Libgdx, Why Should I Use Constructors When Switching Screens? - memory-management

Question

I am a beginner in libgdx and was wondering in what cases you would need to use a constructor when switching screens (examples would be helpful). Is it to save memory? Also, is it better to create instances of all the screens in the main class that extends the game?
Here is an example of instances from https://code.google.com/p/libgdx-users/wiki/ScreenAndGameClasses :
public class MyGame extends Game {
MainMenuScreen mainMenuScreen;
AnotherScreen anotherScreen;
#Override
public void create() {
mainMenuScreen = new MainMenuScreen(this);
anotherScreen = new AnotherScreen(this);
setScreen(mainMenuScreen);
}
}
The constructor is in the next class:
public class MainMenuScreen implements Screen {
MyGame game; // Note it's "MyGame" not "Game"
// constructor to keep a reference to the main Game class
public MainMenuScreen(MyGame game){
this.game = game;
}
...

Answer 1

You should avoid creating all screens in Game class in create() method (you will allocate much memory at once and pointlesly). Create only one screen at a time when do you need It. So e.g. you click button New game in menu and there you call game.setScreen(new NextScreen(this));
You do not have to make constructor with Game parameter - but you will not have reference to the main Game class. Having reference to main game class is good for changing screens, method setScreen(screen).

Answer 2

You need the constructor because your changing to a screen that doesnt extend the Game class which is what u need to call setScreen(); Since ur passing the game class to the constructor you can use it to get back to the screen you were at (or another screen) without creating another class that extends Game

Answer 3

I prefer using a singleton.
Something like
public class MyGame extends Game {
private static MyGame myGame;
public static MyGame getInstance() {
if (myGame == null) {
myGame = new MyGame();
}
return myGame;
}
#Override
public void create() {
setScreen(new MainMenuScreen();
}
}
And the example for desktop main class
public class Main {
public static void main(String[] args) {
LwjglApplicationConfiguration cfg = new LwjglApplicationConfiguration();
cfg.width = 800;
cfg.height = 480;
new LwjglApplication(MyGame.getInstance(), cfg);
}
}
Now whenever you need to change your screen use MyGame.getInstance().setScreen(new ScreenName());