java像BorderPane这样的类在以后进行编码而不是初始化时如何显示更改？

Question

我当时正在研究JavaFX，我意识到了一些让我思考的东西。因此，在我的构造函数中有一个scene，它添加了类型BorderPane的变量root。在主类中，首先调用该类的构造函数，从而初始化场景中的BorderPane。但是，正在名为build的方法中修改和编辑BorderPane。我对BorderPane如何仍然能够从build()显示其更新版本感到困惑，因为在构造函数中它已经被命令显示

这是我的密码：

 public class SnacksOrDrinks
    {
        private BorderPane root;
        private Stage primaryStage;
        private Scene scene;
        private Cart crt;

        public SnacksOrDrinks(Stage primaryStage, Cart crt)
        {
        // BorderPane is being initialised and is being put inside the scene: 
                BorderPane root1 = new BorderPane();        
                this.scene = new Scene(root1, 800, 475);
                this.crt = crt;

            ImageView imgview = new ImageView("./application/MountainPainting.jpg");
            imgview.fitWidthProperty().bind(primaryStage.widthProperty());
            imgview.fitHeightProperty().bind(primaryStage.heightProperty());

            scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
            this.primaryStage = primaryStage;
            this.root = root1;
            root.setStyle("-fx-background-color: blue");


            root.getChildren().add(imgview);
        }

        public void build(Dispenser dis)
        {
            // ItemsPaneProp extends GridPane and stores the common properties shared in other classes.
            ItemsPaneProp pane = new ItemsPaneProp();       

            // Header Created: 
            CommHeaderProp header = new CommHeaderProp("Lopes Vending Machine");


    // However, BorderPane is being modified here, and the constructor has already been called. 
            BorderPane.setAlignment(header, Pos.CENTER);
            root.setTop(header);

            // Create a Line: 
            Line line = new Line(100, 10, 300, 10);
            line.setFill(Color.GOLDENROD);
            line.setStrokeWidth(2);
            line.setSmooth(true);
            pane.add(line, 0, 0);

            // Create all the Scene's Components and setup the Event Handlers
            ImageView img = new ImageView("./application/softdrink.jpg");
            img.setFitWidth(75);
            img.setFitHeight(75);
            Button btn1 = new Button("Select to get Drinks", img);
            btn1.setStyle("-fx-background-color: white");
            btn1.setFont(Font.font("Times New Roman", FontWeight.BOLD, FontPosture.REGULAR, 12));
            btn1.setContentDisplay(ContentDisplay.TOP);
            pane.add(btn1, 0, 1);

            ImageView img1 = new ImageView("./application/potato-chips.png");
            img1.setFitWidth(75);
            img1.setFitHeight(75);
            Button btn2 = new Button("Select to get Snacks", img1);
            btn2.setStyle("-fx-background-color: white");
            btn2.setFont(Font.font("Times New Roman", FontWeight.BOLD, FontPosture.REGULAR, 12));
            btn2.setContentDisplay(ContentDisplay.TOP);`enter code here`
            pane.add(btn2, 1, 1);

            root.setCenter(pane); // The BorderPane is being modified here too, but the constructor isn't updating the scene. Then, how does it still work?

            btn1.setOnMouseClicked(new EventHandler<MouseEvent>()
            {
                @Override
                public void handle(MouseEvent e)
                {
                    // Create, build, and show Scene 2
                    DrinksList scene = new DrinksList(primaryStage, crt);
                    scene.build(dis);
                    scene.show();
                }
            });

            btn2.setOnMouseClicked(new EventHandler<MouseEvent>()
            {
                @Override
                public void handle(MouseEvent e)
                {
                    // Create, build, and show Scene 2
                    SnacksList scene = new SnacksList(primaryStage, crt);
                    scene.build(dis);
                    scene.show();
                }
            });

        }

        public void show()
        {// setting scene:
            primaryStage.setScene(scene);
        }
    }

Answer 1

看看https://docs.oracle.com/javase/8/javafx/scene-graph-tutorial/scenegraph.htm#JFXSG107

The JavaFX scene graph is a retained mode API, meaning that it maintains an internal model of all graphical objects in your application. At any given time, it knows what objects to display, what areas of the screen need repainting, and how to render it all in the most efficient manner.

您的borderPane是SceneGraph的一部分，所以JavaFX知道，当您更改borderPane中的任何内容时，会自动为其调用redraw方法