private static extern void NotifyNotificationAddAction(IntPtr notificationPtr, string action, string label, NotifyActionCallback callback, IntPtr opaque, GFreeFunc freeFunc);
public void AddAction <T>(string action, string label, NotifyActionCallback <T> callback, T userData)
{
NotifyNotificationAddAction(_notificationPtr, action, label, NotifyActionCallbackDelegate, GCHandle.ToIntPtr(GCHandle.Alloc(new UserData(callback, userData))), GcHandleFreeFuncDelegate);
}