> .NET Intermediate Topics > Reflection > Library Version Issues

Library Version Issues

Have you ever ran into an error message like this but the version you have is newer than the one shown?

'Could not load file or assembly 'Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The system cannot find the file specified.'

You can fix it by adding a callback that is invoked when the system can’t find the exact version of the library.

The code

In this example, I am targeting .NET Framework 4.7.2 and the nuget package that I’ve imported has a dependency on an older version of Json.NET and throws an error, however I need the newest version of Json.NET (I can’t have 2 versions in the same project), so I’m going to tell the runtime to just use the newer assembly that I have.

void Main(string[] args){
	//add these two lines as well as the MyResolveEventHandler below
	AppDomain currentDomain = AppDomain.CurrentDomain;
    currentDomain.AssemblyResolve += new ResolveEventHandler(MyResolveEventHandler);

	//this is the code that was throwing the exception
	HttpClient client = new HttpClient();
	client.BaseAddress = new System.Uri( "http://localhost");
	var response = client.PostAsJsonAsync("/whatever/api", "whatever").Result;	//this call will cause the FileNotFoundException because the nuget lib that implements PostAsJsonAsync references 6.0.0.0
}

private static System.Reflection.Assembly MyResolveEventHandler(object sender, ResolveEventArgs args)
{
	if(args.Name.StartsWith("Newtonsoft.Json")) {
		//you can pick any class that is in the Newtonsoft.Json.dll
		return typeof(Newtonsoft.Json.JsonConverter).Assembly;
	}
	return null;
}

Note that using the newer version of the dll may not always work, in which case you can also load the assembly by file path.

return System.Reflection.Assembly.LoadFrom($@"C:\somepath\to\your.dll");

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