Referencing a @FXML TextField from another class, but getting NullPointerException

Question

I am trying to reference a TextField (@FXML) from another controller class, but I get NullPointerException. The following code explains the project. I want to understand why this happens. Thank you for your efforts in advance!

Foo.fxml file

//Foo.fxml
...
  <TextField fx:id="textField" prefWidth="54" text="someText" />
...

FooController.java file

//FooController.java
public class FooController implements Initializable {

        @FXML
        private TextField textField;

        public TextField gettextField(){
            return textField;
        }
    }

MainController.java file

//MainController.java
public class MainController implements Initializable {

    private FooController fooControllerClass;

    @Override
    public void initialize(URL url, ResourceBundle rb) {
      System.out.println(fooControllerClass.gettextField().getText()); // this line throws java.lang.NullPointerException
    }
}

Main.java file

//Main.java
public class Main extends Application {
    @Override
    public void start(Stage stage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("Main.fxml"));
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
        }
    public static void main(String[] args) {launch(args);}
}

Stacktrace:

java.lang.NullPointerException
file:/home/vaib/shared/NetBeansProjects/JRAD/dist/run1408613327/Main.jar!/jrad/Main.fxml
  at jrad.MainController.initialize(MainController.java:6)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2185)  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2185)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2061)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2778)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2757)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2743)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2730)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2719)
  at jrad.Main.start(Main.java:34)
  at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:319)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2185)
  at com.sun.javafx.application.PlatformImpl$5.run(PlatformImpl.java:216)
  at com.sun.javafx.application.PlatformImpl$4$1.run(PlatformImpl.java:179)
  at com.sun.javafx.application.PlatformImpl$4$1.run(PlatformImpl.java:176)
  at java.security.AccessController.doPrivileged(Native Method)
  at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:176)
  at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:76)
  at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
  at com.sun.glass.ui.gtk.GtkApplication$3$1.run(GtkApplication.java:89)
  at java.lang.Thread.run(Thread.java:744)

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.javafx.main.Main.launchApp(Main.java:698)
    at com.javafx.main.Main.main(Main.java:871)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:403)
    at com.sun.javafx.application.LauncherImpl.access$000(LauncherImpl.java:47)
    at com.sun.javafx.application.LauncherImpl$1.run(LauncherImpl.java:115)
    at java.lang.Thread.run(Thread.java:744)
Caused by: java.lang.NullPointerException
    at jrad.JRADController.initialize(JRADController.java:196)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2185)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2061)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2778)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2757)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2743)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2730)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2719)
    at jrad.JRAD.start(JRAD.java:34)
    at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:319)
    at com.sun.javafx.application.PlatformImpl$5.run(PlatformImpl.java:216)
    at com.sun.javafx.application.PlatformImpl$4$1.run(PlatformImpl.java:179)
    at com.sun.javafx.application.PlatformImpl$4$1.run(PlatformImpl.java:176)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:176)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:76)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication$3$1.run(GtkApplication.java:89)
    ... 1 more
Java Result: 1

Answer 1

So I think you have

Main.fxml

<!-- root element -->< ... fx:controller="MainController">
...
<fx:include source="foo.fxml"/>
...

If so, put an fx:id on the fx:include:

<fx:include fx:id="foo" source="foo.fxml"/>

and then you can inject the controller for foo.fxml into MainController using an @FXML annotation:

public class MainController {
  @FXML
  private FooController fooController ;
  // ...
}

The rule here is that if the fx:id of the include is "x", then the variable name for the injected controller must be "xController". See Nested Controller s in the intro to FXML.