Label.setText NullPointerException

Question

Hi, the first time here, but here goes:

I have a JavaFX application that dynamically changes FXML interface shortcuts and the data is retrieved from the Player class.

Two classes considered: Player.javaand InterfaceHandler.java.

The player class stores the player data, and I want to pass the details to the Interface class, which sets the text on the labels.

As a test, my FXML interface has only a button and two labels.

If you click on the button, it calls a method handleButtonthat sets locationLabelto "City".

However, if I call a method locationLabel()in the Player class, I get a NullPointerException when called nameLabel.setText(name). Through debugging, I found that the name string in the Interface class is what should be “Dan”.

Can anyone help?

Main class:

public class Main extends Application {

    public void start(final Stage mainStage) throws Exception {

        Parent root = FXMLLoader.load(getClass().getResource("MainScreen.fxml"));
        Scene scene = new Scene(root);
        mainStage.setTitle("Main Screen");
        mainStage.setScene(scene);
        mainStage.show();    
    }

public static void main(String[] args) {
        launch(args);
    }
}

Player Class:

public class Player{

InterfaceHandler ui = new InterfaceHandler();   

 public void setNameLabel() {

    String name = "Dan";
    ui.setName(name);
}

InterfaceHandler Class:

    public class InterfaceHandler implements Initializable {

       public Label nameLabel;
       public Label locationLabel;    

public void handleButton(ActionEvent event) throws IOException {        

        locationLabel.setText("Town");
    }

public void setName(String name){       
        nameLabel.setText(name);
    }    
}

MainScreen.fxml:

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

    <?import java.lang.*?>
    <?import java.net.*?>
    <?import java.util.*?>
    <?import javafx.scene.*?>
    <?import javafx.scene.control.*?>
    <?import javafx.scene.effect.*?>
    <?import javafx.scene.image.*?>
    <?import javafx.scene.layout.*?>
    <?import javafx.scene.text.*?>

    <AnchorPane id="AnchorPane" prefHeight="629.0" prefWidth="600.0" snapToPixel="true" style="-fx-background-color:  beige;" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2" fx:controller="application.InterfaceHandler">
      <children>            
        <Button fx:id="button1" layoutX="512.0" layoutY="381.0" minWidth="14.0" mnemonicParsing="false" onAction="#handleButton" prefHeight="30.0" prefWidth="51.0" text="Town" visible="true" />        

        <Label fx:id="nameLabel" layoutX="57.0" layoutY="8.0" prefWidth="216.0" text="blank" />
        <Label fx:id="locationLabel" layoutX="68.0" layoutY="27.0" prefWidth="193.0" text="blank" />
      </children>
    </AnchorPane>

Answer 1

This is because you entered your LabelsFXML file incorrectly.

Annotate your Labelvars. with annotation FXML:

public class InterfaceHandler implements Initializable {
    @FXML
    public Label nameLabel;
    @FXML
    public Label locationLabel;    

    public void handleButton(ActionEvent event) throws IOException {        
        locationLabel.setText("Town");
    }

    public void setName(String name){       
        nameLabel.setText(name);
    }    
}

, InterfaceHandler - , fx:controller FXML. FXMLLoader InterfaceHandler, FXML. InterfaceHandler Player, InterfaceHandler Player loader.getController, InterfaceHandler FXMLLoader.

FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("MainScreen.fxml"));
Parent root = (Parent)loader.load();
Player player = new Player(loader.getController());
Scene scene = new Scene(root);

. . .

public class Player {
  private InterfaceHandler ui;   

  public Player(InterfaceHandler ui) {
    this.ui = ui;
  }

  public void setNameLabel() {
    String name = "Dan";
    ui.setName(name);
  }
}

Answer 2

- , -, .

<Label . . . " text="ANYTHING"  . . . />