JavaFX : Pass parameters while instantiating controller class

Question

I am working on JavaFX application right now. All my gui is in .fxml format and through controller class manages all GUI components. However, I have difficulties with instantiating the controller class before I load FXML loader. I was unable to find a good solution for my question from others on stackoverflow, therefore this is not a duplicate question.

The reason why I am instantiating the controller class is that I want to pass some parameters so that these parameters will be displayed in GUI.

I am loading an FXML file the following way:

/*  * for Work Order button  */ @FXML private void pressWorkOrder() throws Exception{      WorkOrderController wo = new WorkOrderController("ashdkjhsahd");    //instantiating constructor           Parent parent = FXMLLoader.load(getClass().getResource("/fxml/WorkOrder.fxml"));             Scene scene = new Scene(parent);     Stage stage = new Stage();     stage.setScene(scene);     stage.setTitle("Word Order");     stage.setResizable(false);     stage.show(); } 

And here is my actual Controller class:

public class WorkOrderController implements Initializable{       @FXML      private Button summary;      private String m,n;       public WorkOrderController(String str) {          // TODO Auto-generated constructor stub          m = str;      }         //for testing      public void set(String str){          m = str;      }         @FXML      public void check(){          System.out.println("Output after constructor was initialized " + m);      }       @Override      public void initialize(URL location, ResourceBundle resources) {         // TODO Auto-generated method stub      }  } 

And I get this Exception:

at javafx.fxml.FXMLLoader.processStartElement(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.load(Unknown Source) at MainController.pressWorkOrder(MainController.java:78) ... 57 more Caused by: java.lang.InstantiationException: WorkOrderController at java.lang.Class.newInstance(Unknown Source) at sun.reflect.misc.ReflectUtil.newInstance(Unknown Source) ... 71 more Caused by: java.lang.NoSuchMethodException: WorkOrderController.<init>() at java.lang.Class.getConstructor0(Unknown Source) ... 73 more 

Answer 1

The two easiest ways of doing it for small applications are :

1. Do not specify the fx:controller in the fxml. Create a controller instance by passing data to it and then pass it to the FXMLLoader.

2. Specify the fx:controller in the fxml. Fetch the controller instance from the FXMLLoader and pass the data to the controller.

The following are the examples for both the above said types. Each of the example have 3 components :

• FXML - The FXML file, which doesn't have the fx:controller declaration for the first type and has it for the second type.
• Controller - Has a constructor for the first type. Has setter methods for the second type.
• Main - Used for loading FXML and pass data to the controller. For first case, it sets the controller to FXMLLoader. While in second, it fetches the controller from the FXMLLoader.

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1. Create a controller instance manually

FXML - Do not specify the fx:controller

<?xml version="1.0" encoding="UTF-8"?>  <?import javafx.scene.layout.FlowPane?> <?import javafx.scene.control.Label?>  <FlowPane fx:id="root" xmlns:fx="http://javafx.com/fxml">     <children>         <Label fx:id="firstName" text="" />         <Label fx:id="lastName" text="" />     </children> </FlowPane> 

Controller - create a Constructor to accept default values

import javafx.beans.property.SimpleStringProperty; import javafx.beans.property.StringProperty; import javafx.fxml.FXML; import javafx.fxml.Initializable; import javafx.scene.control.Label;  import java.net.URL; import java.util.ResourceBundle;  public class SampleController implements Initializable {      private StringProperty firstNameString = new SimpleStringProperty();     private StringProperty lastNameString = new SimpleStringProperty();      /**      * Accepts the firstName, lastName and stores them to specific instance variables      *       * @param firstName      * @param lastName      */     public SampleController(String firstName, String lastName) {         firstNameString.set(firstName);         lastNameString.set(lastName);     }      @FXML     Label firstName;      @FXML     Label lastName;      @Override     public void initialize(URL location, ResourceBundle resources) {         firstName.setText(firstNameString.get());         lastName.setText(lastNameString.get());     } } 

Main - Create a Controller instance, by passing value into it and then pass it to the FXMLLoader

import javafx.application.Application; import javafx.fxml.FXMLLoader; import javafx.scene.Scene; import javafx.scene.layout.FlowPane; import javafx.stage.Stage;  public class Main extends Application {     @Override     public void start(Stage primaryStage) throws Exception {         FXMLLoader loader = new FXMLLoader(getClass().getResource("Sample.fxml"));          // Create a controller instance         SampleController controller = new SampleController("itachi", "uchiha");         // Set it in the FXMLLoader         loader.setController(controller);         FlowPane flowPane = loader.load();         Scene scene = new Scene(flowPane, 200, 200);         primaryStage.setScene(scene);         primaryStage.show();     }      public static void main(String[] args) {         launch(args);     } } 

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2. Fetch a controller instance from FXMLLoader

FXML - Has specified the fx:controller

<?xml version="1.0" encoding="UTF-8"?>  <?import javafx.scene.layout.FlowPane?> <?import javafx.scene.control.Label?>  <!-- Controller Specified --> <FlowPane fx:id="root" xmlns:fx="http://javafx.com/fxml" fx:controller="SampleController">     <children>         <Label fx:id="firstName" text="" />         <Label fx:id="lastName" text="" />     </children> </FlowPane> 

Controller - Has Setter methods to accept input

import javafx.fxml.FXML; import javafx.fxml.Initializable; import javafx.scene.control.Label;  import java.net.URL; import java.util.ResourceBundle;  public class SampleController implements Initializable {      @FXML     Label firstName;      @FXML     Label lastName;      @Override     public void initialize(URL location, ResourceBundle resources) {      }      /**      * Accepts a String and sets it to the firstName Label      *      * @param firstNameString      */     public void setFirstName(String firstNameString) {         firstName.setText(firstNameString);     }      /**      * Accepts a String and sets it to the lastName Label      *      * @param lastNameString      */     public void setLastName(String lastNameString) {         lastName.setText(lastNameString);     } } 

Main - Fetches the Controller instance from FXMLLoader after calling the load() and then calls the setter methods to pass data.

import javafx.application.Application; import javafx.fxml.FXMLLoader; import javafx.scene.Scene; import javafx.scene.layout.FlowPane; import javafx.stage.Stage;  public class Main extends Application {     @Override     public void start(Stage primaryStage) throws Exception {         FXMLLoader loader = new FXMLLoader(getClass().getResource("Sample.fxml"));         FlowPane flowPane = loader.load();         // Get the Controller from the FXMLLoader         SampleController controller = loader.getController();         // Set data in the controller         controller.setFirstName("itachi");         controller.setLastName("uchiha");         Scene scene = new Scene(flowPane, 200, 200);         primaryStage.setScene(scene);         primaryStage.show();     }      public static void main(String[] args) {         launch(args);     } }