private void OnJoinButtonClicked()
    {
        Debug.Log("join button clicked");
        GameObject go    = GameObject.Find("ChannelName");
        InputField input = go.GetComponent <InputField>();

        //init AgoraEngine
        if (ReferenceEquals(app, null))
        {
            app = new AgoraInterface();
            app.loadEngine();
        }
        app.joinChannel(input.text);
        SceneManager.sceneLoaded += OnSceneFinishedLoading;
        // SceneManager.LoadScene("ChatScene", LoadSceneMode.Single);
        SceneManager.LoadScene("ChooseRoomScene", LoadSceneMode.Single);
    }