The TreeView control provides a view on to a tree root (of type
TreeItem). By using a TreeView, it is possible to drill down into the
children of a TreeItem, recursively until a TreeItem has no children (that is,
it is a leaf node in the tree). To facilitate this, unlike controls
like ListView, in TreeView it is necessary to only
specify the root node.
For more information on building up a tree using this approach, refer to the
TreeItem class documentation. Briefly however, to create a TreeView,
you should do something along the lines of the following:
TreeItem<String> root = new TreeItem<String>("Root Node");
root.setExpanded(true);
root.getChildren().addAll(
new TreeItem<String>("Item 1"),
new TreeItem<String>("Item 2"),
new TreeItem<String>("Item 3")
);
TreeView<String> treeView = new TreeView<String>(root);
A TreeView may be configured to optionally hide the root node by setting the
showRoot property to false. If the root
node is hidden, there is one less level of indentation, and all children
nodes of the root node are shown. By default, the root node is shown in the
TreeView.
To track selection and focus, it is necessary to become familiar with the
SelectionModel and FocusModel classes. A TreeView has at most
one instance of each of these classes, available from
selectionModel and
focusModel properties respectively.
Whilst it is possible to use this API to set a new selection model, in
most circumstances this is not necessary - the default selection and focus
models should work in most circumstances.
The default SelectionModel used when instantiating a TreeView is
an implementation of the MultipleSelectionModel abstract class.
However, as noted in the API documentation for
the selectionMode
property, the default value is SelectionMode.SINGLE. To enable
multiple selection in a default TreeView instance, it is therefore necessary
to do the following:
treeView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
The visuals of the TreeView can be entirely customized by replacing the
default cell factory. A cell factory is used to
generate TreeCell instances, which are used to represent an item in the
TreeView. See the Cell class documentation for a more complete
description of how to write custom Cells.
This control supports inline editing of values, and this section attempts to give an overview of the available APIs and how you should use them.
Firstly, cell editing most commonly requires a different user interface
than when a cell is not being edited. This is the responsibility of the
Cell implementation being used. For TreeView, this is the responsibility
of the cell factory. It is your choice whether the cell is
permanently in an editing state (e.g. this is common for CheckBox cells),
or to switch to a different UI when editing begins (e.g. when a double-click
is received on a cell).
To know when editing has been requested on a cell,
simply override the javafx.scene.control.Cell.startEdit() method, and
update the cell text and
graphic properties as
appropriate (e.g. set the text to null and set the graphic to be a
TextField). Additionally, you should also override
Cell.cancelEdit() to reset the UI back to its original visual state
when the editing concludes. In both cases it is important that you also
ensure that you call the super method to have the cell perform all duties it
must do to enter or exit its editing mode.
Once your cell is in an editing state, the next thing you are most probably
interested in is how to commit or cancel the editing that is taking place. This is your
responsibility as the cell factory provider. Your cell implementation will know
when the editing is over, based on the user input (e.g. when the user presses
the Enter or ESC keys on their keyboard). When this happens, it is your
responsibility to call Cell.commitEdit(Object) or
Cell.cancelEdit(), as appropriate.
When you call Cell.commitEdit(Object) an event is fired to the
TreeView, which you can observe by adding an EventHandler via
TreeView.setOnEditCommit(javafx.event.EventHandler). Similarly,
you can also observe edit events for
edit start
and edit cancel.
By default the TreeView edit commit handler is non-null, with a default
handler that attempts to overwrite the property value for the
item in the currently-being-edited row. It is able to do this as the
Cell.commitEdit(Object) method is passed in the new value, and this
is passed along to the edit commit handler via the
EditEvent that is fired. It is simply a matter of calling
EditEvent.getNewValue() to retrieve this value.
It is very important to note that if you call
TreeView.setOnEditCommit(javafx.event.EventHandler) with your own
EventHandler, then you will be removing the default handler. Unless
you then handle the writeback to the property (or the relevant data source),
nothing will happen. You can work around this by using the
TreeView.addEventHandler(javafx.event.EventType, javafx.event.EventHandler)
method to add a TreeView.editCommitEvent() EventType with
your desired EventHandler as the second argument. Using this method,
you will not replace the default implementation, but you will be notified when
an edit commit has occurred.
Hopefully this summary answers some of the commonly asked questions. Fortunately, JavaFX ships with a number of pre-built cell factories that handle all the editing requirements on your behalf. You can find these pre-built cell factories in the javafx.scene.control.cell package.
extends
<T> | The type of the item contained within the TreeItem value
property for all tree items in this TreeView. |