Enable drop just for specific targets in Swing

问题

I'm trying to implement drag & drop in java with two JList instances. The basic flow works fine. However, when I'm dragging a string from one list, I want to restrict the drop target only for the second list. I noticed that when I'm dragging a string from one list to my desktop so it creates a file containing this string.

Is there any way to avoid such situations?

public class SampleDnD extends JFrame{

    public static void main(String[] args) {
        new SampleDnD();

    }
    /**
     * new form of frame sample contain 2 JLists with drag enabled.
     */
    public SampleDnD(){
        JList l1 = new JList();
        JList l2 = new JList();
        JScrollPane jScrollPane1 = new javax.swing.JScrollPane();
        JScrollPane jScrollPane2 = new javax.swing.JScrollPane();
        DefaultListModel listModel1 = new DefaultListModel();
        DefaultListModel listModel2 = new DefaultListModel();

        String[] list1 = new String[]{"1","3","5","7","9"};
        String [] list2 = new String[]{"0","2","4","6","8"};
        for(int index=0;index<list1.length;index++){
            listModel1.add(index, list1[index]);
            listModel2.add(index, list2[index]);
        }
        l1.setModel(listModel1);
        l2.setModel(listModel2);
        l1.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        l2.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        l1.setDropMode(DropMode.INSERT);
        l1.setDragEnabled(true);
        l2.setDragEnabled(true);
        l1.setTransferHandler(new ListTransferHandler());
        l2.setDropMode(DropMode.INSERT);
        l2.setTransferHandler(new ListTransferHandler());
        jScrollPane1.setViewportView(l1);
        jScrollPane2.setViewportView(l2);

        Container cp = getContentPane();
        cp.setLayout(new BoxLayout(cp,BoxLayout.Y_AXIS));
        setPreferredSize(new Dimension(800,500));
        getContentPane().add(jScrollPane1);
        getContentPane().add(jScrollPane2);
        setVisible(true);
        pack();

    }
    public class ListTransferHandler extends TransferHandler {


        /**
         * We only support importing strings.
         */
        public boolean canImport(TransferHandler.TransferSupport info) {
            // Check for String flavor
            if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) {
                return false;
            }
            return true;
       }

        /**
         * Bundle up the selected items in a single list for export.
         * 
         */
        protected Transferable createTransferable(JComponent c) {
            JList list = (JList)c;
            String value = (String)list.getSelectedValue();
            return new StringSelection(value);
        }

        /**
         * We support only move actions.
         */
        public int getSourceActions(JComponent c) {
            return TransferHandler.MOVE;
        }
        /**
         * Perform the actual import.  This demo only supports drag and drop.
         */
        public boolean importData(TransferHandler.TransferSupport info) {
            if (!info.isDrop()) {
                return false;
            }
            JList list = (JList)info.getComponent();
            DefaultListModel listModel = (DefaultListModel)list.getModel();
            JList.DropLocation dl = (JList.DropLocation)info.getDropLocation();
            int index = dl.getIndex();
            boolean insert = dl.isInsert();
            // Get the string that is being dropped.
            Transferable t = info.getTransferable();
            String data;
            try {
                data = (String)t.getTransferData(DataFlavor.stringFlavor);
            } 
            catch (Exception e) { return false; }

            if (insert) {
                listModel.add(index++, data);
            } else {
                // If the items go beyond the end of the current
                // list, add them in.
                if (index < listModel.getSize()) {
                    listModel.set(index++, data);
                } else {
                    listModel.add(index++, data);
                }
            }
            return true;
        }
        /**
         * Remove the items moved from the list.
         */
        protected void exportDone(JComponent c, Transferable data, int action) {
            JList source = (JList)c;
            DefaultListModel listModel  = (DefaultListModel)source.getModel();
            if(action == TransferHandler.MOVE)
            {
                listModel.remove(source.getSelectedIndex());
            }
        }

    }
}

回答1:

A little late, but maybe helpful for somebody else: You need to create your own DatFlavor, that will only be accepted by your own application.

DataFlavor myObjectDataFlavor = new DataFlavor(MyObject.class, "java/MyObject");

Pass this one instead of a default DataFlavor.javaFileListFlavor or DataFlavor.stringFlavor. Your class MyObject is a Pojo containing only a class variable of type String or an integer or whatever you need.

来源：https://stackoverflow.com/questions/14043897/enable-drop-just-for-specific-targets-in-swing