JavaFX

Question

在这个程序中，我只使用了一个场景，但是改变了它的根节点。

最初，程序显示 "Welcome" 屏幕 (welcomeRoot)。但是当我按下那里的 "Log in" 按钮时，屏幕会变为 "Choose game mode" 屏幕，即使在我的代码中它清楚地表明 "logInRoot".

肯定不是像gmodeRoot那样初始化了logInRoot。

这里是代码的摘录，为清楚起见，进行了缩减。

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene; 
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextArea;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class WhatsWrong extends Application { 
    public void start(Stage theStage) throws Exception {

        // Fields
        VBox welcomeRoot = new VBox(20);
        VBox logInRoot = new VBox(20);
        VBox signUpRoot = new VBox(20);
        VBox gmodeRoot = new VBox(20);
        VBox singleplayerRoot = new VBox(20);
        VBox multiplayerRoot = new VBox(20);
        VBox statsRoot = new VBox(20);
        String currentUser = "";


        // Welcome screen
        Label theWelcomeMessage = new Label("Welcome to the Morse code learning program");
        Label welcomeLabel = new Label("Welcome screen");
        Button logInBtn = new Button("Log in");
        logInBtn.setOnAction(e -> theStage.getScene().setRoot(logInRoot));    // correct link...
        Button signUpBtn = new Button("Sign in");
        logInBtn.setOnAction(e -> theStage.getScene().setRoot(signUpRoot));
        Button unloggedBtn = new Button("Continue unlogged");
        logInBtn.setOnAction(e -> theStage.getScene().setRoot(gmodeRoot));  
            // This button links directly to choosing the game mode.

        welcomeRoot.getChildren().addAll(theWelcomeMessage, welcomeLabel, logInBtn, signUpBtn, unloggedBtn);


        // Log in screen
        Button logInGoBackBtn = new Button(/*back arrow drawing here*/);
        logInGoBackBtn.setOnAction(e -> theStage.getScene().setRoot(welcomeRoot));
        Label logInLabel = new Label("Log in");
        TextArea logInUsernameInput = new TextArea();
        logInUsernameInput.setPromptText("Username - only letters and numbers, max length 15");
        logInUsernameInput.setId("username");
        TextArea logInPasswordInput = new TextArea();
        logInPasswordInput.setPromptText("Password - at least one letter, number and special character");
        logInPasswordInput.setId("password");
        logInPasswordInput.getText();
        Button logInConfirmBtn = new Button("Continue");
        logInConfirmBtn.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                // verify, display error message if correct, save username to currentUsername if correct.
            }
        });
        Label logInUsernameError = new Label(/*x symbol here*/"Error - username taken or invalid");
        Label logInPasswordError = new Label(/*x symbol here*/"Error - password invalid");    
            // input these into the root and delete if need be

        logInRoot.getChildren().addAll(logInGoBackBtn, logInLabel, logInUsernameInput, logInPasswordInput, logInConfirmBtn);


        // Sign up screen
        // code and some pseudocode here - deleted to save space


        // Choose game mode screen
        Button gmodeGoBackBtn = new Button(/*back arrow drawing here*/);
        gmodeGoBackBtn.setOnAction(/*If logged in, display a pop-up about logging-off*/e -> theStage.getScene().setRoot(welcomeRoot));
        Label gmodeLabel = new Label("Choose the game mode");
        Button gmodeTo1PlayerBtn = new Button("Singleplayer");
        gmodeTo1PlayerBtn.setOnAction(e -> theStage.getScene().setRoot(singleplayerRoot));
        Button gmodeToMultiBtn = new Button("Multiplayer");
        gmodeToMultiBtn.setOnAction(e -> theStage.getScene().setRoot(multiplayerRoot));
        Button gmodeToStatsBtn = new Button("Statistics");
        gmodeToStatsBtn.setOnAction(e -> theStage.getScene().setRoot(statsRoot));

        gmodeRoot.getChildren().addAll(gmodeGoBackBtn, gmodeLabel, gmodeTo1PlayerBtn, gmodeToMultiBtn, gmodeToStatsBtn);


        // etc.


        // Dealing with stage
        theStage.setTitle("Morse code - educational program");
        Scene theScene = new Scene(welcomeRoot);    // Replace with logInRoot, and login screen shows up, as expected.
        theStage.setScene(theScene);
        theStage.show();
    }

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

P.S。 "excerpt";希望我能让你发笑 ;)

Answer 1

这里您创建了 3 个按钮，但您只为 logInBtn 设置了动作侦听器：

Button logInBtn = new Button("Log in");
logInBtn.setOnAction(e -> theStage.getScene().setRoot(logInRoot));
Button signUpBtn = new Button("Sign in");
logInBtn.setOnAction(e -> theStage.getScene().setRoot(signUpRoot));
Button unloggedBtn = new Button("Continue unlogged");
logInBtn.setOnAction(e -> theStage.getScene().setRoot(gmodeRoot));

向同一个按钮添加另一个侦听器将覆盖之前设置的任何侦听器，这就是为什么您的根设置为 gmodeRoot 以及您看到错误消息的原因。

我猜您想将其更改为：

Button logInBtn = new Button("Log in");
logInBtn.setOnAction(e -> theStage.getScene().setRoot(logInRoot));
Button signUpBtn = new Button("Sign in");
signUpBtn.setOnAction(e -> theStage.getScene().setRoot(signUpRoot));
Button unloggedBtn = new Button("Continue unlogged");
unloggedBtn.setOnAction(e -> theStage.getScene().setRoot(gmodeRoot));

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