How to stop an Item from being deleted with ItemDeleting RER?

Question

I created an Event Receiver that prevents an item if a checkbox is ticked however if I add the condition, the event receiver do not fire

public SPRemoteEventResult ProcessEvent(SPRemoteEventProperties properties)
        {
            using (ClientContext clientContext = TokenHelper.CreateRemoteEventReceiverClientContext(properties))
            {
                SPRemoteEventResult result = new SPRemoteEventResult();
                if (properties.EventType == SPRemoteEventType.ItemDeleting)
                {
                    List list = clientContext.Web.Lists.GetByTitle(properties.ItemEventProperties.ListTitle);
                    ListItem fieldItem = list.GetItemById(properties.ItemEventProperties.ListItemId);

                    if ((bool)fieldItem["CheckBox"])
                    {
                        result.Status = SPRemoteEventServiceStatus.CancelWithError;
                        result.ErrorMessage = "Error";
                    }

                        result.Status = SPRemoteEventServiceStatus.Continue;

                }
                return result;
            }
        }

Answer 1

Call Load and ExecuteQuery Before accessing item properties.

List list = clientContext.Web.Lists.GetByTitle(properties.ItemEventProperties.ListTitle);
ListItem fieldItem = list.GetItemById(properties.ItemEventProperties.ListItemId);

clientContext.Load(fieldItem);
clientContext.ExecuteQuery();

if((bool)fieldItem["CheckBox"]){
  //....
}

Answer 2

You can add properties.Cancel = true; to cancel item from deleting.

public SPRemoteEventResult ProcessEvent(SPRemoteEventProperties properties)
    {
        using (ClientContext clientContext = TokenHelper.CreateRemoteEventReceiverClientContext(properties))
        {
            SPRemoteEventResult result = new SPRemoteEventResult();
            if (properties.EventType == SPRemoteEventType.ItemDeleting)
            {
                List list = clientContext.Web.Lists.GetByTitle(properties.ItemEventProperties.ListTitle);
                ListItem fieldItem = list.GetItemById(properties.ItemEventProperties.ListItemId);

                if ((bool)fieldItem["CheckBox"])
                {
                    result.Status = SPRemoteEventServiceStatus.CancelWithError;
                    result.ErrorMessage = "Error";
                    properties.Cancel = true;
                }

                    result.Status = SPRemoteEventServiceStatus.Continue;

            }
            return result;
        }
    }