JavaFX：尝试使对话框出现在应用程序之前

Question

The code:

import java.io.IOException;
import java.util.Optional;

/**
 * Version 0.8
 * @author htha9587
 * 7-7-16
 */

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.control.TextInputDialog;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class ChatbotRunner extends Application 
{
    private Stage primaryStage;
    private BorderPane rootLayout;
    /**
     * Sets stage with the scene.
     */
    @Override
    public void start(Stage primaryStage) 
    {   
        //Sets up dialog before main application.
        TextInputDialog dialog = new TextInputDialog("Harrison");
        dialog.setTitle("ChatbotFX");
        dialog.setHeaderText("This message brought to you by ChatbotFX.");
        dialog.setContentText("What's your name?");
        dialog.initOwner(primaryStage);
        //Sets Icon.
        dialog.setGraphic(new ImageView(this.getClass().getResource("HAL.png").toString()));
        //Retrieves response value.
        Optional<String> result = dialog.showAndWait();
        if (result.isPresent())
        {
            dialog.setResult("Hello " + result.get());
        }

        //Sets main stage and scene.
        this.primaryStage = primaryStage;
        this.primaryStage.setTitle("ChatbotFX");

        //Sets Application Icon.
        this.primaryStage.getIcons().add(new Image("file:resources/images/HAL.png"));

        initRootLayout();
    }

    public void initRootLayout() {
        try {
            // Load root layout from fxml file.
            FXMLLoader loader = new FXMLLoader(ChatbotRunner.class.getResource("view/ChatbotView.fxml"));
            rootLayout = (BorderPane) loader.load();

            // Show the scene containing the root layout.
            Scene scene = new Scene(rootLayout);
            primaryStage.setScene(scene);
            primaryStage.show();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * Returns main stage.
     */
    public Stage getPrimaryStage()
    {
        return primaryStage;
    }

    /**
     * Runs the program.
     * @param args
     */
    public static void main(String[] args) 
    {
        launch(args);
    }
}

My planning of the project is this: Have a Text-Input dialog show up before the main application and return the user's name. Then the dialog will close and the main application will then open up.

Error Message:

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
    at javafx.scene.control.HeavyweightDialog.updateStageBindings(HeavyweightDialog.java:329)
    at javafx.scene.control.HeavyweightDialog.initOwner(HeavyweightDialog.java:123)
    at javafx.scene.control.Dialog.initOwner(Dialog.java:479)
    at chat.ChatbotRunner.start(ChatbotRunner.java:37)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
    ... 1 more
Exception running application chat.ChatbotRunner

Thanks in advance.

Answer 1

Due to the primary Stage not being shown the Dialog cannot use it as an owner. This will run if you remove the call to initOwner().