Question

我已经被困在编辑标签的内容几天了。我正在创建一个应用程序，我在开始时加载login.fxml，然后将fxml更改为例如admin_login.fxml，但是当我再次重新加载login.fxml并尝试使用.setText设置Label文本时它会给我一个空指针异常。如果有人可以帮我解决这个问题，我真的很感激。

Main.java

 public class Main extends Application {

Parent root;
FXMLLoader loader;

String login[][] = { {"admin"  ,"admin1234"  },
                     {"student","student1234"},
                     {"teacher","teacher1234"}  };

@Override
public void start(Stage primaryStage) throws Exception{

    loader = new FXMLLoader();
    loader.setLocation(getClass().getResource("login.fxml"));
    root = loader.load();
    primaryStage.setTitle("Practice Test Management System");
    primaryStage.setScene(new Scene(root, 1000, 700));
    primaryStage.show();
}


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

Controller.java

enter code here@FXML Button login_login_bn ;
@FXML TextField login_user_id;
@FXML TextField login_pass;
@FXML Label login_login_error;
@FXML Label login_connection_msg;
@FXML Button admin_set_bn;
@FXML Button admin_about_bn;
@FXML Button admin_users_bn;
@FXML Button teacher_students_bn;
@FXML Button teacher_subjects_bn;
@FXML Button teacher_tests_bn;
@FXML Button teacher_results_bn;
@FXML Button teacher_ques_bn;
@FXML Button teacher_about_bn;
@FXML Button student_about_bn;
@FXML Button student_tests_bn;
@FXML Button student_results_bn;
@FXML Button logout_bn;
@FXML Button login_condatabase_bn;
@FXML TextField super_user_id;
@FXML TextField super_pass;
@FXML Label super_msg_lb;
@FXML Button super_login_bn;
@FXML TextField login_db_name;
@FXML TextField login_db_user_id;
@FXML TextField login_db_pass;
@FXML Label login_db_connection_msg_lb;
@FXML Button login_db_connect_bn;

//Variables
Boolean adminlogin = false;
Boolean studentlogin = false;
Boolean teacherlogin = false;
//Classes
Admin admin = new Admin();
Main main = new Main();
CurrentUser currentuser = new CurrentUser();
DatabaseDriver databasedriver = new DatabaseDriver();

//Scenes
Scene login_scene;



public void dbConnected() throws IOException {
    currentuser.reset();
    Stage stage1;
    Parent root;
    stage1 = (Stage) login_db_connect_bn.getScene().getWindow();

    root = FXMLLoader.load(getClass().getResource("login.fxml"));
    Scene scene2 = new Scene(root, 1000, 700);
    login_connection_msg.setText("database Connected"); //This isn't Working :(
    stage1.setScene(scene2);
    stage1.show();

}

public void superWindow() throws IOException{
    Stage stage1;
    stage1 = (Stage) login_condatabase_bn.getScene().getWindow();
    Parent root;
    root = FXMLLoader.load(getClass().getResource("super_login.fxml"));
    Scene scene2 = new Scene(root,400,400);
    stage1.setScene(scene2);
    stage1.show();
}
public void superLogin() throws IOException {
    if (admin.adminLogin(super_user_id.getText(),super_pass.getText())) {
        Stage stage1;
        Parent root;
        stage1 = (Stage) super_login_bn.getScene().getWindow();
        login_scene = (Scene) super_login_bn.getScene();
        root = FXMLLoader.load(getClass().getResource("login_database_connect.fxml"));
        Scene scene2 = new Scene(root, 600, 400);
        stage1.setScene(scene2);
        stage1.show();
    } else {
        super_msg_lb.setText("Invalid User Id & Password");
    }
}
public void databaseConnect() throws IOException {
    Boolean connection ;
    connection = databasedriver.databaseConnection(login_db_name.getText(),login_db_user_id.getText(),login_db_pass.getText());
    if(connection){
        this.dbConnected();
    }else{
        System.out.println("connection false");
        login_db_connection_msg_lb.setText("Connection not successful....Try Again !");
    }
}
}

在Main中的start函数中加载login.fxml ...然后在控制器中执行superWindow（）然后它在控制器中执行superLogin（）然后它运行databaseConnect（）然后在我加载时运行dbConnected但在dbConnected中运行login.fxml并编辑标签login_connection_msg

login_connection_msg.setText("database Connected");

然后它给了我一个空指针Exception：（

更改为不同的fxml文件然后返回

0 个答案: