如何将ImageView锚定到其BorderPane区域的中心？

Question

I've got a BorderPane layout with an ImageView, shown below, but the ImageView is always anchored to the top-left corner, and stays there when I resize the window. I would like to the ImageView to maintain anchor at the center of the section it has been bound to (red box). Is this possible using FXML?

FXML:

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

<?import javafx.scene.control.*?>
<?import javafx.scene.Group?>
<?import javafx.scene.image.Image?>
<?import javafx.scene.image.ImageView?>
<?import javafx.scene.layout.*?>

<VBox prefWidth="800.0" prefHeight="600.0" xmlns="http://javafx.com/javafx/8.0.112" xmlns:fx="http://javafx.com/fxml/1">

    <BorderPane xmlns:fx="http://javafx.com/fxml" VBox.vgrow="ALWAYS">
        <top>
            <VBox alignment="TOP_CENTER">
                <ToolBar minHeight="50.0" prefHeight="50.0" prefWidth="800.0" stylesheets="@../css/style.css"
                         GridPane.rowIndex="1">
                    <ImageView fitHeight="35.0" fitWidth="200.0" pickOnBounds="true" preserveRatio="true">
                        <Image url="@../images/toolbar-logo.png"/>
                    </ImageView>
                </ToolBar>
                <MenuBar fx:id="menuBar" prefHeight="0.0" prefWidth="0.0"/>
            </VBox>
        </top>

        <left>
            <StackPane prefWidth="230.0" prefHeight="800.0">
                <ListView fx:id="listView"/>
            </StackPane>
        </left>

        <center>
            <StackPane>
                <ScrollPane>
                    <Group fx:id="selectionGroup">
                        <ImageView fx:id="mainImageView"/>
                    </Group>
                </ScrollPane>
            </StackPane>
        </center>

        <right>
            <TextField promptText="Text"  />
        </right>
    </BorderPane>

</VBox>

Answer 1

Change:

        <StackPane>
            <ScrollPane>
                <Group fx:id="selectionGroup">
                    <ImageView fx:id="mainImageView"/>
                </Group>
            </ScrollPane>
        </StackPane>

To:

        <StackPane>
            <children>
                <ImageView fx:id="mainImageView" fitHeight="150.0" fitWidth="200.0" pickOnBounds="true" preserveRatio="true" />                    
            </children>
        </StackPane>

You may need to adjust the fitWidth and fitHeight attributes.