TreeView

Perfect! Let’s study TreeView in JavaFX. I’ll give both Java code and FXML version for you.

1️⃣ What is TreeView?

• TreeView is a hierarchical control to display nested items.
• Each item is a TreeItem.
• Commonly used for file explorers, folder structures, or categories.
• Unlike TreeTableView, it doesn’t have columns, only a single tree of nodes.

2️⃣ Key Features

1. Root and children: Use TreeItem to create hierarchy.
2. Selectable: Use getSelectionModel() to get selected items.
3. Expandable/collapsible nodes: Nodes can be expanded or collapsed.
4. Editable: Can edit the text of nodes (optional).

3️⃣ Java Example

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class TreeViewExample extends Application {

    @Override
    public void start(Stage primaryStage) {
        // Root node
        TreeItem<String> root = new TreeItem<>("Root Folder");
        root.setExpanded(true);

        // Child nodes
        TreeItem<String> child1 = new TreeItem<>("File1.txt");
        TreeItem<String> child2 = new TreeItem<>("SubFolder");
        TreeItem<String> child2File = new TreeItem<>("File2.txt");
        child2.getChildren().add(child2File);

        root.getChildren().addAll(child1, child2);

        // TreeView
        TreeView<String> treeView = new TreeView<>(root);

        VBox rootBox = new VBox(treeView);
        rootBox.setStyle("-fx-padding: 20;");

        Scene scene = new Scene(rootBox, 300, 250);
        primaryStage.setScene(scene);
        primaryStage.setTitle("TreeView Example");
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

✅ Explanation:

• TreeItem<String> – each node holds a String.
• root.setExpanded(true) – root node is expanded by default.
• Children are added with getChildren().add(...).

4️⃣ FXML Version

tree_view.fxml

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.TreeView?>
<?import javafx.scene.layout.VBox?>

<VBox xmlns="http://javafx.com/javafx/17.0.2"
      xmlns:fx="http://javafx.com/fxml"
      fx:controller="com.example.TreeViewController"
      spacing="10" style="-fx-padding: 20;">

    <TreeView fx:id="treeView"/>
    
</VBox>

TreeViewController.java

package com.example;

import javafx.fxml.FXML;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;

public class TreeViewController {

    @FXML
    private TreeView<String> treeView;

    @FXML
    public void initialize() {
        // Root node
        TreeItem<String> root = new TreeItem<>("Root Folder");
        root.setExpanded(true);

        // Child nodes
        TreeItem<String> child1 = new TreeItem<>("File1.txt");
        TreeItem<String> child2 = new TreeItem<>("SubFolder");
        TreeItem<String> child2File = new TreeItem<>("File2.txt");
        child2.getChildren().add(child2File);

        root.getChildren().addAll(child1, child2);

        treeView.setRoot(root);
    }
}

5️⃣ Notes

• Selection:

treeView.getSelectionModel().selectedItemProperty().addListener((obs, oldVal, newVal) -> {
    System.out.println("Selected: " + newVal.getValue());
});

• Editable nodes:

treeView.setEditable(true);

• Icons: You can add setGraphic(Node) for icons next to text.