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Using JTree and CellRenderers...

Posted on 1998-08-27
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Last Modified: 2012-05-05
I am using a JTree component and I have my own custom TreeCellRenderer:

import com.sun.java.swing.tree.*;
import java.awt.*;
import com.sun.java.swing.*;

public class MyTreeCellRenderer extends Object implements TreeCellRenderer
{
    public MyTreeCellRenderer()
    {
        super();
    }
   
    public Component getTreeCellRendererComponent(JTree tree, Object value,
                         boolean selected, boolean expanded,
                         boolean leaf, int row, boolean hasFocus)
    {
        m_node.setFont(tree.getFont());
        m_node.setBackground(tree.getBackground());
        m_node.setText(value.toString());
       
        return m_node;
    }
   
    private JCheckBox   m_node = new JCheckBox();
}

Whenever I click on a node in the tree, I want to be able to get the JCheckBox object (which is the node that was clicked), so that I can set it to be selected or not selected.  How can I do this?
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Question by:beemer
  • 3
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5 Comments
 
LVL 3

Accepted Solution

by:
sailwind earned 100 total points
ID: 1222663
For your tree component you should have an treeSelectionListener that
watches for the tree events. In the listener (preferrably the tree itself),
define the valueChanged as follows:

Let's say we have a JTree tree.

          public void valueChanged(TreeSelectionEvent e)
          {
              Object pathObj;
              
              // get selected item
   try {
     pathObj = tree.getSelectionPath().getLastPathComponent();
   } catch (NullPointerException ne) {return;}
}

The pathObj is the object that you're trying to get.
0
 

Author Comment

by:beemer
ID: 1222664
How can I do this for a JList?
0
 

Author Comment

by:beemer
ID: 1222665
I tried your idea, and it did not work.

public void valueChanged(TreeSelectionEvent e)
      {
          Object pathObj;
            try
            {
                  pathObj = tree.getSelectionPath().getLastPathComponent();
                  if (pathObj instanceof JCheckBox)
                  {
                        System.out.println("is a JCheckBox");
                  }
            } catch (NullPointerException ne) {return;}
      }

It never printed out that it is a JCheckBox.

Here is my renderer class:

import com.sun.java.swing.tree.*;
import java.awt.*;
import com.sun.java.swing.*;

public class MyTreeCellRenderer extends Object implements TreeCellRenderer
{
    public MyTreeCellRenderer(TreeFrame frame)
    {
        super();
        this.frame = frame;
    }
   
    public Component getTreeCellRendererComponent(JTree tree, Object value,
                         boolean selected, boolean expanded,
                         boolean leaf, int row, boolean hasFocus)
    {
        m_node.setFont(tree.getFont());
        m_node.setBackground(tree.getBackground());
        m_node.setText(value.toString());
       
        return m_node;
    }
   
    private JCheckBox   m_node = new JCheckBox();
    private TreeFrame   frame;
}
0
 
LVL 3

Expert Comment

by:sailwind
ID: 1222666
1. Did you ever register the class as a listener? Namely, you need to invoke:
    tree.addTreeSelectionListener(this);  // where 'this' is the listener

2. If it's not giving you a checkbox object back, do a
    System.out.println(pathObj) to see what type of object it's returning to you.

You can get the current selected List item by invoking:

list.getSelectedValue();
0
 

Author Comment

by:beemer
ID: 1222667
When I do a System.out.println(pathObj), it is just the String text of the JCheckBox
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