Load a level asynchronously in Unity3d

ClickToLoadAsync.cs

//From: http://unity3d.com/learn/tutorials/modules/beginner/live-training-archive/creating-a-scene-menu

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

public class ClickToLoadAsync : MonoBehaviour {
    
    //The slider that is going to be affected
    public Slider loadingBar;
    
    //In the example, this was a full sized black raw Image
    //with the slider and a loading text
    public GameObject loadingImage;

    private AsyncOperation async;
    
    //Call this from a ui button or other script
    public void ClickAsync(int level)
    {
        loadingImage.SetActive(true);
        StartCoroutine(LoadLevelWithBar(level));
    }

    //This will change the scene automatically after
    //having shown the loading screen with progress
    IEnumerator LoadLevelWithBar (int level)
    {
        async = Application.LoadLevelAsync(level);
        while (!async.isDone)
        {
            loadingBar.value = async.progress;
            yield return null;
        }
    }
}