[java] JavaFX Panel inside Panel auto resizing

I have a JavaFX application which has only one FXML file. In this file I have one AnchorPane which has a StackPane inside it. Here is the screenshot:

When I start this application, I want to resize StackPane automatically with the AnchorPane. Thus; StackPane will get the current avaliable width and height automatically. At the moment when I resize the application, AnchorPane is being resized automatically but StackPane stays as his fixed size.

How can I resize the StackPane automatically and make it fully stretched inside its parent panel?

My Code

Main.java

package app;

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 {

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

  @Override
  public void start(Stage stage) throws Exception {
      Parent root = FXMLLoader.load(getClass().getResource("Main.fxml"));
      Scene scene = new Scene(root,800,600);
      scene.getStylesheets().add(this.getClass().getResource("/app/style1.css").toExternalForm());
      stage.setScene(scene);
      stage.show();
  }
}

MainController.java

package app;

import java.net.URL;
import java.util.ResourceBundle;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.StackPane;

public class MainController implements Initializable {

   @FXML
   private AnchorPane anchorPane;
   @FXML
   private StackPane stackPane;

   @Override
   public void initialize(URL url, ResourceBundle rb) {
     stackPane.setPrefSize(anchorPane.getPrefWidth(), anchorPane.getPrefHeight()); //didn't work
   }    
}

Main.fxml

<?xml version="1.0" encoding="UTF-8"?>
<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<AnchorPane fx:id="anchorPane" xmlns:fx="http://javafx.com/fxml" fx:controller="app.MainController">
    <StackPane fx:id="stackPane" ></StackPane>
</AnchorPane>

style1.css

#anchorPane { 
    -fx-border-width: 2px;
    -fx-border-color: chartreuse;
}
#stackPane {
    -fx-border-width: 2px;
    -fx-border-color: red;

    /* didn't work */
   -fx-hgap: 100%;
   -fx-vgap: 100%;
}

Also see here

@FXML
private void mnuUserLevel_onClick(ActionEvent event) {
    FXMLLoader loader = new FXMLLoader(getClass().getResource("DBedit.fxml"));
    loader.setController(new DBeditEntityUserlevel());

    try {
           Node n = (Node)loader.load();
           AnchorPane.setTopAnchor(n, 0.0);
           AnchorPane.setRightAnchor(n, 0.0);
           AnchorPane.setLeftAnchor(n, 0.0);
           AnchorPane.setBottomAnchor(n, 0.0);
           mainContent.getChildren().setAll(n);
    } catch (IOException e){
           System.out.println(e.getMessage());
    }
}

The scenario is to load a child fxml into parent AnchorPane. To make the child to stretch in accords to its parent use AnChorPane.setxxxAnchor command.

No need to cede.

just select pane ,right click then select Fit to parent.

It will automatically resize pane to anchor pane size.

If you are using Scene Builder, you will see at the right an accordion panel which normally has got three options ("Properties", "Layout" and "Code"). In the second one ("Layout"), you will see an option called "[parent layout] Constraints" (in your case "AnchorPane Constrainsts").

You should put "0" in the four sides of the element wich represents the parent layout.

It is quite simple because you are using the FXMLBuilder.

Just follow these simple steps:

1. Open FXML file into FXMLBuilder.
2. Select the stack pane.
3. Open the Layout tab [left side tab of FXMLBuilder].
4. Set the sides value by which you want to compute the pane size during stage resize like TOP, LEFT, RIGHT, BOTTOM.

I was designing a GUI in SceneBuilder, trying to make the main container adapt to whatever the window size is. It should always be 100% wide.

This is where you can set these values in SceneBuilder:

Toggling the dotted/red lines will actually just add/remove the attributes that Korki posted in his solution (AnchorPane.topAnchor etc.).