Thread: JTree DnD Problem

I've implemented drag and drop functionality in my JTree so I can reorder the nodes. I also have two methods for adding nodes; one is with a button, and another is a context menu that is triggered by the node. Button method works fine, but once I add a node with the context menu, drag and drop starts malfunctioning (nodes start dissapearing, arrayindexoutofbounds exceptions..). I don't understand why its doing this because both codes are pretty much the same.

DnDProblem.java (main)

package dndproblem;
 
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
 
public class DnDProblem extends JFrame{
 
	private DnDJTree tree;
	private JButton addButton;
 
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			@Override
			public void run() {
				DnDProblem dndprb = new DnDProblem();
			}
		});
	}
 
	public DnDProblem() {
		setSize(300, 400);
		setLocationRelativeTo(null);
		setDefaultCloseOperation(EXIT_ON_CLOSE);
		setLayout(new BorderLayout());
 
		tree = new DnDJTree();
		add(tree, BorderLayout.CENTER);
 
		addButton = new JButton("Add");
		addButton.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				((DefaultTreeModel)tree.getModel()).insertNodeInto(new DefaultMutableTreeNode(new NodeData("New Node")),
																   (DefaultMutableTreeNode)tree.getModel().getRoot(),
																   0);
			}
		});
		add(addButton, BorderLayout.SOUTH);
 
 
		setVisible(true);
	}
}

DnDJTree.java

package dndproblem;
 
import javax.swing.DropMode;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
 
public class DnDJTree extends JTree{
	public DnDJTree() {
		setDragEnabled(true);
		setDropMode(DropMode.ON_OR_INSERT);
		setTransferHandler(new DnDTransferHandler());
 
		DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
		root.add(new DefaultMutableTreeNode(new NodeData("Child 1")));
		root.add(new DefaultMutableTreeNode(new NodeData("Child 2")));
		root.add(new DefaultMutableTreeNode(new NodeData("Child 3")));
		root.add(new DefaultMutableTreeNode(new NodeData("Child 4")));
 
		setModel(new DefaultTreeModel(root));
		addMouseListener(new MouseMenuAdapter());
 
		Common.tree = this;
	}
}

DnDTransferHandler.java

package dndproblem;
 
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import javax.swing.JComponent;
import javax.swing.JTree;
import javax.swing.TransferHandler;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
 
 
public class DnDTransferHandler extends TransferHandler{
 
	public static final DataFlavor NODE_FLAVOR = new DataFlavor(PackedNode.class, "Node Flavor");
 
	public DnDTransferHandler() {
		super();
	}
 
	@Override
	public int getSourceActions(JComponent c) {
		return MOVE;
	}
 
	@Override
	public boolean canImport(TransferSupport support) {
		try {
			//get the nodes involved in the move
			DefaultTreeModel model = (DefaultTreeModel) ((JTree)support.getComponent()).getModel();
			JTree.DropLocation dloc = (JTree.DropLocation) support.getDropLocation();
			DefaultMutableTreeNode child = (DefaultMutableTreeNode) support.getTransferable().getTransferData(NODE_FLAVOR);
			DefaultMutableTreeNode parent = (DefaultMutableTreeNode) dloc.getPath().getLastPathComponent();
 
			//I dont want to be able to drag the root node, and the root has no parent, so...
			if(child.getParent() == null) return false;
			//I dont want to be able to drag a node inside itself ...
			if(parent.isNodeAncestor(child)) return false;
		} catch (IOException e) {
 
		} catch (UnsupportedFlavorException e) {
 
		}
 
		return true;
	}
 
	@Override 
	public Transferable createTransferable(JComponent c) {
		DefaultMutableTreeNode node = (DefaultMutableTreeNode)((JTree)c).getLastSelectedPathComponent();
		return new PackedNode(node);
	}
 
	@Override
	public boolean importData(TransferSupport support) {
		if(canImport(support)) {
			try {
				//get the nodes involved in the move
				DefaultTreeModel model = (DefaultTreeModel) ((JTree)support.getComponent()).getModel();
				JTree.DropLocation dloc = (JTree.DropLocation) support.getDropLocation();
				DefaultMutableTreeNode child = (DefaultMutableTreeNode) support.getTransferable().getTransferData(NODE_FLAVOR);
				DefaultMutableTreeNode parent = (DefaultMutableTreeNode) dloc.getPath().getLastPathComponent();
 
				//drop index
				int destIndex = dloc.getChildIndex();
				if(destIndex == -1) destIndex = 0;
 
				//get a deep copy of the node being moved. Then I can delete the node referenced in
				//the Transferable safely
				ByteArrayOutputStream bos = new ByteArrayOutputStream();
				ObjectOutputStream out = new ObjectOutputStream(bos);
				out.writeObject(child);
				out.flush();
				out.close();
				ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(bos.toByteArray()));
				Object obj = in.readObject();
				in.close();
 
				//insert node
				model.insertNodeInto((DefaultMutableTreeNode)obj, parent, destIndex);
			} catch(IOException e) {
				return false;
			} catch(ClassNotFoundException e) {
				return false;
			} catch(UnsupportedFlavorException e) {
				return false;
			}
 
			return true;
		} else {
			return false;
		}
	}
 
	@Override
	public void exportDone(JComponent c, Transferable t, int action) {
		if(action == MOVE) {
			try {
				DefaultTreeModel model = (DefaultTreeModel)((JTree)c).getModel();
				DefaultMutableTreeNode child = (DefaultMutableTreeNode) t.getTransferData(NODE_FLAVOR);
				model.removeNodeFromParent(child);
			} catch(UnsupportedFlavorException e) {
 
			} catch(IOException e) {
 
			}
		}
	}
}

PackedNode.java

package dndproblem;
 
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;
import javax.swing.tree.DefaultMutableTreeNode;
 
public class PackedNode implements Transferable{
 
	private DefaultMutableTreeNode data;
 
	public PackedNode(DefaultMutableTreeNode node) {
		data = node;
	}
 
	@Override
	public DataFlavor[] getTransferDataFlavors() {
		return new DataFlavor[] {DnDTransferHandler.NODE_FLAVOR};
	}
 
	@Override
	public boolean isDataFlavorSupported(DataFlavor flavor) {
		if(flavor == DnDTransferHandler.NODE_FLAVOR) {
			return true;
		} else {
			return false;
		}
	}
 
	@Override
	public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
		if(flavor == DnDTransferHandler.NODE_FLAVOR) {
			return data;
		} else {
			throw new UnsupportedFlavorException(flavor);
		}
	}
 
}

NodeData.java

package dndproblem;
 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.Serializable;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.JPopupMenu;
import javax.swing.JTextField;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
 
public class NodeData implements   ActionListener,
								   Serializable{
	private String name;
 
	private JPopupMenu context;
	private JMenuItem newNode;
 
	public NodeData(String n) {
		name = n;
 
		//setup context menu for this data type
		context = new JPopupMenu();
		newNode = new JMenuItem("New folder");
		newNode.addActionListener(this);
		context.add(newNode);
	}
 
	public void showMenu(int x, int y) {
		context.show(Common.tree, x, y);
	}
 
	@Override
	public String toString() {
		return name;
	}
 
	@Override
	public void actionPerformed(ActionEvent e) {
		if(e.getSource() == newNode) {
			JTextField tf = new JTextField();
			String n = JOptionPane.showInputDialog(tf, "Folder name:", "New Folder", JOptionPane.PLAIN_MESSAGE);
 
			((DefaultTreeModel)Common.tree.getModel()).insertNodeInto(new DefaultMutableTreeNode(new NodeData(n)),
																   (DefaultMutableTreeNode)Common.tree.getModel().getRoot(),
																   0);
		}
	}
}

MouseMenuAdapter.java

package dndproblem;
 
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;
 
public class MouseMenuAdapter extends MouseAdapter{
	@Override
	public void mousePressed(MouseEvent event) {
		if(event.getButton() == 3) {
			int x = event.getX();																	//get mouse cooridnates
			int y = event.getY();
			JTree tree = (JTree) event.getSource();													//get the tree that was clicked
			TreePath path = tree.getPathForLocation(x, y);											//get a path to the clicked node
 
			if(path == null) return;																//if we missed, return
 
			tree.setSelectionPath(path);															//set the selected node to the one we clicked
			DefaultMutableTreeNode node = (DefaultMutableTreeNode) path.getLastPathComponent();		//get the node we clicked
			Object data = node.getUserObject();														//get the data object from node
 
			if(data instanceof NodeData) ((NodeData)data).showMenu(x, y);							//show the context menu
		}
	}
}

Common.java

package dndproblem;
 
import javax.swing.JTree;
 
public class Common {
	public static JTree tree;
}

Ok, an update to this problem. The problem occurs right after opening a popup menu. If I so much as open then close a popup menu, DnD starts malfunctioning....

I've found a solution that seems to have solved it. It is caused by the JPopupmenu...existing? If I set the menu to null when it is cancelled or will become invisible, then everything works fine. I just re-instantiate it before showing it again.

Sounds like a bug, I dunno. But at least its working now.