javaFX cannot access Scene elements - javafx

Question

I am new to javafX, have run through various tutorials, and googled extensively. I am attempting to write a multiscreen javaFX program whose second screen has a split pane, whose right pane should display a grid and a button. The framework I am using for multiple screens is copied form Angela Caiedo's MultipleScreens Framework tutorial ( https://github.com/acaicedo/JFX-MultiScreen/tree/master/ScreensFramework) .
What works: The screens framework is successful in terms of flipping between my multiple screens.
My problem: I click the button on screen 1 to move to screen 2. Screen 2 successfully shows. On screen 2 I click a button to populate data in my vBox. The code in my controller class for screen 2 is unable to access the vbox (or any other defined containers on this screen).
My main class sets up the controller screens.
public class FieldMapCreator extends Application {
public static String mainID = "main";
public static String mainFile = "MainMapFXMLDocument.fxml";
public static String initialMapID = "initialMap";
public static String initialMapFile = "FXMLMapPicture.fxml";
#Override
public void start(Stage stage) throws Exception {
ScreensController mainContainer = new ScreensController();
mainContainer.loadScreen(FieldMapCreator.mainID, FieldMapCreator.mainFile);
mainContainer.loadScreen(FieldMapCreator.initialMapID, FieldMapCreator.initialMapFile);
mainContainer.setScreen(FieldMapCreator.mainID);
Group root = new Group();
root.getChildren().addAll(mainContainer);
Scene scene = new Scene(root);
stage.setScene(scene);
stage.show();
}
}
I get to the second screen by clicking a button on screen 1. Button1 code looks like:
#FXML
private void initialMapButtonAction(ActionEvent event) {
myController.setScreen(FieldMapCreator.initialMapID);
}
Screen 2 has a button that when clicked executes a method that creates data for the vbox. The fxml for screen 2 is this:
<AnchorPane id="AnchorPane" fx:id="mainAnchorPane" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.40" xmlns:fx="http://javafx.com/fxml/1" fx:controller="FieldMapCreator.FXMLMapPictureController">
<children>
<SplitPane fx:id="mapSplitPane" dividerPositions="0.29797979797979796" layoutX="3.0" layoutY="7.0" prefHeight="400.0" prefWidth="600.0">
<items>
<AnchorPane fx:id="anchorPaneLeft" minHeight="0.0" minWidth="0.0" prefHeight="160.0" prefWidth="100.0">
<children>
<Button fx:id="backButton" layoutX="14.0" layoutY="348.0" mnemonicParsing="false" onAction="#goToMainScreen" text="Back" />
</children>
</AnchorPane>
<AnchorPane fx:id="anchorPaneRight" minHeight="0.0" minWidth="0.0" prefHeight="364.0" prefWidth="401.0">
<children>
<Button fx:id="vBoxShowMap" layoutX="24.0" layoutY="346.0" mnemonicParsing="false" onAction="#buildMapFromNurseries" prefHeight="26.0" prefWidth="91.0" text="show map" />
<VBox fx:id="mapVBox" layoutX="24.0" layoutY="24.0" onMouseClicked="#vBoxMouseClicked" prefHeight="200.0" prefWidth="309.0" />
</children></AnchorPane>
</items>
</SplitPane>
</children>
</AnchorPane>
The code that fails is in the "showInitialMap()" method of the controller class for screen 2. When executed, the last line of this method "mapVBox.getChildren().add(root)", results in a null pointer exception. I expected this to be resolved via the fxml injection. I also tried the commented out code to retrieve "mapVBox" using scene lookup, but it also results in a null pointer exception. The controller code is below:
public class FXMLMapPictureController implements Initializable, ControlledScreen {
ScreensController myController;
static MyNode[][] mainField ;
#FXML
private AnchorPane mainAnchorPane;
#FXML
private static SplitPane mapSplitPane;
#FXML
private AnchorPane anchorPaneLeft;
#FXML
private static AnchorPane anchorPaneRight;
#FXML
private static VBox mapVBox;
#FXML
private Button vBoxShowMap;
/**
* Initializes the controller class.
*/
#Override
public void initialize(URL url, ResourceBundle rb) {
// Should something be in here ??
}
public void goToMainScreen() {
myController.setScreen(FieldMapCreator.mainID);
}
public void showInitialMap() {
int row = userFieldMap.getNumRows();
int col = userFieldMap.getNumCols();
double gridWidth = 309/col;
double gridHeight = 200/row;
Group root = new Group();
// initialize the field
for (int idx = 0; idx < col; idx++) {
for (int jdx = 0; jdx < row; jdx++) {
// create plot
Plot plot = new Plot(idx, jdx, "Plot" + idx + "/" + jdx);
// Create node to hold the Plot
MyNode node = new MyNode(idx*gridWidth, jdx*gridHeight, gridWidth, gridHeight, plot);
// add plot to group
root.getChildren().add(node);
}
}
//Scene myScene = myController.getScene();
//VBox mapVBox = (VBox)myScene.lookup("#mapVBox");
mapVBox.getChildren().add(root);
}
#Override
public void setScreenParent(ScreensController screenParent) {
myController = screenParent;
}
Is there something missing from the initialize() method? I'm wondering if I am not setting something correctly when I change screens. I am able to access the initial screen's containers without problem from all screen 1 methods including the initialize class. When I attempt the same in screen 2, I get the message "screen hasn't been loaded !!!"
Thanks for any help you can provide.

Answer 1

You are using static fields as FXML injection targets which don't work in Java 8 and should not have been implemented to work in any other version, as static UI elements just don't make sense. Here's a bit more detailed answer. Having resorted to a static field most of the time means the software design of the application needs to be reconsidered.