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

My solution uses a slightly different approach since we want to add some custom painting on top of existing components. Therefore, I chose to use GlassPane and do the painting there. This way the highlight could be all you can imagine and its size is not limited to cell size, as it could be with an approach using, for example, a cell renderer.

To run this sample you need to download the FinalGlassPane from this site. It is required since we use its capability to capture events (which with regular GlassPane would be consumed). It could be avoided all together if you know a different way to capture the event when the drag is finally over. If you know one please do share. For me this worked best plus I like to have a GlassPane which can capture events and doesn't consume them all.

import java.awt.*;
import java.awt.datatransfer.StringSelection;
import java.awt.datatransfer.Transferable;
import java.awt.dnd.*;
import java.awt.event.AWTEventListener;
import java.awt.event.MouseEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.table.DefaultTableCellRenderer;
import javax.swing.table.JTableHeader;
import javax.swing.table.TableColumn;

public class DNDLinePainterExampleMain extends JFrame {

    public int x = -1;
    public int y = -1;
    private boolean isDragged = false;
    public FinalGlassPane glassPane;
    private boolean isOutsideTable = false;

    public DNDLinePainterExampleMain() {
        final JTable mainTable = new JTable(4, 3);
        mainTable.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);

        final JTable rowTable = new RowHeaderTable(mainTable);
        rowTable.setAutoscrolls(true);
        rowTable.setDragEnabled(true);
        rowTable.setTransferHandler(new RowHeaderTransferHandler());
        rowTable.setDropMode(DropMode.INSERT_ROWS);
        final JScrollPane scrollPane = new JScrollPane(mainTable);
        scrollPane.setRowHeaderView(rowTable);
        scrollPane.setCorner(JScrollPane.UPPER_LEFT_CORNER,
                rowTable.getTableHeader());

        final JPanel panel = new JPanel();

        DragSourceMotionListener dsml = new DragSourceMotionListener() {

            @Override
            public void dragMouseMoved(DragSourceDragEvent dsde) {
                isDragged = true;
                isOutsideTable = true;
                Component source = dsde.getDragSourceContext().getComponent();
                //the coordinates of the drag event in screen coords
                Point toConvert = new Point(dsde.getX(), dsde.getY());
                //convert to source coords
                SwingUtilities.convertPointFromScreen(toConvert, source);
                int rowMargin = rowTable.getRowMargin();
                Point toTest = new Point(toConvert.x, toConvert.y);
                for (int i = 0; i < rowTable.getRowCount(); i++) {
                    Rectangle bounds = rowTable.getCellRect(i, 0, true);
                    boolean isIn = bounds.contains(toTest);
//                    System.out.println("bounds = "+bounds+";  rowMargin = "+rowMargin+";  i = "+i+";  isIn = "+isIn);
                    if (isIn) {
                        isOutsideTable = false;
                        int hHalf = bounds.height / 2;
                        int hIn = toTest.y - bounds.y;
                        boolean isTop = false;
                        if (hIn < hHalf) {
                            isTop = true;
                        }
                        x = bounds.width;
                        y = bounds.y - rowMargin;
                        if (!isTop) {
                            y += bounds.height;
                        }
                        //now convert the point to the glass pane coordinates
                        Point c = SwingUtilities.convertPoint(rowTable, x, y, glassPane);
                        x = c.x;
                        y = c.y;
//                        System.out.println("hIn = "+hIn+";  isTop = "+isTop + "");
                    }
                }
                glassPane.repaint();
            }
        };
        DragSource ds = new DragSource();
        ds.addDragSourceMotionListener(dsml);


        this.setContentPane(panel);
        panel.add(new JButton("Oi for testing"));
        panel.add(scrollPane);


        DragSource dragSource = DragSource.getDefaultDragSource();
        dragSource.addDragSourceMotionListener(dsml);
        glassPane = new FinalGlassPane(this) {

            @Override
            public void eventDispatched(AWTEvent event) {
                super.eventDispatched(event);
                if (event instanceof MouseEvent) {
                    //after drag is relesed we are back here with mouse entered event
                    if (isDragged) {
                        isDragged = false;
                        repaint();
                    }
                }
            }

            @Override
            protected void paintComponent(Graphics g) {
                Graphics2D g2 = (Graphics2D) g;
                if (isDragged && !isOutsideTable) {
                    g2.setPaint(Color.GREEN);
                    g2.drawLine(x + 2, y + 1, x + mainTable.getWidth() - 4, y + 1);
                    g2.drawLine(x, y, x + mainTable.getWidth(), y);
                    g2.drawLine(x + 2, y - 1, x + mainTable.getWidth() - 4, y - 1);
                }
            }
        };
        AWTEventListener al = (AWTEventListener) glassPane;
        Toolkit.getDefaultToolkit().addAWTEventListener(al,
                AWTEvent.MOUSE_MOTION_EVENT_MASK | AWTEvent.MOUSE_EVENT_MASK);

        this.setGlassPane(glassPane);
        glassPane.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame f = new DNDLinePainterExampleMain();
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.pack();
                f.setVisible(true);
            }
        });
    }


    /*
     * Use a JTable as a renderer for row numbers of a given main table. This
     * table must be added to the row header of the scrollpane that contains the
     * main table. from:
     * http://tips4java.wordpress.com/2008/11/18/row-number-table/
     */
    public class RowHeaderTable extends JTable implements ChangeListener,
            PropertyChangeListener {

        private final JTable table;

        public RowHeaderTable(JTable table) {
            this.table = table;
            table.addPropertyChangeListener(this);

            setFocusable(false);
            setAutoCreateColumnsFromModel(false);

            updateRowHeight();
            updateModel();
            updateSelectionModel();

            TableColumn column = new TableColumn();
            column.setHeaderValue("");
            addColumn(column);
            column.setCellRenderer(new RowNumberRenderer());

            getColumnModel().getColumn(0).setPreferredWidth(50);
            setPreferredScrollableViewportSize(getPreferredSize());

            getTableHeader().setReorderingAllowed(false);
        }

        @Override
        public void addNotify() {
            super.addNotify();
            Component c = getParent();
            // Keep scrolling of the row table in sync with the main table.
            if (c instanceof JViewport) {
                JViewport viewport = (JViewport) c;
                viewport.addChangeListener(this);
            }
        }

        /*
         * Delegate method to main table
         */
        @Override
        public int getRowCount() {
            return table.getRowCount();
        }

        @Override
        public int getRowHeight(int row) {
            return table.getRowHeight(row);
        }

        /*
         * This table does not use any data from the main TableModel, so just
         * return a value based on the row parameter.
         */
        @Override
        public Object getValueAt(int row, int column) {
            return Integer.toString(row + 1);
        }
        /*
         * Don't edit data in the main TableModel by mistake
         */

        @Override
        public boolean isCellEditable(int row, int column) {
            return false;
        }
        // implements ChangeListener

        @Override
        public void stateChanged(ChangeEvent e) {
            // Keep the scrolling of the row table in sync with main table
            JViewport viewport = (JViewport) e.getSource();
            JScrollPane scrollPane = (JScrollPane) viewport.getParent();
            scrollPane.getVerticalScrollBar().setValue(viewport.getViewPosition().y);
        }
        // implements PropertyChangeListener

        @Override
        public void propertyChange(PropertyChangeEvent e) {
            // Keep the row table in sync with the main table
            if ("rowHeight".equals(e.getPropertyName())) {
                updateRowHeight();
            }

            if ("selectionModel".equals(e.getPropertyName())) {
                updateSelectionModel();
            }

            if ("model".equals(e.getPropertyName())) {
                updateModel();
            }
        }

        private void updateRowHeight() {
            setRowHeight(table.getRowHeight());
        }

        private void updateModel() {
            setModel(table.getModel());
        }

        private void updateSelectionModel() {
            setSelectionModel(table.getSelectionModel());
        }
        /*
         * Borrow the renderer from JDK1.4.2 table header
         */

        private class RowNumberRenderer extends DefaultTableCellRenderer {

            public RowNumberRenderer() {
                setHorizontalAlignment(JLabel.CENTER);
            }

            @Override
            public Component getTableCellRendererComponent(JTable table,
                    Object value, boolean isSelected, boolean hasFocus, int row,
                    int column) {
                if (table != null) {
                    JTableHeader header = table.getTableHeader();

                    if (header != null) {
                        setForeground(header.getForeground());
                        setBackground(header.getBackground());
                        setFont(header.getFont());
                    }
                }
                if (isSelected) {
                    setFont(getFont().deriveFont(Font.BOLD));
                }
                setText((value == null) ? "" : value.toString());
                setBorder(UIManager.getBorder("TableHeader.cellBorder"));
                return this;
            }
        }//class RowNumberRenderer
    }//class RowHeaderTable

    public class RowHeaderTransferHandler extends TransferHandler {

        @Override
        public int getSourceActions(JComponent c) {
            return COPY_OR_MOVE;
        }

        @Override
        protected Transferable createTransferable(JComponent c) {
            return new StringSelection(c.getName());
        }

        @Override
        public boolean canImport(TransferSupport supp) {
            return true;
        }
    }//class RowHeaderTransferHandler
}