accessing a Pane from another class in javafx - javafx

Question

I am unable to access from another class, I have created two pane with different controllers in one FXML File, second pane has to move around the first pane, on Click Action, and I have loaded an FXML file in second pane, also successfully moved the pane one time, but the second time I want to move it from second controller, but it is giving me an NullPointerException.
this is my main controller where I have moved the pane:
public class MainController implements Initializable {
#FXML
private Pane searchPane;
#FXML
private Pane secondPane;
private TranslateTransition nextTransition;
public Pane getSecondPane() {
return secondPane; // Accessing Pane with this getter method
}
/**
* Initializes the controller class.
*/
#Override
public void initialize(URL url, ResourceBundle rb) {
}
#FXML
private void nextBtnAction(ActionEvent event) {
try {
Parent pessFxml = FXMLLoader.load(getClass().getResource("firstPane.fxml"));
secondPane.getChildren().add(pessFxml);
nextTransition = new TranslateTransition(Duration.millis(300), secondPane);
nextTransition.setToX(searchPane.getLayoutX()-secondPane.getLayoutX());
nextTransition.play();
} catch (IOException ex) {
JOptionPane.showMessageDialog(null, "Form does not found" ,ex.toString(),0);
}
}
}
this is SecondController where I am accessing the pane to move it back smoothly, but its throwing NullPointerException:
please tell me how to solve this
public class SecondController implements Initializable {
MainController mainControll;
/**
* Initializes the controller class.
*/
#Override
public void initialize(URL url, ResourceBundle rb) {
}
#FXML
private void backBtnPessAction(ActionEvent event) {
//here i am putting the second pane to move back
TranslateTransition back = new TranslateTransition(Duration.millis(300), mainControll.getSecondPane());
back.setToX(mainControll.getSecondPane().getLayoutX()-750);
back.play();
}
}

Answer 1

MainController is never initialized in SecondController. You should pass it when creating second controller in nextBtnAction.
MainController code:
private void nextBtnAction(ActionEvent event) {
try {
FXMLLoader loader = new FXMLLoader(getClass().getResource("firstPane.fxml"));
Parent pessFxml = loader.load();
SecondController controller = (SecondController)loader.getController();
controller.setMainController(this);
secondPane.getChildren().add(pessFxml);
nextTransition = new TranslateTransition(Duration.millis(300), secondPane);
nextTransition.setToX(searchPane.getLayoutX()-secondPane.getLayoutX());
nextTransition.play();
} catch (IOException ex) {
JOptionPane.showMessageDialog(null, "Form does not found" ,ex.toString(),0);
}
}
SecondController:
public void setMainController(MainController controller) {
this.mainControll = controller;
}