How can I make a Canvas automatically resize to fit its parent in JavaFX?

Automatically Resizing Canvas to Fit the Enclosing Parent

Resizing a Canvas to match its enclosing parent's dimensions is essential for dynamic user interfaces. JavaFX provides several approaches to achieve this, one of which is using a nested class that overrides the layoutChildren() method.

Approach Using CanvasPane

The CanvasPane class is a custom Pane that wraps a Canvas and ensures the Canvas's dimensions always match the enclosing Pane's size. Create an instance of CanvasPane, passing the desired initial Canvas dimensions as arguments. By overriding the layoutChildren() method, CanvasPane's layout algorithm automatically adjusts the Canvas's position and size to fill the available space.

Example Code

<code class="java">public class CanvasPane extends Pane {

    private final Canvas canvas;

    public CanvasPane(double width, double height) {
        canvas = new Canvas(width, height);
        getChildren().add(canvas);
    }

    public Canvas getCanvas() {
        return canvas;
    }

    @Override
    protected void layoutChildren() {
        super.layoutChildren();
        // Retrieve the enclosing Pane's dimensions after layout calculations
        double x = snappedLeftInset();
        double y = snappedTopInset();
        double w = snapSize(getWidth()) - x - snappedRightInset();
        double h = snapSize(getHeight()) - y - snappedBottomInset();
        
        // Update the Canvas's layout and dimensions
        canvas.setLayoutX(x);
        canvas.setLayoutY(y);
        canvas.setWidth(w);
        canvas.setHeight(h);
    }
}</code>

Binding to Parent

In the code snippet provided, the Canvas is added to a CanvasPane, which is then added to a Stage. The CanvasPane is bound to the Stage's dimensions using CSS3 binding, thus ensuring that the Canvas always fills the Stage's available space.

Utilizing Java 9 Snap Functions

The provided JavaFX 8 code includes deprecated snapSize() and isResizable() methods. In Java 9 and later, use snapSizeX() and snapSizeY() to retrieve preferred sizes and leverage bind(Observable[]) to achieve similar functionality.

By employing this approach, your Canvas will automatically resize itself to match the parent node's dimensions, providing a more responsive and flexible user interface.

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