Defensive programming – simple method to prevent Object reference not set exception

 

Just to share a simple way to prevent the ugly “object reference not set” exception: 

public class DefensiveCode
    {
        //Non-defensive code (unsafe):
        public IList<string> UnsafeProps { get; set; }
        public void DoSomething(string input)
        {
            //props can be null --> exception
            if (UnsafeProps.Contains(input))
            {
                //....do work
            }
        }

        //Defensive code #1:
        public IList<string> SafeProps { get; set; }
        public void DoSomethingSafely(string input)
        {
            //a little better, but have to check every time
            //and it may depend on how compiler evaluate: L-to-R is OK, but R-to-L will not be OK
            if (SafeProps != null && SafeProps.Contains(input))
            {
                //....do work
            }
        }


        //Defensive code #2: (preferred)
        private IList<string> _SafestProps;
        public IList<string> SafestProps
        {
            get
            {
                //initialize before accessing it. 
                if (_SafestProps == null) _SafestProps = new List<string>();
                return _SafestProps;
            }
            set { _SafestProps = value; }
        }

        public void DoSomethingSafestWay(string input)
        {
            //it’s always safe
            if (SafestProps.Contains(input))
            {
                //....do work
            }
        }
    }

A lesson learnt: do not return NULL , return empty list or empty string instead.