How to paint the Dropline of a RowHeader-JTable on the Main-JTable during a DragAndDrop?

Question

I\'m using a second JTable in the Viewport of a JScrollPane to build a RowHeader for a main table. DragAndDrop on the main table is disabled. On the rowheader table DnD is enabl

Answer 1

I suggest you to do like this (using Swing's drag & drop functionality):

    RowHeaderTable rowTable = new RowHeaderTable(mainTable);
    rowTable.setAutoscrolls(true);
    rowTable.setDragEnabled(true);
    rowTable.setTransferHandler(new RowHeaderTransferHandler(mainTable));
    rowTable.setDropMode(DropMode.INSERT_ROWS);
    try {
        DropTarget dropTarget = rowTable.getDropTarget();
        dropTarget.addDropTargetListener(rowTable);
    }
    catch(TooManyListenersException e) {
        e.printStackTrace();
    }

Now you have to implement DropTargetListener:

public class RowHeaderTable extends JTable implements ChangeListener, PropertyChangeListener, DropTargetListener {

These are 2 methods that you should be interested in:

    @Override
    public void dragEnter(DropTargetDragEvent dtde) { shouldPaint = true }

    @Override
    public void dragExit(DropTargetEvent dte) { shouldPaint = false }

Now you should manipulate your mainTable (to paint this "green line") using your TranserHandler:

    @Override
    public boolean canImport(TransferSupport supp) {
        DropLocation location = supp.getDropLocation();
        if(location instanceof javax.swing.JTable.DropLocation && shouldPaint) {
            javax.swing.JTable.DropLocation tableLocation = (javax.swing.JTable.DropLocation) location;
            int rowToInsert = tableLocation.getRow();
            //paint somehow the "green line"
            //remember that canImport is invoked when you move your mouse
        }
        return true;
    }

Basically you should implement your own row renderer or something similar (like in @naugler answer). You should somehow provide boolean shouldPaint to your TransferHandler as well. But this is not a big deal to implement.

Hope this helps.