按钮 ClickListener 在 LibGDX 游戏中不起作用

I am developing an Android game using LibGDX. There are 4 buttons in a menu screen, but the ClickListener of these buttons is not working.

// retrieve the custom skin for our 2D widgets
Skin skin = super.getSkin();

// create the table actor and add it to the stage
table = new Table( skin );
table.width = stage.width();
table.height = stage.height();
stage.addActor( table );

// retrieve the table's layout
TableLayout layout = table.getTableLayout();

// register the button "start game"
TextButton startGameButton = new TextButton( "Start game", skin );
startGameButton.addListener( new ClickListener() {
    @Override
    public void clicked(InputEvent event, float x, float y) {
        System.out.println("hiii");
        Assets.load();
        // game.getSoundManager().play( TyrianSound.CLICK );
        game.setScreen( new GameScreen(game) );
    }
} );

layout.register( "startGameButton", startGameButton );

如何激活LibGDX中按钮的ClickListener?

Gdx.input.setInputProcessor(stage);