How to return a list of strings in C#

Question

Can anybody tell me How to store and return List of Strings.

I am asked this Because i have written a function which returns Collection of strings and I want to prepare a COM for that one and need to consume that COM(to get the returned list ) in VC++ where I can extend some functionality using that list of strings. I hope this would be clear.

Solution 1

List<string> or string[] are the best options.

Here is a sample method that returns list of strings :

public static List<string> GetCities()
{
  List<string> cities = new List<string>();
  cities.Add("Istanbul");
  cities.Add("Athens");
  cities.Add("Sofia");
  return cities;
}

Solution 2

You can store a fixed list of strings as an array:

string[] myStrings = {"Hello", "World"};

Or a dynamic list as a List<string>:

List<string> myStrings = new List<string>();
myStrings.Add("Hello");
myStrings.Add("World");

Solution 3

In C# you can simply return List<string>, but you may want to return IEnumerable<string> instead as it allows for lazy evaluation.

Solution 4

There are many ways to represent a list of strings in .NET, List<string> being the slickest. However, you can't return this to COM because:

1. COM doesn't understand .NET Generics

2. FxCop will tell you that it's bad practice to return an internal implementation of something (List) rather than an abstract interface (IList / IEnumerable).

Unless you want to get into really scary Variant SafeArray objects (not recommended), you need to create a 'collection' object so that your COM client can enumerate the strings.

Something like this (not compiled - this is just an example to get you started):

[COMVisible(true)]
public class CollectionOfStrings
{
  IEnumerator<string> m_enum;
  int m_count;

  public CollectionOfStrings(IEnumerable<string> list)
  { 
    m_enum = list.GetEnumerator();
    m_count = list.Count;
  }

  public int HowMany() { return m_count; }

  public bool MoveNext() { return m_enum.MoveNext(); }

  public string GetCurrent() { return m_enum.Current; }
}

(See http://msdn.microsoft.com/en-us/library/bb352856.aspx for more help)

Solution 5

Yesterday you asked how to do this via COM interop! Why the step backward?

How to return a collection of strings from C# to C++ via COM interop

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