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 enabled. If a Drag on the rowheader is started by the user, I want to extend the painted rowheader dropline (the black line in the image) over the main table (like the green line in the image). Does anybody have an advice for me? Here's the SSCCE: ``` import java.awt.Component; import java.awt.EventQueue; import java.awt.Font; import java.awt.datatransfer.StringSelection; import java.awt.datatransfer.Transferable; import java.beans.PropertyChangeEvent; import java.beans.PropertyChangeListener; import javax.swing.DropMode; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JScrollPane; import javax.swing.JTable; import javax.swing.JViewport; import javax.swing.TransferHandler; import javax.swing.UIManager; import javax.swing.event.ChangeEvent; import javax.swing.eve…

Accepted Answer

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.

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

Solution

Problem