JavaFX 构造函数和改变场景/阶段

Question

everyone reading

Currently trying to figure out the basics of JavaFX can somebody help me with how to set a new scene using a constructor from another class. I tried the obvious things to attempt but to no avail except for errors being thrown my way. I guess I just do not understand how to change the stage from my main stage to the classes' stage when choosing a specific menu item. I need to figure this out before attempting any of the actual coding for the classes.

Thanks for any help!

Main

    package application;

    import javafx.application.Application;
    import javafx.event.ActionEvent;
    import javafx.event.EventHandler;
    import javafx.scene.Group;
    import javafx.scene.Scene;
    import javafx.scene.control.Button;
    import javafx.scene.control.Label;
    import javafx.scene.control.Menu;
    import javafx.scene.control.MenuBar;
    import javafx.scene.control.MenuItem;
    import javafx.scene.control.TextField;
    import javafx.scene.layout.BorderPane;
    import javafx.scene.layout.HBox;
    import javafx.scene.layout.Pane;
    import javafx.scene.layout.StackPane;
    import javafx.scene.paint.Color;
    import javafx.stage.Stage;

    public class Main extends Application implements EventHandler<ActionEvent>
    {
    Pane pane;
    MenuItem item1, item2, item3, item4;
    Label label;
    Scene scene;
    Menu menu;
    
    
   public static void main(String args[]){
      launch(args);
   }
   
    @Override
       public void start(Stage primaryStage) 
       {
           menu = new Menu("Choose");
           
           item1 = new MenuItem("Add Food");
           item2 = new MenuItem("Add Exercise");
           item3 = new MenuItem("View Log");
           item4 = new MenuItem("Exit");
           
           menu.getItems().addAll(item1, item2, item3, item4);
           
           MenuBar menuBar = new MenuBar(menu);
           menuBar.setTranslateX(200);
           menuBar.setTranslateY(100);
           
           item1.setOnAction(this);
           item2.setOnAction(this);
           item3.setOnAction(this);
           item4.setOnAction(this);
              
           pane = new StackPane();
           
           label = new Label("Welcome to the Health Tracker!\nWhat would you like to do?");
           
           pane.getChildren().addAll(label,menuBar);
           scene = new Scene(pane, 400, 400);
           
           primaryStage.setTitle("Health Tracker");
           
           primaryStage.setScene(scene);
           primaryStage.show();
       }
 

    @Override
    public void handle(ActionEvent event) 
    {
        if(event.getSource() == item1)
        {
            food getfood = new food();
        }
        else if(event.getSource() == item2)
        {
            exercise getExercise = new exercise();
        }
        else if(event.getSource() == item3)
        {
            System.out.print("log");
        }
        else if(event.getSource() == item4)
        {
            System.out.print("exited");
        }
            
    }

    }

Class I am trying to change to

package application;

import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuBar;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class food implements EventHandler<ActionEvent>
{
Pane pane;
MenuItem item1, item2;
Label label;
Scene scene;
Menu menu;
Stage primaryStage;

public void start(Stage primaryStage)
{
    menu = new Menu("Choose");
       
    item1 = new MenuItem("Add Food");
    item2 = new MenuItem("Exit");
    
    menu.getItems().addAll(item1, item2);
    
    MenuBar menuBar = new MenuBar(menu);
    menuBar.setTranslateX(200);
    menuBar.setTranslateY(100);
    
    item1.setOnAction(this);
    item2.setOnAction(this);
    
    pane = new StackPane();
    
    label = new Label("Welcome to the Food tracker!\nWhat would you like to do?");
    
    pane.getChildren().addAll(label,menuBar);
    scene = new Scene(pane, 400, 400);
    
    primaryStage.setTitle("Food Tracker");
       
    primaryStage.setScene(scene);
    primaryStage.show();
}

@Override
public void handle(ActionEvent event) 
{
    if(event.getSource() == item1)
    {
        
    }
    if(event.getSource() == item2)
    {
        
    }
    
}

public food()
{
    primaryStage.show();
}
}

Thanks again for any help:)

Answer 1

There are many things you can correct in the code:

• Naming conventions.
• No need to implement EventHandler for every class.
• Creating Stage instance in Food class. And no need for naming start() method in all classes.

To answer your question, you need to modify the constructor of the Food class as below.

public Food(){
    primaryStage = new Stage();
    start(primaryStage);
}

Having said that, you can optimize the code a lot if you understand the JavaFX concepts correctly. I strongly suggest to go through any JavaFX tutorial.