Javafx - how to acces FXML "objects"

Question

I have some JavaFX components declared in my fxml file.

and how do I get the values of the fields (Username, Password) when the button is pressed? (To perform the login).

  Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
  stage.setTitle("Login");
  stage.setScene(new Scene(root,400,300));
  stage.show();

or is this the complete wrong way to do it?

My Questions:

1. Is it a good idea to declare all fields in the fxml file?
2. How do I get the objects to acces the Values?
3. If its the complete wrong way, how can it be done? (I want to use scenebuilder)

EDIT : https://hastebin.com/qexipogoma.xml <- My FXML fie and my controller

Answer 1

Scene scene = stage.getScene();
Button btn = (Button) scene.lookup("#myBtnID");
TextField txt = (TextField ) scene.lookup("#myTxtID");

you're looking for:

txt.getText();

and

btn.setOnAction( lambda here );

Documentation:

Button

TextField

EDIT: declare ids this way

<TextField fx:id="myTxtID" ...  />