TreeItem (JavaFX 17)

Module javafx.controls
Package javafx.scene.control

## Class TreeItem<T>

- java.lang.Object
- - javafx.scene.control.TreeItem<T>

- Type Parameters:
    `T` - The type of the `value` property within TreeItem.
  All Implemented Interfaces:
    `EventTarget`
  Direct Known Subclasses:
    `CheckBoxTreeItem`

      public class TreeItem<T>
      extends Object
      implements EventTarget

  The model for a single node supplying a hierarchy of values to a control such as `TreeView`. The model may be implemented such that values may be loaded in memory as they are needed.

  The model allows registration of listeners which will be notified as the number of items changes, their position or if the values themselves change. Note however that a TreeItem is not a Node, and therefore no visual events will be fired on the TreeItem. To get these events, it is necessary to add relevant observers to the TreeCell instances (via a custom cell factory - see the `Cell` class documentation for more details).

  In the simplest case, TreeItem instances may be created in memory as such:

       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);

  This approach works well for simple tree structures, or when the data is not excessive (so that it can easily fit in memory). In situations where the size of the tree structure is unknown (and therefore potentially huge), there is the option of creating TreeItem instances on-demand in a memory-efficient way. To demonstrate this, the code below creates a file system browser:

        private TreeView buildFileSystemBrowser() {
            TreeItem<File> root = createNode(new File("/"));
            return new TreeView<File>(root);
        }

        // This method creates a TreeItem to represent the given File. It does this
        // by overriding the TreeItem.getChildren() and TreeItem.isLeaf() methods
        // anonymously, but this could be better abstracted by creating a
        // 'FileTreeItem' subclass of TreeItem. However, this is left as an exercise
        // for the reader.
        private TreeItem<File> createNode(final File f) {
            return new TreeItem<File>(f) {
                // We cache whether the File is a leaf or not. A File is a leaf if
                // it is not a directory and does not have any files contained within
                // it. We cache this as isLeaf() is called often, and doing the
                // actual check on File is expensive.
                private boolean isLeaf;

                // We do the children and leaf testing only once, and then set these
                // booleans to false so that we do not check again during this
                // run. A more complete implementation may need to handle more
                // dynamic file system situations (such as where a folder has files
                // added after the TreeView is shown). Again, this is left as an
                // exercise for the reader.
                private boolean isFirstTimeChildren = true;
                private boolean isFirstTimeLeaf = true;

                @Override public ObservableList<TreeItem<File>> getChildren() {
                    if (isFirstTimeChildren) {
                        isFirstTimeChildren = false;

                        // First getChildren() call, so we actually go off and
                        // determine the children of the File contained in this TreeItem.
                        super.getChildren().setAll(buildChildren(this));
                    }
                    return super.getChildren();
                }

                @Override public boolean isLeaf() {
                    if (isFirstTimeLeaf) {
                        isFirstTimeLeaf = false;
                        File f = (File) getValue();
                        isLeaf = f.isFile();
                    }

                    return isLeaf;
                }

                private ObservableList<TreeItem<File>> buildChildren(TreeItem<File> TreeItem) {
                    File f = TreeItem.getValue();
                    if (f != null && f.isDirectory()) {
                        File[] files = f.listFiles();
                        if (files != null) {
                            ObservableList<TreeItem<File>> children = FXCollections.observableArrayList();

                            for (File childFile : files) {
                                children.add(createNode(childFile));
                            }

                            return children;
                        }
                    }

                    return FXCollections.emptyObservableList();
                }
            };
        }

  TreeItem Events

  TreeItem supports the same event bubbling concept as elsewhere in the scenegraph. This means that it is not necessary to listen for events on all TreeItems (and this is certainly not encouraged!). A better, and far more low cost solution is to instead attach event listeners to the TreeView `root` item. As long as there is a path between where the event occurs and the root TreeItem, the event will be bubbled to the root item.

  It is important to note however that a TreeItem is not a Node, which means that only the event types defined in TreeItem will be delivered. To listen to general events (for example mouse interactions), it is necessary to add the necessary listeners to the `cells` contained within the TreeView (by providing a `cell factory`).

  The TreeItem class defines a number of events, with a defined hierarchy. These are shown below (follow the links to learn more about each event type):

  - `TreeItem.treeNotificationEvent()`
    - `TreeItem.valueChangedEvent()`
    - `TreeItem.graphicChangedEvent()`
    - `TreeItem.expandedItemCountChangeEvent()`
      - `TreeItem.branchExpandedEvent()`
      - `TreeItem.branchCollapsedEvent()`
      - `TreeItem.childrenModificationEvent()`

  The indentation shown above signifies the relationship between event types. For example, all TreeItem event types have `treeNotificationEvent()` as their parent event type, and the branch `expand` / `collapse` event types are both `treeNotificationEvent()`. For performance reasons, it is encouraged to listen to only the events you need to listen to. This means that it is encouraged that it is better to listen to, for example, `TreeItem.valueChangedEvent()`, rather than `TreeItem.treeNotificationEvent()`.

  Since:
    JavaFX 2.0
  See Also:
    `TreeView`

- - ### Property Summary

    Properties
    Type | Property | Description
    --- | --- | ---
    `BooleanProperty` | `expanded` | The expanded state of this TreeItem.
    `ObjectProperty<Node>` | `graphic` | The node that is generally shown to the left of the value property.
    `ReadOnlyBooleanProperty` | `leaf` | Represents the TreeItem leaf property, which is true if the TreeItem has no children.
    `ReadOnlyObjectProperty<TreeItem<T>>` | `parent` | A property that represents the parent of this TreeItem.
    `ObjectProperty<T>` | `value` | A property representing the application-specific data contained within this TreeItem.

  - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class | Description
    --- | --- | ---
    `static class` | `TreeItem.TreeModificationEvent<T>` | An `Event` that contains relevant information for all forms of TreeItem modifications.

  - ### Constructor Summary

    Constructors
    Constructor | Description
    --- | ---
    `TreeItem()` | Creates an empty TreeItem.
    `TreeItem​(T value)` | Creates a TreeItem with the value property set to the provided object.
    `TreeItem​(T value, Node graphic)` | Creates a TreeItem with the value property set to the provided object, and the graphic set to the provided Node.

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `<E extends Event> void` | `addEventHandler​(EventType<E> eventType, EventHandler<E> eventHandler)` | Registers an event handler to this TreeItem.
    `static <T> EventType<TreeItem.TreeModificationEvent<T>>` | `branchCollapsedEvent()` | An EventType used when the TreeItem receives a modification to its expanded property, such that the TreeItem is now in the collapsed state.
    `static <T> EventType<TreeItem.TreeModificationEvent<T>>` | `branchExpandedEvent()` | An EventType used when the TreeItem receives a modification to its expanded property, such that the TreeItem is now in the expanded state.
    `static <T> EventType<TreeItem.TreeModificationEvent<T>>` | `childrenModificationEvent()` | An EventType used when the TreeItem receives a direct modification to its children list.
    `static <T> EventType<TreeItem.TreeModificationEvent<T>>` | `expandedItemCountChangeEvent()` | The general EventType used when the TreeItem receives a modification that results in the number of children being visible changes.
    `BooleanProperty` | `expandedProperty()` | The expanded state of this TreeItem.
    `ObservableList<TreeItem<T>>` | `getChildren()` | The children of this TreeItem.
    `Node` | `getGraphic()` | Returns the node that is generally shown to the left of the value property.
    `TreeItem<T>` | `getParent()` | The parent of this TreeItem.
    `T` | `getValue()` | Returns the application-specific data represented by this TreeItem.
    `static <T> EventType<TreeItem.TreeModificationEvent<T>>` | `graphicChangedEvent()` | An EventType used when the TreeItem receives a modification to its graphic property.
    `ObjectProperty<Node>` | `graphicProperty()` | The node that is generally shown to the left of the value property.
    `boolean` | `isExpanded()` | Returns the expanded state of this TreeItem.
    `boolean` | `isLeaf()` | A TreeItem is a leaf if it has no children.
    `ReadOnlyBooleanProperty` | `leafProperty()` | Represents the TreeItem leaf property, which is true if the TreeItem has no children.
    `TreeItem<T>` | `nextSibling()` | Returns the next sibling of the TreeItem.
    `TreeItem<T>` | `nextSibling​(TreeItem<T> afterNode)` | Returns the next sibling after the given node.
    `ReadOnlyObjectProperty<TreeItem<T>>` | `parentProperty()` | A property that represents the parent of this TreeItem.
    `TreeItem<T>` | `previousSibling()` | Returns the previous sibling of the TreeItem.
    `TreeItem<T>` | `previousSibling​(TreeItem<T> beforeNode)` | Returns the previous sibling after the given node.
    `<E extends Event> void` | `removeEventHandler​(EventType<E> eventType, EventHandler<E> eventHandler)` | Unregisters a previously registered event handler from this TreeItem.
    `void` | `setExpanded​(boolean value)` | Sets the expanded state of this TreeItem.
    `void` | `setGraphic​(Node value)` | Sets the node that is generally shown to the left of the value property.
    `void` | `setValue​(T value)` | Sets the application-specific data represented by this TreeItem.
    `String` | `toString()` | Returns a string representation of this `TreeItem` object.
    `static <T> EventType<TreeItem.TreeModificationEvent<T>>` | `treeNotificationEvent()` | The base EventType used to indicate that an event has occurred within a TreeItem.
    `static <T> EventType<TreeItem.TreeModificationEvent<T>>` | `valueChangedEvent()` | An EventType used when the TreeItem receives a modification to its value property.
    `ObjectProperty<T>` | `valueProperty()` | A property representing the application-specific data contained within this TreeItem.

    - ### Methods declared in class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

    - ### Methods declared in interface javafx.event.EventTarget

      `buildEventDispatchChain`

- - ### Property Detail

    - #### value

          public final ObjectProperty<T> valueProperty

      A property representing the application-specific data contained within this TreeItem.
      See Also:
        `getValue()`, `setValue(T)`

    - #### graphic

          public final ObjectProperty<Node> graphicProperty

      The node that is generally shown to the left of the value property. For best effect, this tends to be a 16x16 image.
      See Also:
        `getGraphic()`, `setGraphic(Node)`

    - #### expanded

          public final BooleanProperty expandedProperty

      The expanded state of this TreeItem.
      See Also:
        `isExpanded()`, `setExpanded(boolean)`

    - #### leaf

          public final ReadOnlyBooleanProperty leafProperty

      Represents the TreeItem leaf property, which is true if the TreeItem has no children.
      See Also:
        `isLeaf()`

    - #### parent

          public final ReadOnlyObjectProperty<TreeItem<T>> parentProperty

      A property that represents the parent of this TreeItem.
      See Also:
        `getParent()`

  - ### Constructor Detail

    - #### TreeItem

          public TreeItem()

      Creates an empty TreeItem.

    - #### TreeItem

          public TreeItem​(T value)

      Creates a TreeItem with the value property set to the provided object.
      Parameters:
        `value` - The object to be stored as the value of this TreeItem.

    - #### TreeItem

          public TreeItem​(T value,
                          Node graphic)

      Creates a TreeItem with the value property set to the provided object, and the graphic set to the provided Node.
      Parameters:
        `value` - The object to be stored as the value of this TreeItem.
        `graphic` - The Node to show in the TreeView next to this TreeItem.

  - ### Method Detail

    - #### treeNotificationEvent

          public static <T> EventType<TreeItem.TreeModificationEvent<T>> treeNotificationEvent()

      The base EventType used to indicate that an event has occurred within a TreeItem. When an event occurs in a TreeItem, the event is fired to any listeners on the TreeItem that the event occurs, before it 'bubbles' up the TreeItem chain by following the TreeItem parent property. This repeats until a TreeItem whose parent TreeItem is null is reached At this point the event stops 'bubbling' and goes no further. This means that events that occur on a TreeItem can be relatively cheap, as a listener needs only be installed on the TreeView root node to be alerted of events happening at any point in the tree.
      Type Parameters:
        `T` - The type of the value contained within the TreeItem.
      Returns:
        the base EventType when an event has occurred within a TreeItem

    - #### expandedItemCountChangeEvent

          public static <T> EventType<TreeItem.TreeModificationEvent<T>> expandedItemCountChangeEvent()

      The general EventType used when the TreeItem receives a modification that results in the number of children being visible changes. This is normally achieved via one of the sub-types of this EventType (see `branchExpandedEvent()`, `branchCollapsedEvent()` and `childrenModificationEvent()` for the three sub-types).
      Type Parameters:
        `T` - The type of the value contained within the TreeItem.
      Returns:
        The general EventType when the TreeItem receives a modification
      Since:
        JavaFX 8.0

    - #### branchExpandedEvent

          public static <T> EventType<TreeItem.TreeModificationEvent<T>> branchExpandedEvent()

      An EventType used when the TreeItem receives a modification to its expanded property, such that the TreeItem is now in the expanded state.
      Type Parameters:
        `T` - The type of the value contained within the TreeItem.
      Returns:
        The EventType used when the TreeItem receives a modification

    - #### branchCollapsedEvent

          public static <T> EventType<TreeItem.TreeModificationEvent<T>> branchCollapsedEvent()

      An EventType used when the TreeItem receives a modification to its expanded property, such that the TreeItem is now in the collapsed state.
      Type Parameters:
        `T` - The type of the value contained within the TreeItem.
      Returns:
        The EventType when the TreeItem receives a modification

    - #### childrenModificationEvent

          public static <T> EventType<TreeItem.TreeModificationEvent<T>> childrenModificationEvent()

      An EventType used when the TreeItem receives a direct modification to its children list.
      Type Parameters:
        `T` - The type of the value contained within the TreeItem.
      Returns:
        The EventType when the TreeItem receives a direct modification to its children list

    - #### valueChangedEvent

          public static <T> EventType<TreeItem.TreeModificationEvent<T>> valueChangedEvent()

      An EventType used when the TreeItem receives a modification to its value property.
      Type Parameters:
        `T` - The type of the value contained within the TreeItem.
      Returns:
        The EventType when the TreeItem receives a modification to its value property

    - #### graphicChangedEvent

          public static <T> EventType<TreeItem.TreeModificationEvent<T>> graphicChangedEvent()

      An EventType used when the TreeItem receives a modification to its graphic property.
      Type Parameters:
        `T` - The type of the value contained within the TreeItem.
      Returns:
        The EventType when the TreeItem receives a modification to its graphic property

    - #### setValue

          public final void setValue​(T value)

      Sets the application-specific data represented by this TreeItem.
      Parameters:
        `value` - the application-specific data

    - #### getValue

          public final T getValue()

      Returns the application-specific data represented by this TreeItem.
      Returns:
        the data represented by this TreeItem

    - #### valueProperty

          public final ObjectProperty<T> valueProperty()

      A property representing the application-specific data contained within this TreeItem.
      See Also:
        `getValue()`, `setValue(T)`

    - #### setGraphic

          public final void setGraphic​(Node value)

      Sets the node that is generally shown to the left of the value property. For best effect, this tends to be a 16x16 image.
      Parameters:
        `value` - The graphic node that will be displayed to the user.

    - #### getGraphic

          public final Node getGraphic()

      Returns the node that is generally shown to the left of the value property. For best effect, this tends to be a 16x16 image.
      Returns:
        The graphic node that will be displayed to the user.

    - #### graphicProperty

          public final ObjectProperty<Node> graphicProperty()

      The node that is generally shown to the left of the value property. For best effect, this tends to be a 16x16 image.
      See Also:
        `getGraphic()`, `setGraphic(Node)`

    - #### setExpanded

          public final void setExpanded​(boolean value)

      Sets the expanded state of this TreeItem. This has no effect on a TreeItem with no children. On a TreeItem with children however, the result of toggling this property is that visually the children will either become visible or hidden, based on whether expanded is set to true or false.
      Parameters:
        `value` - If this TreeItem has children, calling setExpanded with `true` will result in the children becoming visible. Calling setExpanded with `false` will hide any children belonging to the TreeItem.

    - #### isExpanded

          public final boolean isExpanded()

      Returns the expanded state of this TreeItem.
      Returns:
        Returns the expanded state of this TreeItem.

    - #### expandedProperty

          public final BooleanProperty expandedProperty()

      The expanded state of this TreeItem.
      See Also:
        `isExpanded()`, `setExpanded(boolean)`

    - #### isLeaf

          public boolean isLeaf()

      A TreeItem is a leaf if it has no children. The isLeaf method may of course be overridden by subclasses to support alternate means of defining how a TreeItem may be a leaf, but the general premise is the same: a leaf can not be expanded by the user, and as such will not show a disclosure node or respond to expansion requests.
      Returns:
        true if this TreeItem has no children

    - #### leafProperty

          public final ReadOnlyBooleanProperty leafProperty()

      Represents the TreeItem leaf property, which is true if the TreeItem has no children.
      See Also:
        `isLeaf()`

    - #### getParent

          public final TreeItem<T> getParent()

      The parent of this TreeItem. Each TreeItem can have no more than one parent. If a TreeItem has no parent, it represents a root in the tree model.
      Returns:
        The parent of this TreeItem, or null if the TreeItem has no parent.

    - #### parentProperty

          public final ReadOnlyObjectProperty<TreeItem<T>> parentProperty()

      A property that represents the parent of this TreeItem.
      See Also:
        `getParent()`

    - #### getChildren

          public ObservableList<TreeItem<T>> getChildren()

      The children of this TreeItem. This method is called frequently, and it is therefore recommended that the returned list be cached by any TreeItem implementations.
      Returns:
        a list that contains the child TreeItems belonging to the TreeItem.

    - #### previousSibling

          public TreeItem<T> previousSibling()

      Returns the previous sibling of the TreeItem. Ordering is based on the position of the TreeItem relative to its siblings in the children list belonging to the parent of the TreeItem.
      Returns:
        A TreeItem that is the previous sibling of the current TreeItem, or null if no such sibling can be found.

    - #### previousSibling

          public TreeItem<T> previousSibling​(TreeItem<T> beforeNode)

      Returns the previous sibling after the given node. Ordering is based on the position of the given TreeItem relative to its siblings in the children list belonging to the parent of the TreeItem.
      Parameters:
        `beforeNode` - The TreeItem for which the previous sibling is being sought.
      Returns:
        A TreeItem that is the previous sibling of the given TreeItem, or null if no such sibling can be found.

    - #### nextSibling

          public TreeItem<T> nextSibling()

      Returns the next sibling of the TreeItem. Ordering is based on the position of the TreeItem relative to its siblings in the children list belonging to the parent of the TreeItem.
      Returns:
        A TreeItem that is the next sibling of the current TreeItem, or null if no such sibling can be found.

    - #### nextSibling

          public TreeItem<T> nextSibling​(TreeItem<T> afterNode)

      Returns the next sibling after the given node. Ordering is based on the position of the given TreeItem relative to its siblings in the children list belonging to the parent of the TreeItem.
      Parameters:
        `afterNode` - The TreeItem for which the next sibling is being sought.
      Returns:
        A TreeItem that is the next sibling of the given TreeItem, or null if no such sibling can be found.

    - #### toString

          public String toString()

      Returns a string representation of this `TreeItem` object.
      Overrides:
        `toString` in class `Object`
      Returns:
        a string representation of this `TreeItem` object.

    - #### addEventHandler

          public <E extends Event> void addEventHandler​(EventType<E> eventType,
                                                        EventHandler<E> eventHandler)

      Registers an event handler to this TreeItem. The TreeItem class allows registration of listeners which will be notified as the number of items changes, their position or if the values themselves change. Note however that a TreeItem is not a Node, and therefore no visual events will be fired on the TreeItem. To get these events, it is necessary to add relevant observers to the TreeCell instances (via a custom cell factory - see the `Cell` class documentation for more details).
      Type Parameters:
        `E` - The event
      Parameters:
        `eventType` - the type of the events to receive by the handler
        `eventHandler` - the handler to register
      Throws:
        `NullPointerException` - if the event type or handler is null

    - #### removeEventHandler

          public <E extends Event> void removeEventHandler​(EventType<E> eventType,
                                                           EventHandler<E> eventHandler)

      Unregisters a previously registered event handler from this TreeItem. One handler might have been registered for different event types, so the caller needs to specify the particular event type from which to unregister the handler.
      Type Parameters:
        `E` - The event
      Parameters:
        `eventType` - the event type from which to unregister
        `eventHandler` - the handler to unregister
      Throws:
        `NullPointerException` - if the event type or handler is null