how to update assemblyBinding section in config file at runtime?

Question

I'm trying to change assembly binding (from one version to another) dynamically.

I've tried this code but it doesn't work:

      Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
      ConfigurationSection assemblyBindingSection = config.Sections["assemblyBinding"];

      assemblyBindingSection.SectionInformation.ConfigSource = "bindingConf.xml";
      config.Save(ConfigurationSaveMode.Modified);

      ConfigurationManager.RefreshSection("assemblyBinding");

with bindingConf.xml containing the assemblyBinding section configuration.

So can a change this section at runtime? how to do it? What alternatives do I have?

Answer 1

I love Eric's answer. It's a lifesaver when trying to use the new buggy NuGet PackageReference model with a Web app. The problem is that you can have msbuild automatically generate the bindings, however, they generate the bindings to Assembly.dll.config, and not to web.config. So this workaround is great.

I've modified Eric's code a bit to make it more generic and work with an ASP.Net Core app:

AppDomain.CurrentDomain.AssemblyResolve += delegate (object sender2, ResolveEventArgs e2)
            {
                var requestedNameAssembly = new AssemblyName(e2.Name);
                var requestedName = requestedNameAssembly.Name;
                if (requestedName.EndsWith(".resources")) return null;
                var binFolder = System.Web.Hosting.HostingEnvironment.MapPath("~/bin");
                var fullPath = Path.Combine(binFolder, requestedName) + ".dll";
                if (File.Exists(fullPath))
                {
                    return Assembly.LoadFrom(fullPath);
                }

                return null;
            };

Answer 2

The best way I've found to dynamically bind to a different version of an assembly is to hook the AppDomain.AssemblyResolve event. This event is fired whenever the runtime is unable to locate the exact assembly that the application was linked against, and it allows you to provide another assembly, that you load yourself, in its place (as long as it is compatible).

For example, you can put in a static constructor on your application's main class that hooks the event like this:

using System.Reflection;

static Program()
{
    AppDomain.CurrentDomain.AssemblyResolve += delegate(object sender, ResolveEventArgs e)
    {
        AssemblyName requestedName = new AssemblyName(e.Name);

        if (requestedName.Name == "AssemblyNameToRedirect")
        {
            // Put code here to load whatever version of the assembly you actually have

            return Assembly.LoadFrom("RedirectedAssembly.DLL");
        }
        else
        {
            return null;
        }
    };
}

This method avoids the need to deal with the assembly bindings in configuration files and is a bit more flexible in terms of what you can do with it.