JavaFX TreeView

小咪咪 2023-10-15 16:44 8阅读 0赞

The JavaFX *TreeeView* enables you to display tree views inside your JavaFX applications. The JavaFX TreeView is represented by the class `javafx.scene.control.TreeView` . Here is a screenshot of a *JavaFX* *TreeView*:

![7c2de9ccfdb44d10a816d45d5d5991b9.png][]

### Create a TreeView ###

You create a JavaFX `TreeView` simply by creating a new instance of the `TreeView` class. Here is an example of creating a new JavaFX `TreeView` instance:

TreeView treeView = new TreeView();

### Add TreeView to Scene Graph ###

To make a JavaFX `TreeView` visible it must be added to the [JavaFX scene graph][]. Here is an example showing how to add a JavaFX `TreeView` to the JavaFX scene graph:

import javafx.application.Application;
    import javafx.scene.Scene;
    import javafx.scene.control.TreeView;
    import javafx.scene.layout.VBox;
    import javafx.stage.Stage;
    
    public class TreeViewExample extends Application {
    
        public static void main(String[] args) {
            launch(args);
        }
    
        @Override
        public void start(Stage primaryStage) {
            TreeView treeView = new TreeView();
    
            VBox vbox = new VBox(treeView);
    
            Scene scene = new Scene(vbox);
    
            primaryStage.setScene(scene);
    
            primaryStage.show();
        }
    
    }

Notice, that the `TreeView` created in the above example will not have any items (nodes) to display. We will see how to add tree items to a `TreeView` in the next section.

### Add Tree Items to TreeView ###

The items in the tree displayed by a JavaFX `TreeView` are represented by the `TreeItem` class (`javafx.scene.control.TreeItem`). Here is an example of creating a set of `TreeItem` instances and adding them to a JavaFX `TreeView` instance:

TreeItem rootItem = new TreeItem("Tutorials");
    
    TreeItem webItem = new TreeItem("Web Tutorials");
    webItem.getChildren().add(new TreeItem("HTML  Tutorial"));
    webItem.getChildren().add(new TreeItem("HTML5 Tutorial"));
    webItem.getChildren().add(new TreeItem("CSS Tutorial"));
    webItem.getChildren().add(new TreeItem("SVG Tutorial"));
    rootItem.getChildren().add(webItem);
    
    TreeItem javaItem = new TreeItem("Java Tutorials");
    javaItem.getChildren().add(new TreeItem("Java Language"));
    javaItem.getChildren().add(new TreeItem("Java Collections"));
    javaItem.getChildren().add(new TreeItem("Java Concurrency"));
    rootItem.getChildren().add(javaItem);
    
    TreeView treeView = new TreeView();
    treeView.setRoot(rootItem);

### Add Children to a TreeItem ###

If you look at the example in the previous section, you can see that a `TreeItem` can have other `TreeItem` instances as children. This parent-child relationship can continue recursively, indefinitely. This is how you structure the tree nodes logically in your JavaFX application. Here is an example that shows how to add child `TreeItem` instances to a parent `TreeItem`:

TreeItem javaItem = new TreeItem("Java Tutorials");
    javaItem.getChildren().add(new TreeItem("Java Language"));
    javaItem.getChildren().add(new TreeItem("Java Collections"));
    javaItem.getChildren().add(new TreeItem("Java Concurrency"));
    
    TreeItem rootItem = new TreeItem("Tutorials");
    rootItem.getChildren().add(javaItem);

This example creates a tree with a single root `TreeItem` which has one child `TreeItem` set on it, and this child `TreeItem` has itself 3 child `TreeItem` instances added to it.

### Hide Root Item of TreeView ###

You can hide the root item (root node) of a JavaFX `TreeView`. You do so by calling the `setShowRoot()` method, passing the `boolean` value `false` to it as parameter. Here is an example of hiding the root `TreeItem` of a JavaFX `TreeView`:

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 {
    
        public static void main(String[] args) {
            launch(args);
        }
    
        @Override
        public void start(Stage primaryStage) {
    
            TreeItem rootItem = new TreeItem("Tutorials");
    
            TreeItem webItem = new TreeItem("Web Tutorials");
            webItem.getChildren().add(new TreeItem("HTML  Tutorial"));
            webItem.getChildren().add(new TreeItem("HTML5 Tutorial"));
            webItem.getChildren().add(new TreeItem("CSS Tutorial"));
            webItem.getChildren().add(new TreeItem("SVG Tutorial"));
            rootItem.getChildren().add(webItem);
    
            TreeItem javaItem = new TreeItem("Java Tutorials");
            javaItem.getChildren().add(new TreeItem("Java Language"));
            javaItem.getChildren().add(new TreeItem("Java Collections"));
            javaItem.getChildren().add(new TreeItem("Java Concurrency"));
            rootItem.getChildren().add(javaItem);
    
            TreeView treeView = new TreeView();
            treeView.setRoot(rootItem);
    
            treeView.setShowRoot(false);
    
            VBox vbox = new VBox(treeView);
            Scene scene = new Scene(vbox);
            primaryStage.setScene(scene);
            primaryStage.show();
        }
    
    }

Notice the line in bold. That is the line that instructs the JavaFX `TreeView` to hide the root node. Here is a screenshot showing how the resulting JavaFX `TreeView` looks, with all nodes expanded:

![386957fe44534daa91f07cd8a6ba3cd0.png][]

Notice how the root `TreeItem` with the text `Tutorials` is not displayed.

[7c2de9ccfdb44d10a816d45d5d5991b9.png]: https://img-blog.csdnimg.cn/7c2de9ccfdb44d10a816d45d5d5991b9.png
[JavaFX scene graph]: https://jenkov.com/tutorials/javafx/scene.html#the-scene-graph
[386957fe44534daa91f07cd8a6ba3cd0.png]: https://img-blog.csdnimg.cn/386957fe44534daa91f07cd8a6ba3cd0.png