asked on

Checking object null in c#

Hi Experts,

We have so many instances in our code to check if object is null

public void MethodA(FooA foo)
{

if(foo==null)
{
	throw new ArgumentNullException("foo");

}

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I was told to write extension method to check if object is null and call this method everywhere and have written following code for this with parameters object and string

public static class ExtesnionObjectHelper
        { 
           public static void VerifyNotNull(this Object targetObject,string message)
          {
              if (targetObject == null)
              {
                  throw new ArgumentNullException(message);
              }
          }
        }

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In the above MethodA now I can simply call like this foo.VerifyNotNull("foo").

I am little bit confused and have following scenarios and could anyone correct me if I can call the extension method like above for all below scenarios .

1)[b]IEnumerable dates[/b]
public void MethodB(IEnumerable<DateTime> dates)
{
if(dates==null)
{
	throw new ArgumentNullException("dates");
}
dates.VerifyNotNull("dates");  // correct or  wrong
}

2)[b] IList of ids[/b]
public void MethodC(IList<int64> ids
{

if(ids==null)
{
	throw new ArgumentNullException(ids);
}

ids.VerifyNotNull("ids");  // correct or  wrong
}

3)[b]string[/b]
public void MethodD(string username)
{
if(string.IsNullOrEmpty(username)
{
	throw new ArgumentNullException("username");
}
username.VerifyNotNull("username"); // correct or  wrong

4)[b]Enum value[/b]

public void MethodE(this Enum value)
{
if(value==null)
{
	throw new ArgumentNullException("value");
}
value.VerifyNotNull("value");  // correct or  wrong
 }

5)[b]Generic IList<T>[/b]
public void MethodF(IList<TEntity>> action)
{
if(action==null)
{
	throw new ArgumentNullException("action");
}
action.VerifyNotNull("action"); // correct or  wrong
}

6)I[b]Enumerable validationResult[/b]

public void MethodG(IEnumerable<validationResult> results)
{
if(results==null)
{
	throw new ArgumentNullException("results");
}
results.VerifyNotNull("results");  // correct or  wrong
}

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Thanks in Advance

ASKER CERTIFIED SOLUTION

Éric Moreau

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ste5an

Use Contracts.

ksd123

ASKER

Eric,

Apart from Enum , can I use IList of ids (int) and IEnumerable of dates as well ?

SOLUTION

kaufmed

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kaufmed

P.S.

Just be careful with this approach. I tried the same exact thing a couple of years back, and when I showed it to my boss, he claimed it made the code less readable. His point was that, prior to the introduction of extension methods, it would never make sense that an object would be able to call a method that verifies that same object is not null--the object doesn't even exist if it's null, so how could it have methods? Functionally speaking, the approach works, but if your teammates don't understand how it works, then you've introduced ambiguity into your code.

Vikram Singh Saini

I had to agree with käµfm³d.

Someone don't want you to use advance stuff for interest of developers not knowing about that. Because in your absence it might worry them as it will be hard for them to get to root. :)

ste5an

As I said, use contracts.

When this is too advanced, simply create your own Contract class with you static method and signature. Then it is transparent what it does.

btw, this would also allow that you add simple parameter checks to this class with the same behaviour (raising exceptions). Even you can use more complex tests when you pass lambda expressions to it.

E.g.

namespace ConsoleCS
{
    using System;
    using System.Collections.Generic;
    using System.Linq;

    class Contract
    {
        public static void EnsureArgumentIsNotNull(object argument, string message)
        {
            if (argument == null)
            {
                throw new ArgumentNullException(message);
            }
        }

        public static void EnsureArgumentListIsNotEmpty<T>(IEnumerable<T> argumentList, string message)
        {
            Contract.EnsureArgumentIsNotNull(argumentList, message);
            bool result = (argumentList.Count() == 0);
            if (!result)
            {
                foreach (T value in argumentList)
                {
                    if (value == null)
                    {
                        result = true;
                        break;
                    }
                }
            }

            if (result)
            {
                throw new ArgumentException(message);
            }
        }
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            List<int> intList = new List<int>();
            List<object> objectList = new List<object>();

            Console.WriteLine("MethodB(null)");
            try { MethodB(null); } 
            catch (Exception ex) { Console.WriteLine(ex.Message); }

            Console.WriteLine("\nMethodC(null)"); 
            try { MethodC(null); }
            catch (Exception ex) { Console.WriteLine(ex.Message); }

            Console.WriteLine("\nMethodD(null)"); 
            try { MethodD(null); }
            catch (Exception ex) { Console.WriteLine(ex.Message); }

            Console.WriteLine("\nMethodF(intList)");
            try { MethodF(intList); }
            catch (Exception ex) { Console.WriteLine(ex.Message); }

            intList.Add(1);
            Console.WriteLine("\nMethodF(intList)");
            try { MethodF(intList); }
            catch (Exception ex) { Console.WriteLine(ex.Message); }

            Console.WriteLine("\nMethodG(objectList)");
            try { MethodG(objectList); }
            catch (Exception ex) { Console.WriteLine(ex.Message); }

            objectList.Add(null);
            Console.WriteLine("\nMethodG(objectList)");
            try { MethodG(objectList); }
            catch (Exception ex) { Console.WriteLine(ex.Message); }

            Console.WriteLine("\nDone.");
            Console.ReadLine();
        }

        static void MethodB(IEnumerable<DateTime> dates)
        {
            Contract.EnsureArgumentIsNotNull(dates, "Argument dates must not be null."); 
        }

        static void MethodC(IList<int> ids)
        {         
            Contract.EnsureArgumentIsNotNull(ids, "Argument ids must not be null."); 
        }

        static void MethodD(string username)
        {            
            Contract.EnsureArgumentIsNotNull(username, "Argument username must not be null."); 
        }

        static void MethodF(IList<int> ids)
        {
            Contract.EnsureArgumentListIsNotEmpty(ids, "Argument ids must not be null or empty.");
        }

        static void MethodG(IList<object> ids)
        {
            Contract.EnsureArgumentListIsNotEmpty(ids, "Argument ids must not be null or empty.");
        }
    }
}

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ksd123

ASKER

Thank you all