This might sound like a duplicate since there are tons of questions regarding resizing a child Pane to fit Parent Pane but I have tried almost everything without any luck.
My SplitPane is located inside an AnchorPane and this is my original code:
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity"  
    minWidth="-Infinity" prefHeight="792.0" prefWidth="1055.0" 
    xmlns="http://javafx.com/javafx/null" xmlns:fx="http://javafx.com/fxml/1"
     fx:controller="com.judeochalifu.stock_manager.controller.NewSupplierController">
   <children>
      <SplitPane fx:id="splitPlane" dividerPositions="0.5" layoutX="371.0" layoutY="229.0" prefHeight="792.0" prefWidth="1055.0"orientation="VERTICAL"  AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
    <items>
      <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0" prefWidth="160.0" />
      <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0" prefWidth="160.0" />
    </items>
    </SplitPane>
 </children>
</AnchorPane>
This is the output without resizing:
When I drag the window to increase width or height, this is what I get:
The desired result is for the SplitPane to expend as the window expands, that is to resize according to the width and height of the Anchorpane.
Looking around I found these two questions where the OP is trying something similar:
JavaFX: FXML: How to make the child to extend its size to fit the parent pane?
JavaFX Panel inside Panel autoresizing
The answers suggest using only the attributes:
 AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0"
inside the child pane. I have tried this with no luck: This is what my code looks like now:
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity"  
         minWidth="-Infinity" prefHeight="792.0" prefWidth="1055.0" 
        xmlns="http://javafx.com/javafx/null" xmlns:fx="http://javafx.com/fxml/1"
   fx:controller="com.judeochalifu.stock_manager.controller.NewSupplierController">
     <children>
        <SplitPane fx:id="splitPlane" dividerPositions="0.5" "orientation="VERTICAL"  
           AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0"  
           AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
           <items>
             <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0" 
               prefWidth="160.0" />
             <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0"  
               prefWidth="160.0" />
           </items>
      </SplitPane>
     </children>
  </AnchorPane>
What am I missing?

