UI vars disappearing after the canvas are re-initialized

Welcome,
I built UI system consisting of several canvas, which I instantiate from Resources folder for every screen of my game, and each of these screens is a separate state of my custom state machine (I instantiate those canvas in my OnActivate() method). All my buttons have their methods assigned from script. Now, it all looks like this:

void InitUI()
{
canvasAboutMenu = (GameObject) Instantiate (Resources.Load("CanvasAboutMenu"));
canvasAboutMenu.SetActive(true);

var buttonBack = GameObject.Find("Button_Back").GetComponent<Button>();
buttonBack.onClick.AddListener(Back);
}

I then switch between canvas using .SetActive(), where needed.

Everything seems to works fine, but just once. I mean, when I visit each screen more than once, clicking on buttons have no effect - as if those variables were somehow lost. Am I doing something wrong?

 

sure, please let me know how to do it.

 

thank you!