Unity Screen Manager

ScreenManager.cs

using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System.Collections;

// Based on http://docs.unity3d.com/Manual/HOWTO-UIScreenTransition.html tutorial.
public class ScreenManager : MonoBehaviour
{
  #region Constants

  public const string PARAMETER_VISIBILITY = "IsVisible";
  public const string SHOW_ANIMATION = "Show";
  public const string HIDE_ANIMATION = "Hide";

  #endregion

  #region Members

  // First screen to show.
  public Animator initialScreenAnimator;

  // Current screen's animator.
  private Animator currentScreenAnimator;

  // Reference to the transition parameter.
  private int isVisibleParameter;

  // The GameObject Selected before we opened the current Screen.
  // Used when closing a Screen, so we can go back to the button that opened it.
  private GameObject previousSelectedObject;

  #endregion

  #region Timeline

  public void Awake()
  {
    instance = this;
  }

  public void OnEnable()
  {
    // Store a reference to the parameter we use to trigger the transitions.
    isVisibleParameter = Animator.StringToHash(PARAMETER_VISIBILITY);

    // Do nothing if no initial screen provided.
    if (initialScreenAnimator == null)
    {
      return;
    }

    ShowScreen(initialScreenAnimator);
  }

  #endregion

  #region Methods

  // Show the provided screen and change the navigation/selection.
  public void ShowScreen(Animator screenAnimator)
  {
    if (currentScreenAnimator == screenAnimator)
    {
      return;
    }

    // Store the current selected object so we can revert its state
    // when we dismiss this screen later.
    previousSelectedObject = EventSystem.current.currentSelectedGameObject;

    // Activate and move to front.
    screenAnimator.gameObject.SetActive(true);
    screenAnimator.transform.SetAsLastSibling();

    HideCurrentScreen();

    // Start the Show transition.
    currentScreenAnimator = screenAnimator;
    currentScreenAnimator.SetBool(isVisibleParameter, true);

    // Set an object of the new screen as the selection.
    SetSelected(FindFirstEnabledSelectable(screenAnimator.gameObject));
  }

  // Hide the current screen and change the navigation/selection.
  public void HideCurrentScreen()
  {
    if (currentScreenAnimator == null)
    {
      return;
    }

    // Start the Hide animation.
    currentScreenAnimator.SetBool(isVisibleParameter, false);

    // Revert the selection to the previously selected game object.
    SetSelected(previousSelectedObject);

    // Disable the game animator as soon as the animation is over.
    StartCoroutine(DisableScreenAfterAnimation(currentScreenAnimator));

    // No screen open.
    currentScreenAnimator = null;
  }

  // Deactivate the game object as soon as the animation is over.
  private IEnumerator DisableScreenAfterAnimation(Animator hideAnimation)
  {
    var hasReachedHiddenState = false;
    var isOver = true;

    while (!hasReachedHiddenState && isOver)
    {
      if (!hideAnimation.IsInTransition(0))
      {
        hasReachedHiddenState = hideAnimation.GetCurrentAnimatorStateInfo(0).IsName(HIDE_ANIMATION);
      }

      isOver = !hideAnimation.GetBool(isVisibleParameter);

      yield return new WaitForEndOfFrame();
    }

    if (isOver)
    {
      hideAnimation.gameObject.SetActive(false);
    }
  }

  private void SetSelected(GameObject go)
  {
    EventSystem.current.SetSelectedGameObject(go);
  }

  #endregion

  #region Static

  private static ScreenManager instance;

  public static void Show(Animator a)
  {
    if (instance != null)
    {
      instance.ShowScreen(a);
    }
  }

  public static void Hide()
  {
    if (instance != null)
    {
      instance.HideCurrentScreen();
    }
  }

  // Find the first `Selectable` element in the provided hierarchy.
  public static GameObject FindFirstEnabledSelectable(GameObject gameObject)
  {
    GameObject go = null;
    var selectables = gameObject.GetComponentsInChildren<Selectable>(true);
    foreach (var selectable in selectables)
    {
      if (selectable.IsActive() && selectable.IsInteractable())
      {
        go = selectable.gameObject;
        break;
      }
    }

    return go;
  }

  #endregion
}