Name: bsC130419 Date: 07/18/2001


java version "1.4.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta-b65)
Java HotSpot(TM) Client VM (build 1.4.0-beta-b65, mixed mode)

The Swing Data Transfer document included with the docs for 1.4beta states:
"There are four components that do not have default TransferHandlers:
JFileChooser, JList, JTable, and JTree. For these four components, a DropTarget
is installed that indicates a potential insertion point. All that is required
to fully support imports is for the developer to write and install a custom
TransferHandler."

This is not true in the case of JTable.

First of all, there is no indication of a potential insertion point that I can
see while dragging an item into the table.

Secondly, after writing a custom TransferHandler, I realized that a mechanism
is completely lacking by which to determine what cell within a JTable the drop
occurred over. To accomplish this, it is necessary to set a new DropTarget on
the JTable with a custom DropTargetListener that can intercept the drop event
and determine the cursor location at the time of drop.

Either the documentation is incorrect or a facility for determining drop
locations is lacking in the current TransferHandler design.

--------------- code ---------------

import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.dnd.*;
import javax.swing.*;

/**
 * the purpose of this class is to illustrate that adding a custom
 * TransferHandler is NOT sufficient for drop-enabling a JTable
 */
class JTableNoDrop {

    static class TestTransferHandler extends TransferHandler {
        public TestTransferHandler() {
            // we don't want to transfer properties, which is what the
            // superclass does
            super(null);
        }

        public boolean canImport(JComponent comp,DataFlavor[] flavors) {
            // just cheat and return true (accept all imports)
            return true;
        }

        public boolean importData(JComponent comp,Transferable t) {
            System.out.println("TestTransferHandler would import data here...");
            // I could cast comp to a JTable and do setValueAt(row,col) here with
            // the data in t, but how would I know what row & col are? I can't
            // without writing a DropTargetListener, associating it with a new
            // DropTarget, and setting that DropTarget on the JTable.
            return false;
        }

        // the remaining methods in TransferHandler seem to deal with exporting
        // data, so we won't bother overriding them

    }

    public static void main(String[] args) {

        final int SIZE = 5;

        // set up the table to drag from
        Object[][] junkData = new Object[SIZE][SIZE];
        for (int i = 0; i < SIZE; i++) {
            for (int j = 0; j < SIZE; j++) {
                junkData[i][j] = "Object " + (SIZE * (i+j));
            }
        }
        JTable dragTable = new JTable(junkData,new Object[] {"A","B","C","D","E"});
        dragTable.setDragEnabled(true); // this works fine to enable drags

        JLabel label = new JLabel("Try to drag from top table to bottom.");

        JTable dropTable = new JTable(SIZE,SIZE);

        // This will NOT be sufficient for drops
        // There is also NO indication of a "potential drop point" as per the
        // Swing data transfer docs
        dropTable.setTransferHandler(new TestTransferHandler());

        JFrame frame = new JFrame("JTable Drop Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(new BorderLayout());

        frame.getContentPane().add(dragTable,BorderLayout.NORTH);
        frame.getContentPane().add(label,BorderLayout.CENTER);
        frame.getContentPane().add(dropTable,BorderLayout.SOUTH);

        frame.pack();
        frame.setVisible(true);
    }

}

(Review ID: 128358)
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