我有一个2×2 GridPane，每列上都有一个AnchorPane，我想知道用户使用MouseEvent点击了网格的哪一列，但我得到的列和行索引对于每个AnchorPane是：null，完整的项目：

完整的FXML代码：

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

<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.RowConstraints?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.141" fx:controller="sample.Controller" xmlns:fx="http://javafx.com/fxml/1">
   <children>
      <GridPane gridLinesVisible="true" onMouseClicked="#mouseclicked" prefHeight="400.0" prefWidth="600.0">
        <columnConstraints>
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
        </columnConstraints>
        <rowConstraints>
          <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
          <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
        </rowConstraints>
         <children>
            <AnchorPane prefHeight="200.0" prefWidth="200.0" GridPane.columnIndex="0" GridPane.rowIndex="0" />
            <AnchorPane prefHeight="200.0" prefWidth="200.0" GridPane.columnIndex="1" GridPane.rowIndex="0"/>
            <AnchorPane prefHeight="200.0" prefWidth="200.0" GridPane.columnIndex="0" GridPane.rowIndex="1" />
            <AnchorPane prefHeight="200.0" prefWidth="200.0" GridPane.columnIndex="1" GridPane.rowIndex="1" />
         </children>
      </GridPane>
   </children>
</AnchorPane>

FXML控制器：

    package sample;

import javafx.fxml.FXML;
import javafx.scene.Node;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.GridPane;

public class Controller {


    @FXML
    public void mouseclicked(MouseEvent ev){
        Node source = (Node)ev.getSource() ;
        Integer col = GridPane.getColumnIndex(source);
        Integer row = GridPane.getRowIndex(source);

        System.out.println("Column : "+col);
        System.out.println("Row : "+row);
    }
}

主要班级：

    package sample;

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

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root));
        primaryStage.show();

    }


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