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How to Write a Tree Model Listener

By implementing a tree model listener, you can detect when the data displayed by a tree changes. You might use a tree model listener to detect when the user edits tree nodes. To see an example and discussion of doing so, read Dynamically Changing a Tree.

The Tree Model Event API

The TreeModelListener interface contains four methods:

void treeNodesChanged(TreeModelEvent)

Called when one or more sibling nodes have changed in some way.

void treeNodesInserted(TreeModelEvent)

Called after nodes have been inserted into the tree.

void treeNodesRemoved(TreeModelEvent)

Called after nodes have been removed from the tree.

void treeNodesStructureChanged(TreeModelEvent)

Called after the tree's structure has drastically changed.

Each tree model event method has a single parameter: a TreeModelEvent object. The TreeModelEvent class defines the following useful method:

int[] getChildIndices()

For treeNodesChanged, treeNodesInserted, and treeNodesRemoved, returns the indices of the changed, inserted, or deleted nodes, respectively. Returns nothing useful for treeStructureChanged.

Object[] getChildren()

Returns the objects corresponding to the child indices.

Object[] getPath()

Returns the path to the parent of the changed, inserted, or deleted nodes. For treeStructureChanged, returns the path to the node beneath which the structure has changed.

TreePath getTreePath()

Returns the same thing as getPath, but as a TreePath object.

Also useful is the getSource method, which TreeModelEvent inherits from EventObject.

The DynamicTree example implements a tree model listener to detect when the user has edited a node's data. You can find the listener's code in DynamicTree. The example also relies on DynamicTreeDemo. The code is discussed in Dynamically Changing a Tree.

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