TicTacToc Bare Minimum. StackOverflow Question https://stackoverflow.com/questions/64312457/get-the-selected-cell-row-and-column-number-of-gridpane

FXMLDocument.fxml

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

<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.RowConstraints?>
<?import javafx.scene.layout.StackPane?>
<?import javafx.scene.text.Font?>


<StackPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="650.0" prefWidth="650.0" style="-fx-background-color: black;" xmlns="http://javafx.com/javafx/8.0.171" xmlns:fx="http://javafx.com/fxml/1" fx:controller="javafxapplication6.FXMLDocumentController">
   <children>
      <GridPane hgap="5.0" maxHeight="-Infinity" maxWidth="-Infinity" vgap="5.0">
        <columnConstraints>
            <ColumnConstraints hgrow="SOMETIMES" maxWidth="200.0" minWidth="200.0" prefWidth="200.0" />
          <ColumnConstraints hgrow="SOMETIMES" maxWidth="200.0" minWidth="200.0" prefWidth="200.0" />
          <ColumnConstraints hgrow="SOMETIMES" maxWidth="200.0" minWidth="200.0" prefWidth="200.0" />
        </columnConstraints>
        <rowConstraints>
          <RowConstraints maxHeight="200.0" minHeight="200.0" prefHeight="200.0" vgrow="SOMETIMES" />
          <RowConstraints maxHeight="200.0" minHeight="200.0" prefHeight="200.0" vgrow="SOMETIMES" />
          <RowConstraints maxHeight="200.0" minHeight="200.0" prefHeight="200.0" vgrow="SOMETIMES" />
        </rowConstraints>
         <children>
            <Label fx:id="lbl0" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
            <Label fx:id="lbl1" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;" GridPane.columnIndex="1">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
            <Label fx:id="lbl2" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;" GridPane.columnIndex="2">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
            <Label fx:id="lbl3" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;" GridPane.rowIndex="1">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
            <Label fx:id="lbl5" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;" GridPane.columnIndex="1" GridPane.rowIndex="1">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
            <Label fx:id="lbl6" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;" GridPane.columnIndex="2" GridPane.rowIndex="1">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
            <Label fx:id="lbl7" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;" GridPane.rowIndex="2">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
            <Label fx:id="lbl8" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;" GridPane.columnIndex="1" GridPane.rowIndex="2">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
            <Label fx:id="lbl9" alignment="CENTER" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" onMouseClicked="#handleMouseClicked" style="-fx-background-color: white;" GridPane.columnIndex="2" GridPane.rowIndex="2">
               <font>
                  <Font size="96.0" />
               </font>
            </Label>
         </children>
      </GridPane>
   </children>
</StackPane>

FXMLDocumentController.java

import java.net.URL;
import java.util.ResourceBundle;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Label;
import javafx.scene.input.MouseEvent;

/**
 *
 * @author sedrick (sedj601)
 */
public class FXMLDocumentController implements Initializable {
    
    int turn = 0;
    
    @FXML
    public void handleMouseClicked(MouseEvent event) {
        Label tempLabel = ((Label)event.getSource());
        if(tempLabel.getText().isEmpty())
        {
            if(turn % 2 == 0)
            {
                tempLabel.setText("X");
            }
            else
            {
                tempLabel.setText("O");
            }
            
            turn++;
        }
    }
    
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        // TODO
    }    
    
}

JavaFXApplication6.java

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

/**
 *
 * @author sedri
 */
public class JavaFXApplication6 extends Application {
    
    @Override
    public void start(Stage stage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("FXMLDocument.fxml"));
        
        Scene scene = new Scene(root);
        
        stage.setScene(scene);
        stage.show();
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }
    
}