javafx：textfield总是输出“”

Question

我想在Javafx上进行测试驱动器，并尝试创建一个可以划分两个值的应用程序，但是每当我运行它时，它都会使TextField输出为“”。 这是我的代码：

package com.example.javafxprojecttest;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

import static java.lang.System.*;

public class Divide extends Application {
    @Override
    public void start(Stage stage) throws Exception {
        stage.setTitle("Divide values");
        Label divisionVal1 = new Label("Dividend : ");
        TextField dividend = new TextField();
        TextField divisor = new TextField();
        Label divisionVal2 = new Label("Divisor : ");
        Button divide = new Button("Divide");
        String dividendString = dividend.getText();
        String divisorString = divisor.getText();
        double d = Double.parseDouble(dividendString) / Double.parseDouble(divisorString);
        divide.setOnAction(e -> {
                    out.println(d);
                }
        );
        GridPane root = new GridPane();
        root.addRow(0, divisionVal1, dividend);
        root.addRow(1, divisionVal2, divisor);
        root.addRow(2, divide);
        Scene scene = new Scene(root, 400, 400);
        stage.setScene(scene);
        stage.show();
    }

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

输出：

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:465)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:364)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1071)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:901)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:196)
    at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.NumberFormatException: empty String
    at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
    at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
    at java.base/java.lang.Double.parseDouble(Double.java:651)
    at com.example.javafxprojecttest/com.example.javafxprojecttest.Add.start(Add.java:24)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:847)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(PlatformImpl.java:484)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:457)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:456)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
    ... 1 more
Exception running application com.example.javafxprojecttest.Add

Process finished with exit code 1

我不知道如何解决此问题，也不知道我必须添加这个问题才能使您能够回答它。 我试图在Stackoverflow上查看许多其他问题，但发现没有什么对我有用，我对Stackoverflow（提出问题）也很新，所以我对记录错误的记录不太了解。

Answer 1

好吧，我自己只将所有这些都转移到按钮动作中就得到了。

public void start(Stage stage) throws Exception {
    stage.setTitle("Divide values");
    Label divisionVal1 = new Label("Dividend : ");
    TextField dividend = new TextField();
    TextField divisor = new TextField();
    Label divisionVal2 = new Label("Divisor : ");
    Button divide = new Button("Divide");
    divide.setOnAction(e -> {
        String dividendString = dividend.getText();
        String divisorString = divisor.getText();
        double d = Double.parseDouble(dividendString) / Double.parseDouble(divisorString);
                out.println(d);
            }
    );