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POWhy is canImport() not called anymore after setDropTarget()?
 

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  1. POWhy is canImport() not called anymore after setDropTarget()?
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    <p>I am experimenting with drag&amp;drop features of JList in Java SE 7. The problem is, that the canImport() method in my TransferHandler implementation stops being called as soon as I set my DropTarget for the JList. Here's the simplified code to demonstrate the issue:</p> <p>main-class:</p> <pre><code>import javax.swing.ListSelectionModel; public class TestDragDrop extends javax.swing.JFrame { public TestDragDrop() { initComponents(); lstTest.setDragEnabled(true); lstTest.setTransferHandler(new MyTransferHandler()); // try to comment and uncomment the following line: lstTest.setDropTarget(new MyDropTarget()); // - commented =&gt; canImport() is called during drag gesture // - uncommented =&gt; canImport() is not called during drag gesture lstTest.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); } @SuppressWarnings("unchecked") // &lt;editor-fold defaultstate="collapsed" desc="Generated Code"&gt; private void initComponents() { scroll1 = new javax.swing.JScrollPane(); lstTest = new javax.swing.JList(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); lstTest.setModel(new javax.swing.AbstractListModel() { String[] strings = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" }; public int getSize() { return strings.length; } public Object getElementAt(int i) { return strings[i]; } }); scroll1.setViewportView(lstTest); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addContainerGap() .addComponent(scroll1, javax.swing.GroupLayout.DEFAULT_SIZE, 249, Short.MAX_VALUE) .addContainerGap()) ); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addContainerGap() .addComponent(scroll1, javax.swing.GroupLayout.DEFAULT_SIZE, 174, Short.MAX_VALUE) .addContainerGap()) ); pack(); }// &lt;/editor-fold&gt; public static void main(String args[]) { new TestDragDrop().setVisible(true); } // Variables declaration - do not modify private javax.swing.JList lstTest; private javax.swing.JScrollPane scroll1; // End of variables declaration } </code></pre> <p>my transfer-handler implementation:</p> <pre><code>import java.awt.datatransfer.Transferable; import javax.swing.JComponent; import javax.swing.JList; import javax.swing.TransferHandler; public class MyTransferHandler extends TransferHandler { @Override public int getSourceActions(JComponent component) { return COPY_OR_MOVE; } @Override protected Transferable createTransferable(JComponent component) { if(component instanceof JList) { return new MyTransferable(new String("TestObject")); } return null; } @Override public boolean canImport(TransferHandler.TransferSupport support) { System.out.println("canImport()"); return true; } @Override public boolean importData(TransferHandler.TransferSupport support) { System.out.println("importData()"); return true; } } </code></pre> <p>my transferable implementation:</p> <pre><code>import java.awt.datatransfer.DataFlavor; import java.awt.datatransfer.Transferable; import java.awt.datatransfer.UnsupportedFlavorException; import java.io.IOException; public class MyTransferable implements Transferable { private final Object object; public MyTransferable(Object object) { this.object = object; } @Override public DataFlavor[] getTransferDataFlavors() { return new DataFlavor[] { DataFlavor.javaFileListFlavor }; } @Override public boolean isDataFlavorSupported(DataFlavor flavor) { return flavor.equals(DataFlavor.javaFileListFlavor); } @Override public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException { if(!isDataFlavorSupported(flavor)) { throw new UnsupportedFlavorException(flavor); } return object; } } </code></pre> <p>my drop-target implementation:</p> <pre><code>import java.awt.dnd.DropTarget; import java.awt.dnd.DropTargetDropEvent; public class MyDropTarget extends DropTarget { @Override public synchronized void drop(DropTargetDropEvent evt) { evt.acceptDrop(evt.getDropAction()); if(evt.isLocalTransfer()) { System.out.println("local transfer"); } else { System.out.println("extern transfer"); } evt.dropComplete(true); } } </code></pre> <p>If the line <strong>lstTest.setDropTarget(new MyDropTarget());</strong> in the main-class is switched-off/commented, the canImport() method in the MyTransferHandler is called during a drag-gesture as expected. But as soon as i uncomment this line, the canImport() method is not being called during dragging...</p> <p>Does someone has any idea why canImport() is not called anymore?</p> <p>Any help highly appreciated! Many thanks in advance.</p>
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