private void RegisterCallEventNotification() { _callEventCb = (CallEvent callEvent, IntPtr eventData, IntPtr userData) => { _callEvent?.Invoke(null, new CallEventEventArgs(callEvent, CmUtility.GetCallEventData(callEvent, eventData))); }; int ret = Interop.CallManager.SetCallEventCb(_handle, _callEventCb, IntPtr.Zero); if (ret != (int)CmError.None) { Log.Error(CmUtility.LogTag, "Failed to set call event notification callback, Error: " + (CmError)ret); CmUtility.ThrowCmException(ret, _handle); } }