How do I center JavaFX controls

Question

More specifically, why are my JavaFX controls not being centered? Here are two screenshots, the first just after starting (I moved the window into a more visible spot but have not yet resized it), and the second is just after resizing it to show off my problem. Bonus points if you help me ensure it's properly sized (on all DPIs) when it first shows:

Conveniently, the relevant code is included in those screenshots. If you still need it as text, here you go:

private void initJFXPanel(JFXPanel holder)
{
    {
        {
            rootGrid = new GridPane();
            rootGrid.setAlignment(Pos.CENTER);
            rootGrid.setPadding(new Insets(16));
            rootGrid.setHgap(16);
            rootGrid.setVgap(8);
        }

        interior = holder.getScene();
        if (interior == null)
            holder.setScene(interior = new Scene(rootGrid));
        interior.setRoot(rootGrid);

    }
    {
        statusLabel = new Label("Checking for Updates...");
        statusLabel.setAlignment(Pos.CENTER);
        statusLabel.setTextAlignment(TextAlignment.CENTER);
        rootGrid.add(statusLabel, 0, 0);
    }
    {
        progressBar = new ProgressBar();
        progressBar.setProgress(-1);
        progressBar.setPrefWidth(Constants.MAX_WIN_BOUNDS.width / 5d); // 1/5 the width of the screen
        rootGrid.add(progressBar, 0, 1);
    }
    {
        downloadButton = new Button("Get it!");
        downloadButton.setAlignment(Pos.CENTER);
        rootGrid.add(downloadButton, 0, 2);
    }
    holder.setMinimumSize(new Dimension((int)(rootGrid.getPrefWidth() + .5), (int)(rootGrid.getPrefHeight() + .5)));
    setMinimumSize(holder.getMinimumSize());
}

Answer 1

Resize Issue

Make sure you are adding a size to your JFrame

frame.setSize(500, 300);

Center Issue

I am not sure whether you are taking about centering your frame or the JavaFX controls in the GridPane, so I am adding answers for both of them

Frame Screen Centering

Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
frame.setLocation(dim.width/2-frame.getSize().width/2, 
                                        dim.height/2-frame.getSize().height/2);

GridPane Child Centering

You need to add

GridPane.setHalignment(child, HPos.CENTER);

to your code, remove the rest unnecessary code

I edited your code :

{
    Label statusLabel = new Label("Checking for Updates...");
    //statusLabel.setAlignment(Pos.CENTER);
    //statusLabel.setTextAlignment(TextAlignment.CENTER);
    rootGrid.add(statusLabel, 0, 0);
    GridPane.setHalignment(statusLabel, HPos.CENTER);
}
{
    ProgressBar progressBar = new ProgressBar();
    progressBar.setProgress(-1);
    progressBar.setPrefWidth(400); // 1/5 the width of the screen
    rootGrid.add(progressBar, 0, 1);
}
{
    Button downloadButton = new Button("Get it!");
    //downloadButton.setAlignment(Pos.CENTER);
    rootGrid.add(downloadButton, 0, 2);
    GridPane.setHalignment(downloadButton, HPos.CENTER);
}

and the result is

Answer 2

Solution

Place your controls in a VBox (or other similar root layout pane) and set the VBox alignment to center.

Layout Advice

This is my personal advice on starting with layout in JavaFX (it's just advice and not applicable to everybody, you can take it or leave it):

• Your window and all controls and layouts will automatically size to their preferred size.
• Let the in-built layout managers and layout system do as many calculations for you as possible with you just providing the minimum layout hints necessary to get your result.
• Stick to using JavaFX only or Swing only code until you are familar with both styles of code development and really need to mix them.
• Use the SceneBuilder tool to play around with different layouts and get familiar with JavaFX layout mechanisms.
• Study the JavaFX layout tutorial.
• Review a presentation on JavaFX layout.
• To center a stage the screen call stage.centerOnScreen().
• Consider using the built-in dialog support of Java 8u40 (when it is released).

Hi-dpi support

See the answer to:

• JavaFX 8 HiDPI Support

FXML based sample code for your dialog

You can load the following up in SceneBuilder to easily display it:

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

<?import javafx.geometry.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>

<VBox alignment="CENTER" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" spacing="8.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1">
   <children>
      <Label fx:id="updateStatus" text="Checking for Updates..." />
      <ProgressBar fx:id="updateProgress" prefWidth="200.0" progress="0.0" />
      <Button fx:id="updateAction" mnemonicParsing="false" text="Get it!" />
   </children>
   <padding>
      <Insets bottom="16.0" left="16.0" right="16.0" top="16.0" />
   </padding>
</VBox>