Opc.Ua.Server.MonitoredItem.ValueChanged C# (CSharp) Method

        public static bool ValueChanged(
            DataValue value,
            ServiceResult error,
            DataValue lastValue,
            ServiceResult lastError, 
            DataChangeFilter filter,
            double range)
        {
            if (value == null) throw new ArgumentNullException("value");

            // select default data change filters.
            double deadband = 0.0;
            DeadbandType deadbandType = DeadbandType.None;
            DataChangeTrigger trigger = DataChangeTrigger.StatusValue;

            // apply filter.
            if (filter != null)
            {
                trigger = filter.Trigger;
                deadbandType = (DeadbandType)(int)filter.DeadbandType;
                deadband = filter.DeadbandValue;

                // when deadband is used and the trigger is StatusValueTimestamp, then it should behave as if trigger is StatusValue.
                if ((deadbandType != DeadbandType.None) && (trigger == DataChangeTrigger.StatusValueTimestamp))
                {
                    trigger = DataChangeTrigger.StatusValue;
                }
            }
            
            // get the current status.
            uint status = StatusCodes.Good;
            
            if (error != null)
            {
                status = error.StatusCode.Code;
            }
            else if (lastValue != null)
            {
                status = value.StatusCode.Code;
            }

            // get the last status.
            uint lastStatus = StatusCodes.Good;

            if (lastError != null)
            {
                lastStatus = lastError.StatusCode.Code;
            }
            else if (lastValue != null)
            {
                lastStatus = lastValue.StatusCode.Code;
            }

            // value changed if any status change occurrs.
            if (status != lastStatus)
            {
                return true;
            }

            // value changed if only one is null.
            if (value == null || lastValue == null)
            {
                return lastValue != null || value != null;
            }

            // check if timestamp has changed.
            if (trigger == DataChangeTrigger.StatusValueTimestamp)
            {
                if (lastValue.SourceTimestamp != value.SourceTimestamp)
                {
                    return true;
                }
            }

            // check if value changes are ignored.
            if (trigger == DataChangeTrigger.Status)
            {
                return false;
            }

            // check if reference to same object.
            if (!Equals(lastValue.Value, value.Value, deadbandType, deadband, range))
            {
                return true;
            }

            // must be equal.
            return false;
        }