JavaFX FXMLLoader getController NullPointerException - javafx

Question

I have a project in school where I have to develop a program where you first can choose whether you want to save/read to/from a SQL DB or to save/read to/from XML.
I've made a GUI where you can choose between both methods.
The GUI closes after the user clicks on one of the buttons and the MainMenu GUI opens.
Now I need to know in the MainMenuController what the user choose.
I found online a Method to call the MainMenuController inside the first controller, with FXMLLoader.getController().
try {
Stage stage = new Stage();
FXMLLoader Loader = new FXMLLoader();
Parent root = Loader.load(getClass().getResource("MainMenu.fxml"));
MainMenuController mc = Loader.getController();
mc.setSave("sql");
Scene scene = new Scene(root);
stage.setScene(scene);
stage.show();
}
catch (Exception e) {
e.printStackTrace();
}
MainMenuController
public class MainMenuController {
private String save = null;
public void setSave(String save) {
this.save=save;
}
public String getSave() {
return save;
}
}
But when i try to access a method in MainMenuController I get a NullPointerException for
mc.setSave("sql")

Answer 1

First ,to understand this issue ,you should make some tricks to detect where is your problem.When you do :
System.out.println(mc);
You will find the result is null.So you can not call setSave("sql") with null object,you got a null controller because your did not specify the location of your file,but you can change some lines to resolve your problem :
try {
Stage stage = new Stage();
FXMLLoader fxm = new FXMLLoader(getClass().getResource("MainMenu.fxml"));
Parent parent = (Parent) fxm.load();
Scene scene = new Scene(parent);
stage.setScene(scene);
stage.show();
FirstController mc = fxm.getController();
System.out.println(mc);
mc.setSave("sql");
} catch (Exception e) {
e.printStackTrace();
}

Answer 2

You are calling the static method FXMLLoader.load(URL). Because this is a static method, it has no effect on the state of the FXMLLoader instance you created; specifically the controller field is not set.
Instead, set the location on the FXMLLoader instance, and call the instance method load():
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("MainMenu.fxml"));
// or just FXMLLoader loader = new FXMLLoader(getClass().getResource("MainMenu.fxml"));
Parent root = loader.load();