setDragImage không hoạt động - Java 7

Question

Tôi đang cố gắng thiết lập mã để người dùng có thể kéo từ JTable vào JList và tùy chỉnh hình ảnh kéo bằng cách sử dụng hàm Java 7 setDragImage trong TransferHandler. Tôi lấy một ví dụ trên trang web hướng dẫn java, nơi họ dạy về Drag n Drop, và sau đó thêm một mã "setDragImage". Tuy nhiên nó không hoạt động. Vui lòng xem mã bên dưới và xác định dòng setDragImage() bên trong hàm importData. Tại sao nó không hoạt động?

/* 
* Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved. 
* 
*/ 

import java.util.*; 
import java.awt.*; 
import java.awt.event.*; 
import java.text.*; 
import java.awt.datatransfer.*; 
import java.awt.image.BufferedImage; 

import javax.swing.*; 
import javax.swing.text.*; 
import javax.swing.tree.*; 
import javax.swing.table.*; 

public class BasicDND extends JPanel implements ActionListener { 
    private static JFrame frame; 
    private JTextArea textArea; 
    private JTextField textField; 
    private JList list; 
    private JTable table; 
    private JTree tree; 
    private JColorChooser colorChooser; 
    private JCheckBox toggleDnD; 

    public BasicDND() { 
     super(new BorderLayout()); 
     JPanel leftPanel = createVerticalBoxPanel(); 
     JPanel rightPanel = createVerticalBoxPanel(); 

     //Create a table model. 
     DefaultTableModel tm = new DefaultTableModel(); 
     tm.addColumn("Column 0"); 
     tm.addColumn("Column 1"); 
     tm.addColumn("Column 2"); 
     tm.addColumn("Column 3"); 
     tm.addRow(new String[]{"Table 00", "Table 01", "Table 02", "Table 03"}); 
     tm.addRow(new String[]{"Table 10", "Table 11", "Table 12", "Table 13"}); 
     tm.addRow(new String[]{"Table 20", "Table 21", "Table 22", "Table 23"}); 
     tm.addRow(new String[]{"Table 30", "Table 31", "Table 32", "Table 33"}); 

     //LEFT COLUMN 
     //Use the table model to create a table. 
     table = new JTable(tm); 
     leftPanel.add(createPanelForComponent(table, "JTable")); 

     //Create a color chooser. 
     colorChooser = new JColorChooser(); 
     leftPanel.add(createPanelForComponent(colorChooser, "JColorChooser")); 

     //RIGHT COLUMN 
     //Create a textfield. 
     textField = new JTextField(30); 
     textField.setText("Favorite foods:\nPizza, Moussaka, Pot roast"); 
     rightPanel.add(createPanelForComponent(textField, "JTextField")); 

     //Create a scrolled text area. 
     textArea = new JTextArea(5, 30); 
     textArea.setText("Favorite shows:\nBuffy, Alias, Angel"); 
     JScrollPane scrollPane = new JScrollPane(textArea); 
     rightPanel.add(createPanelForComponent(scrollPane, "JTextArea")); 

     //Create a list model and a list. 
     DefaultListModel listModel = new DefaultListModel(); 
     listModel.addElement("Martha Washington"); 
     listModel.addElement("Abigail Adams"); 
     listModel.addElement("Martha Randolph"); 
     listModel.addElement("Dolley Madison"); 
     listModel.addElement("Elizabeth Monroe"); 
     listModel.addElement("Louisa Adams"); 
     listModel.addElement("Emily Donelson"); 
     list = new JList(listModel); 
     list.setVisibleRowCount(-1); 
     list.getSelectionModel().setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION); 

     list.setTransferHandler(new TransferHandler() { 

      public Image getDragImage() { 
       return null; 
      } 

      @Override 
      public boolean canImport(TransferHandler.TransferSupport info) { 
       // we only import Strings 
       if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) { 
        return false; 
       } 

       JList.DropLocation dl = (JList.DropLocation)info.getDropLocation(); 
       if (dl.getIndex() == -1) { 
        return false; 
       } 
       return true; 
      } 

      public BufferedImage makeImageFromString(String s) { 
       int width = 100; 
       int height = 40; 
       BufferedImage br = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB); 
       Graphics g = br.getGraphics(); 
       g.drawString(s, 0, 0); 
       //g.fillRect(0, 0, width, height); 
       System.out.println("made image from " + s); 
       return br; 
      } 

      @Override 
      public boolean importData(TransferHandler.TransferSupport info) { 
       if (!info.isDrop()) { 
        return false; 
       } 

       // Check for String flavor 
       if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) { 
        displayDropLocation("List doesn't accept a drop of this type."); 
        return false; 
       } 

       JList.DropLocation dl = (JList.DropLocation)info.getDropLocation(); 
       DefaultListModel listModel = (DefaultListModel)list.getModel(); 
       int index = dl.getIndex(); 
       boolean insert = dl.isInsert(); 
       // Get the current string under the drop. 
       String value = (String)listModel.getElementAt(index); 

       // 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; } 

       //HERE IS THE CODE TO SET THE DRAG IMAGE 
       this.setDragImage(makeImageFromString(data)); 

       // Display a dialog with the drop information. 
       String dropValue = "\"" + data + "\" dropped "; 
       if (dl.isInsert()) { 
        if (dl.getIndex() == 0) { 
         displayDropLocation(dropValue + "at beginning of list"); 
        } else if (dl.getIndex() >= list.getModel().getSize()) { 
         displayDropLocation(dropValue + "at end of list"); 
        } else { 
         String value1 = (String)list.getModel().getElementAt(dl.getIndex() - 1); 
         String value2 = (String)list.getModel().getElementAt(dl.getIndex()); 
         displayDropLocation(dropValue + "between \"" + value1 + "\" and \"" + value2 + "\""); 
        } 
       } else { 
        displayDropLocation(dropValue + "on top of " + "\"" + value + "\""); 
       } 

     /** This is commented out for the basicdemo.html tutorial page. 
       ** If you add this code snippet back and delete the 
       ** "return false;" line, the list will accept drops 
       ** of type string. 
       // Perform the actual import. 
       if (insert) { 
        listModel.add(index, data); 
       } else { 
        listModel.set(index, data); 
       } 
       return true; 
     */ 
     return false; 
      } 

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

      @Override 
      protected Transferable createTransferable(JComponent c) { 
       JList list = (JList)c; 
       Object[] values = list.getSelectedValues(); 

       StringBuffer buff = new StringBuffer(); 

       for (int i = 0; i < values.length; i++) { 
        Object val = values[i]; 
        buff.append(val == null ? "" : val.toString()); 
        if (i != values.length - 1) { 
         buff.append("\n"); 
        } 
       } 
       return new StringSelection(buff.toString()); 
      } 
     }); 
     list.setDropMode(DropMode.ON_OR_INSERT); 

     JScrollPane listView = new JScrollPane(list); 
     listView.setPreferredSize(new Dimension(300, 100)); 
     rightPanel.add(createPanelForComponent(listView, "JList")); 

     //Create a tree. 
     DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Mia Familia"); 
     DefaultMutableTreeNode sharon = new DefaultMutableTreeNode("Sharon"); 
     rootNode.add(sharon); 
     DefaultMutableTreeNode maya = new DefaultMutableTreeNode("Maya"); 
     sharon.add(maya); 
     DefaultMutableTreeNode anya = new DefaultMutableTreeNode("Anya"); 
     sharon.add(anya); 
     sharon.add(new DefaultMutableTreeNode("Bongo")); 
     maya.add(new DefaultMutableTreeNode("Muffin")); 
     anya.add(new DefaultMutableTreeNode("Winky")); 
     DefaultTreeModel model = new DefaultTreeModel(rootNode); 
     tree = new JTree(model); 
     tree.getSelectionModel().setSelectionMode 
       (TreeSelectionModel.DISCONTIGUOUS_TREE_SELECTION); 
     JScrollPane treeView = new JScrollPane(tree); 
     treeView.setPreferredSize(new Dimension(300, 100)); 
     rightPanel.add(createPanelForComponent(treeView, "JTree")); 

     //Create the toggle button. 
     toggleDnD = new JCheckBox("Turn on Drag and Drop"); 
     toggleDnD.setActionCommand("toggleDnD"); 
     toggleDnD.addActionListener(this); 

     JSplitPane splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, 
               leftPanel, rightPanel); 
     splitPane.setOneTouchExpandable(true); 

     add(splitPane, BorderLayout.CENTER); 
     add(toggleDnD, BorderLayout.PAGE_END); 
     setBorder(BorderFactory.createEmptyBorder(5,5,5,5)); 
    } 

    protected JPanel createVerticalBoxPanel() { 
     JPanel p = new JPanel(); 
     p.setLayout(new BoxLayout(p, BoxLayout.PAGE_AXIS)); 
     p.setBorder(BorderFactory.createEmptyBorder(5,5,5,5)); 
     return p; 
    } 

    public JPanel createPanelForComponent(JComponent comp, 
              String title) { 
     JPanel panel = new JPanel(new BorderLayout()); 
     panel.add(comp, BorderLayout.CENTER); 
     if (title != null) { 
      panel.setBorder(BorderFactory.createTitledBorder(title)); 
     } 
     return panel; 
    } 

    private void displayDropLocation(final String string) { 
     SwingUtilities.invokeLater(new Runnable() { 
      public void run() { 
       JOptionPane.showMessageDialog(null, string); 
      } 
     }); 
    } 

    public void actionPerformed(ActionEvent e) { 
     if ("toggleDnD".equals(e.getActionCommand())) { 
      boolean toggle = toggleDnD.isSelected(); 
      textArea.setDragEnabled(toggle); 
      textField.setDragEnabled(toggle); 
      list.setDragEnabled(toggle); 
      table.setDragEnabled(toggle); 
      tree.setDragEnabled(toggle); 
      colorChooser.setDragEnabled(toggle); 
     } 
    } 

    /** 
    * Create the GUI and show it. For thread safety, 
    * this method should be invoked from the 
    * event-dispatching thread. 
    */ 
    private static void createAndShowGUI() { 
     //Create and set up the window. 
     frame = new JFrame("BasicDnD"); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

     //Create and set up the content pane. 
     JComponent newContentPane = new BasicDND(); 
     newContentPane.setOpaque(true); //content panes must be opaque 
     frame.setContentPane(newContentPane); 

     //Display the window. 
     frame.pack(); 
     frame.setVisible(true); 
    } 

    public static void main(String[] args) { 
     //Schedule a job for the event-dispatching thread: 
     //creating and showing this application's GUI. 
     javax.swing.SwingUtilities.invokeLater(new Runnable() { 
      public void run() { 
       //Turn off metal's use of bold fonts 
      UIManager.put("swing.boldMetal", Boolean.FALSE); 
       createAndShowGUI(); 
      } 
     }); 
    } 
} 

Answer 1

1. Như Kleopatra nói, loại bỏ getDragImage() {return null; }
2. Move TransferHandler # setDragImage (...) từ IMPORTDATA (...) để getSourceActions (...)
3. Fix makeImageFromString của bạn (...)

---

//As kleopatra says, 
//public Image getDragImage() { 
// return null; 
//} 
public boolean importData(TransferHandler.TransferSupport info) { 
    //... 
    //HERE IS THE CODE TO SET THE DRAG IMAGE 
    //XXX: this.setDragImage(makeImageFromString(data)); 
    //... 
} 
@Override public int getSourceActions(JComponent c) { 
    System.out.println("getSourceActions"); 
    this.setDragImage(makeImageFromString(c)); 
    return COPY; 
} 

FontRenderContext frc = new FontRenderContext(null, true, true); 
JPanel p = new JPanel(); 
public BufferedImage makeImageFromString(JComponent c) { 
    int width = 100; 
    int height = 40; 
    BufferedImage br = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB); 
    Graphics g = br.getGraphics(); 
    g.setColor(Color.RED); 
    g.fillRect(0, 0, width, height); 

//* 
    JList l = (JList)c; 
    ListCellRenderer r = l.getCellRenderer(); 
    Component comp = r.getListCellRendererComponent(
     l, l.getSelectedValue(), l.getSelectedIndex(), false, false); 
    SwingUtilities.paintComponent(g, comp, p, 0, 0, width, height); 
/*/ 
    String s = "aaaa"; 
    Rectangle rect = c.getFont().getStringBounds(s, frc).getBounds(); 
    int tx = (width - rect.width)/2 - rect.x; 
    int ty = (height - rect.height)/2 - rect.y; 
    g.setColor(Color.BLACK); 
    g.drawString(s, tx, ty); 
    System.out.println("made image from " + s); 
//*/ 
    g.dispose(); 
    return br; 
} 

Lưu ý: TransferHandler#setDragImage(java.awt.Image) (Java Platform SE 7)

---

Thêm SSCCE: Cách sử dụng phương thức TransferHandler # setDragImage (...).

import java.util.*; 
import java.awt.*; 
import java.awt.image.*; 
import java.awt.datatransfer.*; 
import javax.swing.*; 
public class BasicDnD { 
    private JList list; 
    public JList makeList() { 
    DefaultListModel<String> m = new DefaultListModel<>(); 
    m.addElement("Martha Washington"); 
    m.addElement("Abigail Adams"); 
    m.addElement("Martha Randolph"); 
    list = new JList<String>(m); 
    list.setTransferHandler(new TransferHandler() { 
     @Override public boolean canImport(TransferHandler.TransferSupport info) { 
     if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) { 
      return false; 
     } 
     JList.DropLocation dl = (JList.DropLocation)info.getDropLocation(); 
     if (dl.getIndex() == -1) { 
      return false; 
     } 
     return true; 
     } 
     @Override public int getSourceActions(JComponent c) { 
     setDragImage(makeImageFromString(c)); 
     return COPY; 
     } 
     private final JPanel p = new JPanel(); 
     private BufferedImage br; 
     private int width, height; 
     private BufferedImage makeImageFromString(JComponent src) { 
     JList l = (JList)src; 
     int idx = l.getSelectedIndex(); 
     Rectangle rect = list.getCellBounds(idx,idx); 
     if(rect==null) return null; 
     if(br==null || rect.width!=width || rect.height!=height) { 
      width = rect.width; 
      height = rect.height; 
      br = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB); 
     } 
     Component c = l.getCellRenderer().getListCellRendererComponent(
      l, l.getSelectedValue(), idx, false, false); 
     Graphics g = br.getGraphics(); 
     g.clearRect(0,0,width,height); 
     SwingUtilities.paintComponent(g, c, p, 0, 0, width, height); 
     g.dispose(); 
     return br; 
     } 
     @Override protected Transferable createTransferable(JComponent c) { 
     JList list = (JList)c; 
     Object[] values = list.getSelectedValues(); 
     StringBuffer buff = new StringBuffer(); 
     for (int i = 0; i < values.length; i++) { 
      Object val = values[i]; 
      buff.append(val == null ? "" : val.toString()); 
      if (i != values.length - 1) { 
      buff.append("\n"); 
      } 
     } 
     return new StringSelection(buff.toString()); 
     } 
    }); 
    list.setDropMode(DropMode.ON_OR_INSERT); 
    list.setDragEnabled(true); 
    return list; 
    } 
    public JComponent makeUI() { 
    JPanel panel = new JPanel(new GridLayout(2,1)); 
    JTextArea textArea = new JTextArea("Drag here from JList!"); 
    panel.add(new JScrollPane(textArea)); 
    panel.add(new JScrollPane(makeList())); 
    return panel; 
    } 
    private static void createAndShowGUI() { 
    JFrame f = new JFrame("BasicDnD"); 
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    f.setContentPane(new BasicDnD().makeUI()); 
    f.setSize(320, 320); 
    f.setLocationRelativeTo(null); 
    f.setVisible(true); 
    } 
    public static void main(String[] args) { 
    EventQueue.invokeLater(new Runnable() { 
     @Override public void run() { createAndShowGUI(); } 
    }); 
    } 
}