#730 – Check for null Before Iterating Using foreach Statement

The foreach statement allows iterating through all items in a collection.

            List<string> dogs = new List<string>();
            dogs.Add("Kirby");
            dogs.Add("Jack");

            foreach (string s in dogs)
                Console.WriteLine(s);

            Console.WriteLine("=> Done");

730-001

If the collection referenced in the foreach statement is empty, the body of the loop does not execute.  No exception is thrown.

            List<string> dogs = new List<string>();

            foreach (string s in dogs)
                Console.WriteLine(s);

            Console.WriteLine("=> Done");

730-002
If the object that refers to the collection is null, a NullReferenceException is thrown.

            List<string> dogs = null;

            foreach (string s in dogs)
                Console.WriteLine(s);

            Console.WriteLine("=> Done");

730-003
Because of this, it’s good practice to check for null before iterating through a collection in a foreach loop.

            if (dogs != null)
                foreach (string s in dogs)
                    Console.WriteLine(s);
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About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

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