Java Reference
In-Depth Information
JComboBox comboBox = new JComboBox(args);
TreeCellEditor comboEditor = new DefaultCellEditor(comboBox);
TreeCellEditor editor = new DefaultTreeCellEditor(tree, renderer, comboEditor);
...
}
Creating a Proper ComboBox Editor for a Tree
As Figure 17-13 showed, using a
JComboBox
as the
TreeCellEditor
via a
DefaultCellEditor
doesn't place the appropriate node-type icon next to the editor. If you want the icons present,
you need to combine the
DefaultCellEditor
with a
DefaultTreeCellEditor
to get an editor
with both an icon and an editor. It's really not as hard as it sounds. It just involves two extra
steps: getting the renderer for the tree (from which to get the icons), and then combining the
icon with the editor to get a new editor. The following source demonstrates this:
JTree tree = new JTree();
tree.setEditable(true);
DefaultTreeCellRenderer renderer = (DefaultTreeCellRenderer)tree.getCellRenderer();
String elements[] = { "Root", "chartreuse", "rugby", "sushi"} ;
JComboBox comboBox = new JComboBox(elements);
comboBox.setEditable(true);
TreeCellEditor comboEditor = new DefaultCellEditor(comboBox);
TreeCellEditor editor = new DefaultTreeCellEditor(tree, renderer, comboEditor);
tree.setCellEditor(editor);
The improved output is shown in Figure 17-15.
Figure 17-15.
An editable JTree with a JComboBox editor and tree icons
Creating an Editor Just for Leaf Nodes
In some cases, you will want only the leaf nodes of a tree to be editable. Returning
null
from the
getTreeCellEditorComponent()
request effectively makes a node not editable. Unfortunately,
this causes a
NullPointerException
to be thrown by the user interface class.
Instead of returning
null
, you can override the default behavior of the
public boolean
isCellEditable(EventObject object)
method, which is part of the
CellEditor
interface. If the
original return value is
true
, you can do an additional check to see if the selected node of the
tree is a leaf. Nodes of a tree implement the
TreeNode
interface (described later in this chapter
in the “TreeNode Interface” section ). This interface happens to have the method
public
