How to shift buttons in the GridPane?

Question

I wanna the buttons B and D will be remained on their places when the A and C will be disappeared, but instead of it there are shifted to the center. How could I shift them back to their places?

     fifty.setOnAction(e->{
            fifty.setDisable(false);
            int counter = 2;
            ArrayList<String> variants = new ArrayList<>(Arrays.asList("a","b","c","d"));
            variants.remove(trueAnswerIndex);
            String variant;
            int n = 2;

            while(counter>0){
                variant = variants.get(randInt(0,n));
                switch(variant){
                    case "a":
                        gridButtons.getChildren().remove(a);
                        variants.remove("a");
                        break;
                    case "b":
                        gridButtons.getChildren().remove(b);
                        variants.remove("b");
                        break;
                    case "c":
                        gridButtons.getChildren().remove(c);
                        variants.remove("c");
                        break;
                    case "d":
                        gridButtons.getChildren().remove(d);
                        variants.remove("d");
                        break;
                }
                counter--;
                n--;
            }
        });

https://i.sstatic.net/pPpC4.jpg

Answer 1

Just disable the visibility of the buttons instead of removing the buttons.

fifty.setOnAction(e->{
        fifty.setDisable(false);
        int counter = 2;
        ArrayList<String> variants = new ArrayList<>(Arrays.asList("a","b","c","d"));
        variants.remove(trueAnswerIndex);
        String variant;
        int n = 2;

        while(counter>0){
            variant = variants.get(randInt(0,n));
            switch(variant){
                case "a":
                    a.setVisible(false);
                    variants.remove("a");
                    break;
                case "b":
                    b.setVisible(false);
                    variants.remove("b");
                    break;
                case "c":
                    c.setVisible(false);
                    variants.remove("c");
                    break;
                case "d":
                    d.setVisible(false);
                    variants.remove("d");
                    break;
            }
            counter--;
            n--;
        }
    });

Answer 2

You can either use some dummy components, like empty Text nodes, or manually set RowConstraints and ColumnConstraints for your GridPane.

The latter is my preferred approach. In the example below I set these constraints for first two rows and columns, so even if the button gets hidden or removed, other columns will not be automatically resized.

I also put the GridPane inside another Node, because otherwise it would fill the whole Scene.

public class JavaFXTest extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {
        Group root = new Group();
        GridPane pane = new GridPane();

        for (int i = 0; i < 2; i++) {
            RowConstraints rc = new RowConstraints();
            rc.setPrefHeight(100);

            ColumnConstraints cc = new ColumnConstraints();
            cc.setPercentWidth(100);

            pane.getRowConstraints().add(rc);
            pane.getColumnConstraints().add(cc);
        }

        Button b1 = new Button("1");
        b1.setPrefSize(100, 100);

        Button b2 = new Button("2");
        b2.setPrefSize(100, 100);

        Button b3 = new Button("3");
        b3.setPrefSize(100, 100);

        Button b4 = new Button("4");
        b4.setPrefSize(100, 100);

        b1.setOnAction(e -> {
            b2.setVisible(false);
        });

        b2.setOnAction(e -> {
            b3.setVisible(false);
        });

        b3.setOnAction(e -> {
            b4.setVisible(false);
        });

        b4.setOnAction(e -> {
            b1.setVisible(false);
        });

        pane.add(b1, 0, 0);
        pane.add(b2, 1, 0);
        pane.add(b3, 0, 1);
        pane.add(b4, 1, 1);

        root.getChildren().add(pane);
        Scene scene = new Scene(root, 400, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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