Cannot invoke the presenter because it is null, MVP architecture with JavaFX

Question

I create an application follow MVP concept with View using JavaFX. It is working normally with Java Swing; however, when I use JavaFX I encounter this Error.

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1857)
    at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1724)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
    at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
    at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:208)
    at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3897)
    at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1878)
    at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2623)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
    at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
    at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
    at javafx.graphics/com.sun.glass.ui.mac.MacView.notifyMouse(MacView.java:127)
Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:77)
    at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1852)
    ... 48 more
Caused by: java.lang.NullPointerException: Cannot invoke "application.presenter.PatientPresenter.addPatient(application.Patient)" because "this.presenter" is null
    at com.example.demo1/application.view.MainController.addPatientClick(MainController.java:95)
    ... 59 more

This is my Controller.

public class MainController implements Initializable,IPatientView{

    private PatientPresenter presenter;

    //FXML Components

    @FXML
    void addPatientClick(ActionEvent event) {
        String firstName = firstNameTF.getText();
        String lastName = lastNameTF.getText();
        String date = dayPatientCB.getSelectionModel().getSelectedItem() + "/"
                + monthPatientCB.getSelectionModel().getSelectedItem() + "/"
                + yearPatientCB.getSelectionModel().getSelectedItem();
        String gender = genderCB.getSelectionModel().getSelectedItem();
        String phone = phoneTF.getText();
        int id = Integer.parseInt(idPatientTF.getText());

        System.out.println(date);

        Patient patient = new Patient(firstName,lastName,date,gender,phone,id);

        //Why this presenter is null. I've already assign it in bind()
        presenter.addPatient(patient);

        //This is fine. but I need to implement the code the other way
        presenter = new PatientPresenter;
        presenter.addPatient(patient);
    }
    @Override
    public void bind(PatientPresenter presenter) {
        this.presenter = presenter;
    }
}

THis is my Main.

public class Main extends Application {
    @Override
    public void start(Stage stage) throws IOException {

        PatientModel model = new PatientModel();
        IPatientView view = new MainController();

        PatientPresenter presenter = new PatientPresenter(view,model);

        view.bind(presenter);
        model.bind(presenter);

        FXMLLoader fxmlLoader = new FXMLLoader(Main.class.getResource("main-view.fxml"));
        Scene scene = new Scene(fxmlLoader.load(), 892, 749);
        stage.setTitle("Hello!");
        stage.setScene(scene);
        stage.show();



    }

    public static void main(String[] args) {

        launch();

    }
}

Although I assigned this.presenter to presenter, I still get this.presenter is null error. I don't understand why my presenter is null, even though I assign it before.

You must not make a new controller because fxmloader creates that instance when fxml is load — Giovanni Contreras, May 29 '22 at 15:17
Does this answer your question? [JavaFX - how to get instance of the controller object](https://stackoverflow.com/questions/34457811/javafx-how-to-get-instance-of-the-controller-object) — Giovanni Contreras, May 29 '22 at 15:29
Off topic, but JavaFX is really implementing a MVP design for you already. The “controller” is really a presenter, with the FXML playing the role of a passive view. You don’t really need a presenter class that is distinct from the “controller” to implement this pattern. — James_D, May 29 '22 at 19:14
Thank you Giovanni, I tried your solution and it run perfectly. And thanks for your information James. Cheers guys — Nguyễn Hữu Thái, May 29 '22 at 22:17

Cannot invoke the presenter because it is null, MVP architecture with JavaFX

0 Answers0