private void leaveButtonC()
 {
     if (!ReferenceEquals(app, null))
     {
         app.leaveChannel();
         app.unloadEngine();
         app = null;
         SceneManager.LoadScene("startupScene", LoadSceneMode.Single);
     }
 }
    private void joinButtonC()
    {
        GameObject cNameGO = GameObject.Find("channelName");
        InputField input   = cNameGO.GetComponent <InputField>();

        if (ReferenceEquals(app, null))
        {
            app = new agoraInterface();
            app.loadEngine();
        }

        app.joinChannel(input.text);
        SceneManager.LoadScene("chatRoom", LoadSceneMode.Single);
    }