, BorderLayout.CENTER);
    frame.setSize( 300, 150);
    frame.setVisible( true);

  }
}

Screenshot:

Thank you very much for the help!

Answer 1

You might be able to directly call TransferHandler#exportAsDrag(...) method in MouseMotionListener#mouseDragged(...) :

import java.awt.*;
import java.awt.event.*;
import java.util.Optional;
import javax.swing.*;
import javax.swing.table.*;

public class Main2 {
  public JComponent makeUI() {
    Object columnNames[] = {"Column 1", "Column 2", "Column 3"};
    Object data[][] = {
      { "a", "a", "a" },
      { "a", "a", "a" },
      { "a", "a", "a" },
      { "a", "a", "a" },
      { "a", "a", "a" },
    };
    JTable table = new JTable(new DefaultTableModel(data, columnNames));
    table.setDragEnabled(true);
    table.setDropMode(DropMode.INSERT_ROWS);
    table.addMouseMotionListener(new MouseAdapter() {
      @Override public void mouseDragged(MouseEvent e) {
        JComponent c = (JComponent) e.getComponent();
        Optional.ofNullable(c.getTransferHandler())
                .ifPresent(th -> th.exportAsDrag(c, e, TransferHandler.COPY));
      }
    });
    table.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
    table.setColumnSelectionAllowed(true);
    table.setRowSelectionAllowed(true);

    JPanel p = new JPanel(new BorderLayout());
    p.add(new JScrollPane(table));
    p.add(new JTextField(), BorderLayout.SOUTH);
    return p;
  }
  public static void main(String... args) {
    EventQueue.invokeLater(() -> {
      JFrame f = new JFrame();
      f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      f.getContentPane().add(new Main2().makeUI());
      f.setSize(320, 240);
      f.setLocationRelativeTo(null);
      f.setVisible(true);
    });
  }
}

Answer 2

Selection mode should only be possible via click and should be extendable via shift + click, not via dragging

You may be able to alter the behavior by overriding JTable's processMouseEvent method with some additional logic. When a button down event occurs - and shift is not down - alter the selection of the JTable to the current clicked row before calling the parent method.

JTable table = new JTable( rowData, columnNames){
    @Override
        public void processMouseEvent(MouseEvent e){
            Component c = (Component)e.getSource();
            if (e.getModifiersEx() == MouseEvent.BUTTON1_DOWN_MASK  && ( e.getModifiers() & MouseEvent.SHIFT_DOWN_MASK) == 0 ){
                int row = rowAtPoint(e.getPoint());
                int col = columnAtPoint(e.getPoint());
                if ( !isCellSelected(row, col) ){
                     clearSelection();
                     changeSelection(row, col, false, false);
                }

            }
            MouseEvent e1 = new MouseEvent(c, e.getID(), e.getWhen(), 
                    e.getModifiers() | InputEvent.CTRL_MASK, 
                    e.getX(), e.getY(), 
                    e.getClickCount(), 
                    e.isPopupTrigger() , 
                    e.getButton());

            super.processMouseEvent(e1);
        }
};