Getting access to ui elements in different fxml file

Question

I have a FXML-application with a main.fxml, which includes two other fxml files. Each of these fxml files has its own controller class.

My question is, of how to get access to objects from a specific controller, although these objects are defined on another fxml file.

The following code is just a minimal example. I thought it was a good idea to split ui elements in different fxml files, because they are getting larger and larger.

My main fxml:

<VBox xmlns:fx="http://javafx.com/fxml/1" fx:controller="MainController">
   <fx:include fx:id="top" source="top.fxml"/>
   <fx:include fx:id="bottom" source="bottom.fxml"/>
</VBox>

top.fxml:

<VBox fx:id="vbox" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2" fx:controller="ControllerTop">
  <children>
    <Button fx:id="topbtn" onAction="#printOutput" text="OK" />
  </children>
</VBox>

bottom.fxml

<VBox fx:id="vbox" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2" fx:controller="ControllerBottom">
  <children>
    <Button fx:id="bottombtn" onAction="#printOutput" text="OK" />
  </children>
</VBox>

For top.fxml i have created this controller class:

public class ControllerTop {
    @FXML public Button topbtn;
    @FXML public Button bottombtn;

    @FXML
    public void printOutput() {
        System.out.println("Hello from top button");
        topbtn.setDisable(true); //OK!
        bottombtn.setDisable(false); //Failed
    }
}

Of course bottombtn is defined in bottom.fxml and has its own controller. The problem is, that bottombtn of printOut() of this ControllerTop results in a NullPointerException. So i need help by accessing objects in a nice and smart way.

Thanks

Answer 1

in main controller:

public class MainController {
/**
 * var name has to be topController
 */
public TopController topController;
/**
 * var name has to be bottomController
 */
public BottomController bottomController;

public void initialize(){
    Button topbtn=topController.topbtn;
    Button bottombtn=bottomController.bottombtn;
    topbtn.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent event) {
            System.out.println("Hello from top button");
            topbtn.setDisable(true); //OK!
            bottombtn.setDisable(false); //Failed
        }
    });

}
}

bottom.fxml:

    <VBox fx:id="vbox" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2" fx:controller="BottomController">
  <children>
    <Button fx:id="bottombtn" text="OK" />
  </children>
</VBox>

top.fxml:

 <VBox fx:id="vbox" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2" fx:controller="TopController">
  <children>
    <Button fx:id="topbtn" text="OK" />
  </children>
</VBox>

and in class TopController and BottomController set @FXML public Button **btnName**;

BottomController:

public class BottomController {    
    public Button bottombtn;
}

TopController:

public class TopController {
    public Button topbtn;
}

Another option it to use initialize at MainController to set the value of bottombtn in topController