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增强的拖放功能
在Java SE 6中的拖放功能得到了增强，这主要表现在两个方面。
·可以定制拖放模式。
可以在拖放的过程中加入其它的辅助信息。 首先需要通过JList、JTable等控件的setDropMode()方法来设置一个拖动模式。所有的控件都可以使用USER_SELECTION模式。这个模式在以前的Java SE版本中就有。这也是默认的拖放模式。
JList、JTable和Jlist都支持ON模式，这个模式允许你将对象拖到其它项的上方。而INSERT模式允许将一个对象插入在其它项之间。而ON_OR_INSERT模式是前3种模式的组合。下面的代码将演示一个拖动的例子。
import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import javax.swing.tree.*;
public class TestDrapDrop
{
public static void main(String args[])
{
JFrame f = new JFrame("拖放测试");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel top = new JPanel(new BorderLayout());
JLabel dragLabel = new JLabel("拖我:");
JTextField text = new JTextField();
text.setDragEnabled(true);
top.add(dragLabel, BorderLayout.WEST);
top.add(text, BorderLayout.CENTER);
f.add(top, BorderLayout.NORTH);
final JTree tree = new JTree();
final DefaultTreeModel model = (DefaultTreeModel) tree.getModel();
tree.setTransferHandler(new TransferHandler()
{
public boolean canImport(TransferHandler.TransferSupport support)
{
if (!support.isDataFlavorSupported(DataFlavor.stringFlavor) || !support.isDrop())
{
return false;
}
JTree.DropLocation dropLocation = (JTree.DropLocation) suppor.getDropLocation();
return dropLocation.getPath() != null;
}
public boolean importData(TransferHandler.TransferSupport support)
{
if (!canImport(support))
{
return false;
}
JTree.DropLocation dropLocation = (JTree.DropLocation) support.getDropLocation();
TreePath path = dropLocation.getPath();
Transferable transferable = support.getTransferable();
String transferData;
try
{
transferData = (String) transferable .getTransferData(DataFlavor.stringFlavor);
}
catch (IOException e)
{
return false;
}
catch (UnsupportedFlavorException e)
{
return false;
}
int childIndex = dropLocation.getChildIndex();
if (childIndex == -1)
{
childIndex = model.getChildCount(path.getLastPathComponent());
}
DefaultMutableTreeNode newNode = new DefaultMutableTreeNode( transferData);
DefaultMutableTreeNode parentNode = (DefaultMutableTreeNode) path.getLastPathComponent();
model.insertNodeInto(newNode, parentNode, childIndex);
TreePath newPath = path.pathByAddingChild(newNode);
tree.makeVisible(newPath);
tree.scrollRectToVisible(tree.getPathBounds(newPath));
return true;
}
});
JScrollPane pane = new JScrollPane(tree);
f.add(pane, BorderLayout.CENTER);
JPanel bottom = new JPanel();
JLabel comboLabel = new JLabel("DropMode");
String options[] ={ "USE_SELECTION", "ON", "INSERT", "ON_OR_INSERT" };
final DropMode mode[] =
{DropMode.USE_SELECTION, DropMode.ON, DropMode.INSERT, DropMode.ON_OR_INSERT };
final JComboBox combo = new JComboBox(options);
combo.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
int selectedIndex = combo.getSelectedIndex();
tree.setDropMode(mode[selectedIndex]);
}
});
bottom.add(comboLabel);
bottom.add(combo);
f.add(bottom, BorderLayout.SOUTH);
f.setSize(300, 400);
f.setVisible(true);
} |
图9为拖动程序的运行界面。在上面的文本框里输入相应的文本，然后将其选择再拖动到下方的树中。
 图9 拖动界面 |
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