运行JavaFX代码时，应用程序将不会显示

Question

我正在开发一个非常小、简短的应用程序，用于计算即将召开的会议的费用。在添加事件处理程序之前，运行代码时应用程序显示良好。一切似乎都在控制之中，所以我不确定发生了什么。任何见解都将不胜感激。

//JavaFX imports
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.RadioButton;
import javafx.scene.control.ToggleGroup;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
public class ConferenceRegistration extends Application {
// Create radio buttons for conference event options
RadioButton generalAdmissionButton, studentAdmissionButton, keynoteDinnerButton, eCommerceButton, webFutureButton,
advancedJavaButton, securityButton;
Label labelAdmission, labelOptionalEvents, totalChargesLabel;
Button totalCharges;
public static void main(String[] args) {
// launch the application
launch(args);
}
@Override
public void start(Stage stage) throws Exception {
// Label for admission type selection
labelAdmission = new Label("Please select your Admission type: ");
// mandatory selection for conference
generalAdmissionButton = new RadioButton("General Admission: $895");
studentAdmissionButton = new RadioButton("Student Admission: $495");
// Create toggle group for either admission group
ToggleGroup optionalEvents = new ToggleGroup();
generalAdmissionButton.setToggleGroup(optionalEvents);
studentAdmissionButton.setToggleGroup(optionalEvents);
// Label for optional conference events
labelOptionalEvents = new Label("Please Select All Optional Events You Will Be Attending: ");
// set values for optional conference events
keynoteDinnerButton = new RadioButton("Keynote Speech Dinner: $30");
eCommerceButton = new RadioButton("Introduction to E-commerce: $295");
webFutureButton = new RadioButton("The Future of the Web: $295");
advancedJavaButton = new RadioButton("Advanced Java Programming: $395");
securityButton = new RadioButton("Network Security: $395");
// Button for calculating total Conference charges
totalCharges = new Button("Calculate Total");
totalCharges.setOnAction(new TotalChargesCalculator());
// create Vbox container and add all labels, buttons
VBox vbox = new VBox(10, labelAdmission, generalAdmissionButton, studentAdmissionButton, labelOptionalEvents,
keynoteDinnerButton, eCommerceButton, webFutureButton, advancedJavaButton, securityButton, totalCharges,
totalChargesLabel);
// format vbox
vbox.setAlignment(Pos.CENTER);
vbox.setPadding(new Insets(20));
// create and set scene
Scene scene = new Scene(vbox);
stage.setTitle("Conference Registration");
stage.setScene(scene);
// show stage
stage.show();
}
class TotalChargesCalculator implements EventHandler<ActionEvent> {
@Override
public void handle(ActionEvent arg0) {
int result = 0;
try {
// check which radio buttons are selected
if (generalAdmissionButton.isSelected()) {
result = result + 895;
}
if (studentAdmissionButton.isSelected()) {
result = result + 495;
}
if (keynoteDinnerButton.isSelected()) {
result = result + 295;
}
if (eCommerceButton.isSelected()) {
result = result + 295;
}
if (webFutureButton.isSelected()) {
result = result + 295;
}
if (advancedJavaButton.isSelected()) {
result = result + 395;
}
if (securityButton.isSelected()) {
result = result + 395;
}
totalChargesLabel.setText(String.valueOf(result));
} catch (Exception e) {
if (generalAdmissionButton.isSelected() == false || studentAdmissionButton.isSelected() == false) {
totalChargesLabel.setText("Please Select Admission Type.");
}
}
}
}
}

谢谢你抽出时间。我期待着学习我所忽视的东西。

Answer 1

您没有初始化totalChargesLabel。

在将其添加到VBox:之前，将其初始化为空Label

totalChargesLabel = new Label();