Detect if the type of an object is a type defined by .NET Framework

Question

How can I determine by reflection if the type of an object is defined by a class in my own assembly or by the .NET Framework?

I dont want to supply the name of my own assembly in code, because it should work with any assembly and namespace.

Minor point - but it could be neither your own nor Microsoft... — Marc Gravell, Jun 07 '09 at 21:53

Jon Skeet · Accepted Answer · 2009-06-07T20:59:46.767

Where would third-party types come in? You might want to differentiate between types which claim to be provided by Microsoft and types which don't.

using System;
using System.Linq;
using System.Reflection;

class Test
{
    static void Main()
    {
        Console.WriteLine(IsMicrosoftType(typeof(string)));
        Console.WriteLine(IsMicrosoftType(typeof(Test)));
    }

    static bool IsMicrosoftType(Type type)
    {
        object[] attrs = type.Assembly.GetCustomAttributes
            (typeof(AssemblyCompanyAttribute), false);

        return attrs.OfType<AssemblyCompanyAttribute>()
                    .Any(attr => attr.Company == "Microsoft Corporation");
    }
}

Of course, any type could claim to be a Microsoft one given this scheme, but if you're actually only going to call it on your own types and framework ones, I suspect this should work fine.

Alternatively, you could use the assembly's public key token. This is likely to be harder to fake. It relies on Microsoft using a common public key for all their assemblies, which they don't (according to Mehrdad's comment below). However, you could easily adapt this solution for a set of accepted "this is from Microsoft" public keys. Perhaps combine the two approaches somehow and report any differences for further inspection...

static bool IsMicrosoftType(Type type)
{
    AssemblyName name = type.Assembly.GetName();
    byte[] publicKeyToken = name.GetPublicKeyToken();

    return publicKeyToken != null
        && publicKeyToken.Length == 8
        && publicKeyToken[0] == 0xb7
        && publicKeyToken[1] == 0x7a
        && publicKeyToken[2] == 0x5c
        && publicKeyToken[3] == 0x56
        && publicKeyToken[4] == 0x19
        && publicKeyToken[5] == 0x34
        && publicKeyToken[6] == 0xe0
        && publicKeyToken[7] == 0x89;
}

Not all Microsoft assemblies have the same public key token (even now). — Mehrdad Afshari, Jun 07 '09 at 20:35
can't convert the byte[] publicKeyToken to string using AsciiEncoding or UnicodeEncoding What encoding is used or how to get a string representation of the PublicKeyToken — Kumar, Aug 04 '09 at 13:53
If you wanted to do a string compare between the BitConverter version and an assemblies full name, you'll need to add the following, or equivalent, as BitConverter formats the value differently: BitConverter.ToString(asmName.GetPublicKeyToken()).Replace("-","").ToLower() — Nathan, Sep 10 '09 at 14:23

score 12 · Answer 2 · answered Aug 04 '09 at 02:07

Based on Jon's answer and Mehrdad's comment, it appears that the following three values are used for the public key token (from AssemblyName.FullName) for the .NET Framework provided assemblies from .NET 2.0 and later:

PublicKeyToken=b77a5c561934e089

mscorlib
System.Data
System.Data.OracleClient
System.Data.SqlXml
System
System.Runtime.Remoting
System.Transactions
System.Windows.Forms
System.Xml
SMDiagnostics
System.Runtime.Serialization
System.ServiceModel
System.ServiceModel.Install
System.ServiceModel.WasHosting

PublicKeyToken=b03f5f7f11d50a3a

Accessibility
AspNetMMCExt
cscompmgd
CustomMarshalers
IEExecRemote
IEHost
IIEHost
ISymWrapper
Microsoft.Build.Conversion
Microsoft.Build.Engine
Microsoft.Build.Framework
Microsoft.Build.Tasks
Microsoft.Build.Utilities
Microsoft.JScript
Microsoft.VisualBasic.Compatibility.Data
Microsoft.VisualBasic.Compatibility
Microsoft.VisualBasic
Microsoft.VisualBasic.Vsa
Microsoft.VisualC
Microsoft.Vsa
Microsoft.Vsa.Vb.CodeDOMProcessor
Microsoft_VsaVb
sysglobl
System.Configuration
System.Configuration.Install
System.Deployment
System.Design
System.DirectoryServices
System.DirectoryServices.Protocols
System.Drawing.Design
System.Drawing
System.EnterpriseServices
System.Management
System.Messaging
System.Runtime.Serialization.Formatters.Soap
System.Security
System.ServiceProcess
System.Web
System.Web.Mobile
System.Web.RegularExpressions
System.Web.Services
Microsoft.Transactions.Bridge
Microsoft.Transactions.Bridge.Dtc
Microsoft.Build.Tasks.v3.5
Microsoft.CompactFramework.Build.Tasks
Microsoft.Data.Entity.Build.Tasks
Microsoft.VisualC.STLCLR
Sentinel.v3.5Client

PublicKeyToken=31bf3856ad364e35

PresentationCFFRasterizer
PresentationUI

This was generated from the following code:

    private void PrintAssemblyInfo(string fullName)
    {
        string[] parts = fullName.Split(',');
        Console.WriteLine(" - {0}, {1}", parts[0], parts[3]);
    }

    private void GenerateInfo(string path)
    {
        foreach (var file in Directory.GetFiles(path, 
           "*.dll",
           SearchOption.AllDirectories))
        {
            try
            {
                Assembly assembly = Assembly.ReflectionOnlyLoadFrom(file);
                PrintAssemblyInfo(assembly.GetName().FullName);
            }
            catch { }
        }
    }

    private void GenerateInfo()
    {
        GenerateInfo(@"C:\Windows\Microsoft.NET\Framework\v2.0.50727");
        GenerateInfo(@"C:\Windows\Microsoft.NET\Framework\v3.0");
        GenerateInfo(@"C:\Windows\Microsoft.NET\Framework\v3.5");
    }

Slightly more modern alternative: https://gist.github.com/OmerRaviv/81c870f0d521e1122e88be4499b74b8c — Omer Raviv, Dec 11 '22 at 20:54

score 8 · Answer 3 · answered Jun 07 '09 at 19:48

8

Similar to Mehrdad's answer, but allows for the same check even if the code is executing in some other application.

obj.GetType().Assembly == typeof(SomeTypeYouKnowIsInYourAssembly).Assembly

answered Jun 07 '09 at 19:48

AgileJon

53,070
5
41
38

score 7 · Answer 4 · answered Jun 07 '09 at 19:41

7

obj.GetType().Assembly == System.Reflection.Assembly.GetExecutingAssembly()

Checks if the type is declared in the current assembly.

answered Jun 07 '09 at 19:41

Mehrdad Afshari

414,610
91
852
789

score 0 · Answer 5 · answered Nov 22 '22 at 12:58

Here is a more modern, circa 2022 version of Scott Dorman's solution, that gives you the final list of public key tokens:

using System.Reflection;

new PublicKeyExplorer().GenerateInfo();

class PublicKeyExplorer
{
private string GetPublicKeyToken(string fullName)
{
    string[] parts = fullName.Split(',');
    return parts[3];
}

private void GenerateInfo(string path, HashSet<string> tokens)
{
    foreach (var file in Directory.GetFiles(path,
                 "*.dll",
                 SearchOption.AllDirectories))
    {
        try
        {
            Assembly assembly = Assembly.LoadFrom(file);
            tokens.Add(GetPublicKeyToken(assembly.GetName().FullName));
        }
        catch (Exception e)
        {
        }
    }
}

public void GenerateInfo()
{
    var tokens = new HashSet<string>();
    GenerateInfo(@"C:\Program Files\dotnet\sdk\3.1.425\", tokens);
    GenerateInfo(@"C:\Program Files\dotnet\sdk\5.0.408\", tokens);
    GenerateInfo(@"C:\Program Files\dotnet\sdk\6.0.401\", tokens);
    GenerateInfo(@"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.8\", tokens);
    GenerateInfo(@"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.6.1\", tokens);

    foreach (var publicKeyToken in tokens)
    {
        Console.WriteLine(publicKeyToken);
    }
}

}

Detect if the type of an object is a type defined by .NET Framework

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