Unity3D: Scene Manager (Loading asynchronously)

SceneManager.cs

using UnityEngine;

public class SceneManager : MonoBehaviour {
	
	private const string LOADING_LEVEL_KEY = "Loading Level";
	
	private static AsyncOperation operation;
	
	public float delayBefore = 0.5f;
	
	public float delayAfter = 0.5f;
	
	private float currentProgress = 0f;
	
	private bool finishing = false;
	
	private void Start() {
		Invoke("StartLoadScene", delayBefore);
	}
	
	private void StartLoadScene() {
		StartCoroutine(LoadScene());
	}
	
	private IEnumerator LoadScene() {
		// Finish load scene if there is no level index assigned.
		if (!PlayerPrefs.HasKey(LOADING_LEVEL_KEY)) yield break;
		
		// Get level index from player preferences.
		int levelIndex = PlayerPrefs.GetInt(LOADING_LEVEL_KEY);
		
		// Remove key. We don't need it anymore.
		PlayerPrefs.DeleteKey(LOADING_LEVEL_KEY);
		
		// Start load scene.
		operation = Application.LoadLevelAsync(levelIndex);
		
		// Mark that scene should not be activated by itself. We will handle it.
		operation.allowSceneActivation = false;
		
		// Update current progress for GUI display.
		currentProgress = operation.progress;

		yield return operation;
	}
	
	private void Update() {
		if (operation == null) return;
		if (finishing) return;
		
		if (operation.progress >= 0.9f) {
			currentProgress = 1.0f;
			Invoke("ActivateScene", delayAfter);
			finishing = true;
		}
	}
	
	private void ActivateScene() {
		operation.allowSceneActivation = true;
	}
	
	public static void LoadLevel(int index) {
		PlayerPrefs.SetInt(LOADING_LEVEL_INDEX, index);
		
		// Load scene name "Loading" which contains of object with SceneManager componenet.
		// SceneManager.Start() will triggered.
		Application.LoadLevel("Loading");
	}
	
	// For debug purpose.
	// OnGUI() could make an error. Please kindly remove this method if it doesn't work.
	// In Unity 5.x, this method is deprecated.
	private void OnGUI() {
		if (operation == null) return;
		
		Rect position = new Rect(10f, 10f, Screen.width - 20f, 100f);
		GUI.Label(position, "Progress: " + currentProgress);
	}

}