Enable stringFlavor Transfersupport in Java Swing

Question

I am implementing functionality for dragging a JLabels text attribute into JTable cells. So I created my own TransferHandler file for the table. But every challenge

support.isDataFlavorSupported(DataFlavor.stringFlavor) 

returns false

How can I make sure my TransferHandler can import strings?

Here is the source

 public class TableHandler extends TransferHandler { private static final long serialVersionUID = 1L; @Override public boolean canImport(TransferSupport support) { if (!support.isDrop()) { return false; } //only Strings if(!support.isDataFlavorSupported(DataFlavor.stringFlavor)){ return false; } return true; } @Override public boolean importData(TransferSupport support) { if (!canImport(support)) { return false; } Transferable tansferable = support.getTransferable(); String line; try { line = (String) tansferable .getTransferData(DataFlavor.stringFlavor); } catch (Exception e) { return false; } JTable.DropLocation dl = (JTable.DropLocation) support .getDropLocation(); int column = dl.getColumn(); int row = dl.getRow(); String[] data = line.split(","); for (String item : data) { if (!item.isEmpty()) { table.getTableModel().setValueAt(item, row, column); } } return true; } } 

Answer 1

Verify that this example is working fine:

Before any drag and drop of JLabel s:

Click and drag Hello JLabel to cell 1:

When releasing a click on the first cell:

 import java.awt.BorderLayout; import java.awt.datatransfer.DataFlavor; import java.awt.datatransfer.Transferable; import java.awt.datatransfer.UnsupportedFlavorException; import java.awt.dnd.DnDConstants; import java.awt.dnd.DragGestureEvent; import java.awt.dnd.DragGestureListener; import java.awt.dnd.DragSource; import java.io.IOException; import javax.swing.DropMode; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTable; import javax.swing.SwingUtilities; import javax.swing.TransferHandler; public class Test { public static void main(String[] args) { createAndShowJFrame(); } public static void createAndShowJFrame() { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { JFrame frame = createJFrame(); frame.setVisible(true); } }); } private static JFrame createJFrame() { JFrame frame = new JFrame(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setTitle("Test"); JTable table = createJTable(); JScrollPane js = new JScrollPane(table); frame.add(js, BorderLayout.CENTER); frame.add(createJLabelPanel(), BorderLayout.SOUTH); frame.pack(); //frame.setResizable(false);//make it un-resizeable //frame.setLocationRelativeTo(null);//center JFrame return frame; } private static JTable createJTable() { // setup table data String[] columns = new String[]{"Foo", "Bar", "Baz", "Quux"}; String[][] data = new String[][]{{"A", "B", "C", "D"}, {"1", "2", "3", "4"}, {"i", "ii", "iii", "iv"}}; // create table final JTable table = new JTable(data, columns); // set up drag and drop table.setDragEnabled(true); table.setDropMode(DropMode.USE_SELECTION); table.setFillsViewportHeight(true); TransferHandler dnd = new TransferHandler() { @Override public boolean canImport(TransferSupport support) { if (!support.isDrop()) { return false; } //only Strings if (!support.isDataFlavorSupported(DataFlavor.stringFlavor)) { return false; } return true; } @Override public boolean importData(TransferSupport support) { if (!canImport(support)) { return false; } Transferable tansferable = support.getTransferable(); String line; try { line = (String) tansferable.getTransferData(DataFlavor.stringFlavor); } catch (Exception e) { e.printStackTrace(); return false; } JTable.DropLocation dl = (JTable.DropLocation) support.getDropLocation(); int column = dl.getColumn(); int row = dl.getRow(); String[] data = line.split(","); for (String item : data) { if (!item.isEmpty()) { table.getModel().setValueAt(item, row, column); } } return true; } }; table.setTransferHandler(dnd); table.setPreferredScrollableViewportSize(table.getPreferredSize()); return table; } private static JPanel createJLabelPanel() { JPanel panel = new JPanel(); JLabel label1 = new JLabel("Hello"); JLabel label2 = new JLabel("Yay"); JLabel label3 = new JLabel("Bye"); MyDragGestureListener dlistener = new MyDragGestureListener(); DragSource ds1 = new DragSource(); ds1.createDefaultDragGestureRecognizer(label1, DnDConstants.ACTION_COPY, dlistener); DragSource ds2 = new DragSource(); ds2.createDefaultDragGestureRecognizer(label2, DnDConstants.ACTION_COPY, dlistener); DragSource ds3 = new DragSource(); ds3.createDefaultDragGestureRecognizer(label3, DnDConstants.ACTION_COPY, dlistener); panel.add(label1); panel.add(label2); panel.add(label3); return panel; } } class MyDragGestureListener implements DragGestureListener { @Override public void dragGestureRecognized(DragGestureEvent event) { JLabel label = (JLabel) event.getComponent(); final String text = label.getText(); Transferable transferable = new Transferable() { @Override public DataFlavor[] getTransferDataFlavors() { return new DataFlavor[]{DataFlavor.stringFlavor}; } @Override public boolean isDataFlavorSupported(DataFlavor flavor) { if (!isDataFlavorSupported(flavor)) { return false; } return true; } @Override public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException { return text; } }; event.startDrag(null, transferable); } } 

Answer 2

A higher level alternative for David's low level approach (for dragging a shortcut) is to use the in-build property passing on it. It installs by simply installing transferHandler and mouseListener, which starts the export:

 MouseListener listener = new MouseAdapter() { @Override public void mousePressed(MouseEvent e) { JComponent c = (JComponent) e.getSource(); TransferHandler handler = c.getTransferHandler(); handler.exportAsDrag(c, e, TransferHandler.COPY); } }; // a transferHandler configured to export the text property TransferHandler handler = new TransferHandler("text"); JComponent labels = new JPanel(); for (int i = 0; i < 4; i++) { JLabel label1 = new JLabel("item: " + i); label1.addMouseListener(listener); label1.setTransferHandler(handler); labels.add(label1); } 

The payment fee works a little more in TableTransferHandler: now it should check not only for a predetermined string stringFlavor, but also for checkClass for String and accept this:

 public class TableHandlerExt extends TransferHandler { /** * Implemented to return true if the support can provide string values. */ @Override public boolean canImport(TransferSupport support) { if (!support.isDrop()) { return false; } return isStringDataSupported(support); } /** * Returns a boolean indicating whether or not the support can * provide a string value. Checks for predefined DataFlavor.stringFlavor * and flavors with a representationClass of String. */ protected boolean isStringDataSupported(TransferSupport support) { if (support.isDataFlavorSupported(DataFlavor.stringFlavor)) return true; DataFlavor[] flavors = support.getDataFlavors(); for (DataFlavor dataFlavor : flavors) { if (dataFlavor.getRepresentationClass() == String.class) return true; } return false; } @Override public boolean importData(TransferSupport support) { if (!canImport(support)) { return false; } String line; try { line = getStringData(support); } catch (Exception e) { e.printStackTrace(); return false; } JTable table = (JTable) support.getComponent(); JTable.DropLocation dl = (JTable.DropLocation) support.getDropLocation(); int column = dl.getColumn(); int row = dl.getRow(); if (!line.isEmpty()) { // note: we need to use table api to access the table, as the // row/column coordinates are view coordinates table.setValueAt(line, row, column); } return true; } /** * Returns the String provided by the support. * Tries for predefined DataFlavor.stringFlavor * and flavors with a representationClass of String. */ protected String getStringData(TransferSupport support) throws UnsupportedFlavorException, IOException { if (support.isDataFlavorSupported(DataFlavor.stringFlavor)) { return (String) support.getTransferable().getTransferData(DataFlavor.stringFlavor); } DataFlavor[] flavors = support.getDataFlavors(); for (DataFlavor dataFlavor : flavors) { if (dataFlavor.getRepresentationClass() == String.class) { return (String) support.getTransferable().getTransferData(dataFlavor); } } return ""; } }