How do I use the controller in JavaFX to update images on the fly

Question

Good morning,

I'm trying to create a GUI which has 2 scenes, the first(GUI) has three buttons the second(NQueensGUI) has none. When the button on the first scene opens the second window i want an image on the second window to be fetched and displayed.I am trying to create an N queens viewer, I can do it fine on the console using backtracking and displaying the completed 'N" sized board but now i need to do it in a GUI. I thought of having a grid and filling it with images letting the grid handle the sizing as i will always have N x N items. Anyway thought I would just have a very simple example to start myself of but its not working. I used Scenebuilder to create the simple layouts.

I have some code that opens the second window fine after pressing the button. But then I get the null pointer exception. I think i'm having problems referencing the elements via the controller. If i set the image right at the beginning when the program starts its fine but it's on the fly when things go wrong.Here is my code so far, sorry its a mess but i have tried everything to get it to work.

Anyone please tell me how to access the elements correctly , or am I going down the wrong road..

MAIN

public void start(Stage stage) throws Exception {

    theStage = stage;
    FXMLLoader fxmlLoader = new FXMLLoader();
    fxmlLoader.setLocation(Main.class.getResource("GUI.fxml"));
    Parent root = fxmlLoader.load();
    scene = new Scene(root, 600, 400);
    theStage.setTitle("Project");
    theStage.setScene(scene);
    stage.show();

}

CONTROLLER

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.ResourceBundle;   
import javafx.application.Platform;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;

public class GUIFXMLController implements Initializable {
    @FXML
    private ImageView image1;
    @FXML
    private Pane pane;
    @FXML
    private Stage theStage;

    @FXML
    private javafx.scene.control.Button NQueensButton;

    @FXML
    private void handleNQueensButtonAction(ActionEvent event) throws IOException {
        Stage theStage;
        Parent root;
        theStage = (Stage) NQueensButton.getScene().getWindow();
        FXMLLoader fxmlLoader2 = new FXMLLoader();

        root = FXMLLoader.load(getClass().getResource("NQueensGUI.fxml"));
        GUIFXMLController controller = fxmlLoader2.getController();

        Scene scene = new Scene(root,600,400);
        //controller. // Tried this way as well with same error
        ObservableList<Node> list = pane.getChildren(); //PROBLEM
        //list.add(image1); PROBLEM
        theStage.setScene(scene);
        theStage.show();

    }

    @FXML
    private javafx.scene.control.Button ExitButton;

    public void handleExitButtonAction(ActionEvent event) {
        Platform.exit();

    }

    @Override
    public void initialize(URL location, ResourceBundle resources) {

    }

}

NQUEENSGUI

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.image.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>


<Pane fx:id="pane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="GUIFXMLController">
   <children>
      <ImageView fx:id="image1" fitHeight="150.0" fitWidth="200.0" layoutX="100.0" layoutY="103.0" pickOnBounds="true" preserveRatio="true">
         <image>
            <Image url="queenImageBlack.png" />
         </image>
      </ImageView>
   </children>
</Pane>

GUI

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.geometry.*?>
<?import javafx.scene.shape.*?>
<?import javafx.scene.image.*?>
<?import javafx.scene.text.*?>
<?import java.lang.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>


<Pane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="GUIFXMLController">
   <children>
      <Button fx:id="NQueensButton" layoutX="77.0" layoutY="180.0" mnemonicParsing="false" onAction="#handleNQueensButtonAction" text="N Queens" />
      <Button layoutX="428.0" layoutY="180.0" mnemonicParsing="false" text="Tic Tac Toe" />
      <Button fx:id="ExitButton" layoutX="271.0" layoutY="180.0" mnemonicParsing="false" onAction="#handleExitButtonAction" text="Exit" />
   </children>
</Pane>

ERRORS

 Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1762)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1645)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Node.fireEvent(Node.java:8216)
    at javafx.scene.control.Button.fire(Button.java:185)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3724)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3452)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1728)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2461)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:348)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:273)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:382)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:553)
    at com.sun.glass.ui.View.notifyMouse(View.java:925)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1757)
    ... 43 more
Caused by: java.lang.NullPointerException
    at GUIFXMLController.handleNQueensButtonAction(GUIFXMLController.java:45)
    ... 53 more

Every time you load a fxml file with a `fx:controller` attribute `FXMLLoader` creates a new instance of the controller. If you do not use a `FXMLLoader` instance to load a fxml, the `getController` method returns `null`. (Except if you set the controller instance yourself; BTW: using a loader instance to invoke a static method also wouldn't work.) — fabian, Nov 26 '17 at 10:59
you getting children list null because your root pane has not been initialized yet. — mcd, Nov 26 '17 at 11:16
Ok thanks for the input, i'm still not understanding you @fabian . I have now set the pane = new Pane(); , now if I add these lines ObservableList list = pane.getChildrenUnmodifiable() ; ,System.out.println(list.isEmpty());, i get true but if i change to root.getChildrenUnmodifiable() i get false — Mark, Nov 26 '17 at 11:30
Ok i now can use the getchildren method to change elements but they are not changing on the screen. I can call the tostring method on the element and see that i have changed it from one image to another but the picture does not update — Mark, Nov 26 '17 at 14:47
Start by using a different controller class for each FXML file; it is just way too confusing to use the same class for different controllers that have different controls. Then just fix the code so that you actually load the FXML from the `FXMLLoader` instance, instead of loading it using the static `load(URL)` method. See https://stackoverflow.com/questions/14187963/passing-parameters-javafx-fxml (among many other similar questions). — James_D, Nov 26 '17 at 16:00

How do I use the controller in JavaFX to update images on the fly

0 Answers0