Getting a fully qualified type name from a string .Net C#

Question

I have a string such as "Int", "Double", "DateTime" etc. How do I get the fully qualified name from this string?

Answer 1

It's worth bearing in mind that int isn't a type. It's an alias provided by C# for the type System.Int32. Bearing that in mind, and assuming you only care about core types, you can try:

var typeName = "DateTime";

var systemTypesAssembly = Assembly.Load("mscorlib");

var type = (from t in systemTypesAssembly.GetTypes()
           where t.Name == typeName
           select t).FirstOrDefault();

Console.WriteLine(type.FullName);

As I said, this will not work for Int, but would work for Int32 which is the type it's aliased to. This code also contains no error handling for where, for example, no type is found in mscorlib that matches the one you've entered in typeName

Answer 2

Before I go any further, I'd like to point that there is no class in the .NET Framework base class library named Int. There is System.Int32, that in C# happens to have an alias: int.

You can do this several ways.

A simple but limited way to do this is to have a dictionary mapping strings to the corresponding FQNs:

public static IDictionary<string, string> FqnMap = new Dictionary<string, string>
{
    { "Int", "System.Int32" },
    { "Double", "System.Double" },
    { "DateTime", "System.DateTime" },
};

public string GetFqn(string name)
{
    return FqnMap[name]; // TODO: add error handling
}

A more complex but powerful way would involve using reflection to search all types from a set of assemblies. Something like this:

public class FqnResolver
{
    public FqnResolver(IEnumerable<Assembly> assemblies)
    {
        Assemblies = new List<Assembly>(assemblies);
    }
    public FqnResolver(params Assembly[] assemblies) : this(assemblies as IEnumerable<Assembly>) { }
    public FqnResolver() : this(new Assembly[0]) { }

    public ICollection<Assembly> Assemblies { get; private set; }

    public string GetFqn(string name)
    {
        var candidates = from a in Assemblies
                         from t in a.GetTypes()
                         where t.Name == name
                         select t.FullName;
        return candidates.First(); // will throw if no valid type was found
                                   // and does not count duplicates
    }
}