Check for null in foreach loop

user_531984 0
Viewed 108321

Is there a nicer way of doing the following:
I need a check for null to happen on file.Headers before proceeding with the loop 

if (file.Headers != null)
{
  foreach (var h in file.Headers)
  {
   //set lots of properties & some other stuff
  }
}

In short it looks a bit ugly to write the foreach inside the if due to the level of indentation happening in my code.

Is something that would evaluate to 

foreach(var h in (file.Headers != null))
{
  //do stuff
}

possible?

null foreach loops c#
8 Answers

The best answer in the year 2022 should be:

foreach (var h in file.Headers ?? Enumerable.Empty<T>())
{
    //do stuff
}

Replace T with your data type. if file.Headers is an array, use Array.Empty<T>() instead of Enumerable.Empty<T>()

user_147238980

For some cases I'd prefer slightly another, generic variant, assuming that, as a rule, default collection constructors return empty instances.

It would be better to name this method NewIfDefault. It can be useful not only for collections, so type constraint IEnumerable<T> is maybe redundant.

public static TCollection EmptyIfDefault<TCollection, T>(this TCollection collection)
        where TCollection: class, IEnumerable<T>, new()
    {
        return collection ?? new TCollection();
    }
user_55981940
Related