NullPointerException calling setText after loading fxml

[Michael Peremsky]

It has been over 5 years since I've worked with JavaFX. This seems like such a simple thing, yet I am not sure what I am missing. I am just trying to set the value of a text field, but I am getting a null pointer exception. It is being called after the loader, so I am not totally sure what I am missing.

@FXML
   Text txtHeader;

public LoginController(ResourceBundle bundle, UserRole userRole) {
 
      FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("Login.fxml"), bundle);
      fxmlLoader.setController(this);

      try {

         setScene(new Scene((Parent) fxmlLoader.load()));
         this.setTitle(bundle.getString("title.login"));
         this.txtHeader.setText(userRole.toString() + " " + "User");      <=== HERE

         FXUtils.addTextLimiter(tfUsername, Validations.USERNAME_MAX_LEN);
         FXUtils.addTextLimiter(pfPassword, Validations.PWD_MAX_LEN);

         Platform.runLater(new Runnable() {
            @Override
            public void run() {
               tfUsername.requestFocus();
            }
         });
      } catch (IOException e) {
         DialogHelper.showException(bundle.getString("exception.login_ttl_init_failure"), bundle.getString("exception.login_hdr_init_failure"), e);
      }
   }

Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.text.Text.setText(String)" because "this.txtHeader" is null

[Campbell Ritchie]

Is that the constructor? You seem to have declared txtHeader but neither given it private access, nor initialised the reference. A field declared and not initialised implicitly points to null.

[Campbell Ritchie]

Michael Peremsky wrote:. . . because "this.txtHeader" is null

If only all exception messages would give such useful information!

[Michael Peremsky]

I thought that by tying the fxid to the object in the fxml, it was supposed to create an instance of the object on the load.

            <Text fx:id="txtHeader" strokeType="OUTSIDE" strokeWidth="0.0" styleClass="popup-header" GridPane.columnSpan="2">
               <font>
                  <Font  size="20.0" />
               </font>
            </Text>

Is this not the case? Again, it has been over 5 years.

If I created an object

  txt = new Text("value");

would I then need to reassign it to the fxml object? How exactly?

[Michael Peremsky]

Resolved. Not sure what was wrong, perhaps naming was off. But it is now loading the text properly.

[Campbell Ritchie]

Sorry, I don't know enough FXML to help there.

[Lou Hamers]

Michael Peremsky wrote:I thought that by tying the fxid to the object in the fxml, it was supposed to create an instance of the object on the load.

FXMLLoader.load() does normally trigger @FXML field injection.

But you might want to use the initialize() method for initializing the field component rather than the constructor. Most of my controllers don't even have explict constructors. The initialize() method is safe to access FXML injected stuff from (implement Initializable). Actually I'd also suggest using fx:controller in the FXML rather than setController() which is a bit unorthodox IMO. It's more common for me to see it done something like this (I often put the FXMLLoader parts into a utility class):

public class TestFxml extends Application {
    
    @Override
    public void start(Stage stage) {
        
        try {
            FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("Test.fxml"));
            stage.setScene(new Scene(fxmlLoader.load()));
            fxmlLoader.getController();//Sometimes you'll also want to get the controller, for example to do some quick and dirty DI
        } catch (IOException e) {
            e.printStackTrace();//Well, do something better...
        }
        
        stage.show();
    }
}

public class TestController implements Initializable {

    @FXML
    private VBox testingVb;
    @FXML
    private Button testBtn;
    
    public TestController() {
        System.out.println("Cons: " + testingVb);
    }
    
    @Override
    public void initialize(URL location, ResourceBundle resources) {
        System.out.println("initialize: " + testingVb);
    }
}

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

<?import javafx.scene.control.Button?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.VBox?>

<AnchorPane fx:controller="com.test.jfxtests.TestController" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="600.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/17" xmlns:fx="http://javafx.com/fxml/1">
   <children>
      <VBox fx:id="testingVb" layoutX="32.0" layoutY="53.0" prefHeight="175.0" prefWidth="295.0">
         <children>
            <Button fx:id="testBtn" mnemonicParsing="false" text="Button" />
         </children>
      </VBox>
   </children>
</AnchorPane>

Safe to access injected fields after initialize():

> Task :TestFxml.main()
Cons: null
initialize: VBox[id=testingVb]

Just make sure your controller implements Initializable.

Gluon Scene Builder will set the fx:controller attribute for you if you select it on the Controller area of the left panel. Rarely needed to mess with FXML directly. Some/all IDEs have FXML plugins also which will automatically generate and correct your @FXML injected stuff, helps eliminate simple mistakes.