问题
I am implementing a functionality to Drag and Drop the Textattribute of JLabels into the cells of a JTable. So I've created a custom TransferHandler for the table. But every call of
support.isDataFlavorSupported(DataFlavor.stringFlavor)
returns false
How can I make sure that my TransferHandler is able to 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;
}
}
回答1:
Check this example seems to work fine:
Before any dragging / dropping of JLabels:
Clicked and dragged Hello JLabel to 1st cell:
On release of click over 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);
}
}
回答2:
An higher-level alternative to David's low-level approach (for the drag off the label), is to use the in-build property transfer on it. It's installed by simply setting the transferHandler and a mouseListener which triggers 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 price to pay is slightly more work in the TableTransferHandler: it now has to check not only against the pre-defined stringFlavor but check the representationClass against String and accept that as well:
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 "";
}
}
来源：https://stackoverflow.com/questions/17297481/enable-stringflavor-of-transfersupport-in-java-swing