C# Create an instance of a class from a type FullName

Question

Does anybody know of an easy way to create an instance of a class given the FullName of a type (namespace.classname format), but not having the AssemblyQualifiedName? The FullName of the type is only contained in a single assembly that is referenced and available at runtime, so there is no ambiguity.

I don't have the type, I have a string - the fullname only, without the assembly part. I don't know the assembly, I just know it's referenced and there is only one assembly containing the type fullname.

Thanks!

EDIT: This is to do with deserialization of instances from a proprietary protocol. I've recieved good answers, but what I'll end up do in order to have optimal solution and not iterate through all the assemblies is to create a static dictionary with fullName key and assembly qualified name as value, given I know which exactly are the classes and they are a limited set.

If you can get the `Assembly` object (perhaps via `typeof(SomeKnownType).Assembly`), you can use `thatAssembly.GetType(fullName)` ? — Marc Gravell, May 14 '19 at 15:59
@ Marc Gravell no, I don't have the type, I have a string - the fullname only, without the assembly part. I don't know the assembly, I just know it's referenced and there is only one assembly containing the type fullname. — vezenkov, May 14 '19 at 16:02
If your assembly is already referenced in your project, you don't need the Assembly Qualified Name. — Robert Harvey, May 14 '19 at 16:04
in the comment above, I only used the `fullName`. The `SomeKnownType` was just **any other type** from that assembly, as a lazy mechanism of getting the `Assembly` instance — Marc Gravell, May 14 '19 at 16:04
Have you take a look on [AssemblyResolve event](https://learn.microsoft.com/en-us/dotnet/api/system.appdomain.assemblyresolve?view=netframework-4.8) to resolve the missing assembly name? — Troopers, May 14 '19 at 16:10
@ Robert Harvey I don't know the assembly - might be few of the assemblies - I get only the fullName of the type from the protocol. So the only option is to iterate through the assemblies or define a static dictionary and use it at runtime to find the assembly. If you know a more convenient way, please post it as an answer, I'll accept it. — vezenkov, May 14 '19 at 21:16

score 3 · Answer 1 · answered May 14 '19 at 16:07

3

You can get all of the active assemblies and then look through each one for a type with the full name you have. You'll need to prepare for the possibility that there are multiple matches, or no matches, among the assemblies.

answered May 14 '19 at 16:07

Servy

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This is what I am trying to avoid doing. It's to do with several assemblies and types that are referenced for sure (proprietary) where these are being deserialized and recreated as instances. What I am thinking as an alternative is to create a static dictionary with fullName key and assembly qualified name as value. – vezenkov May 14 '19 at 20:59

John Wu · Accepted Answer · 2019-05-14T16:25:37.960

0

Load all of your assemblies and select over their types, then filter on the name.

public static object CreateType(string typeName)
{
    var allTypes = AppDomain.CurrentDomain
        .GetAssemblies()
        .SelectMany
        (
            a => a.GetTypes()
        );
    var type = allTypes.Single( t => t.Name == typeName );

    return Activator.CreateInstance(type);
}

You might consider adding some validation code to check for duplicates, and to ensure there is a default constructor.

edited May 14 '19 at 16:25

answered May 14 '19 at 16:19

John Wu

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Good - it's a way to do it and I mark it as an answer (provided the code), maybe slow if many assemblies and types, but that's it. I'd check for "&& t.IsClass && !t.IsInterface && !t.IsAbstract" to be sure CreateInstance will work - although in my particular case it will work without this check. – vezenkov May 14 '19 at 21:29

C# Create an instance of a class from a type FullName

2 Answers2