private IEnumerator LoadCoroutine(WWWLoadCallback callback)
    {
        www = new WWW(pathname);
        yield return www;

        if (!string.IsNullOrEmpty(www.error))
        {
            callback(null);
        }
        else
        {
            callback(www);
        }
    }
 public void StartLoad(WWWLoadCallback callback)
 {
     BundleLoader.pInstance.StartCoroutine(LoadCoroutine(callback));
 }