XmlSerializerInputFormatter is obsolete - ASP.NET Core 2.1

According to the source code, there's a constructor that has not been marked as Obsolete:

public XmlSerializerInputFormatter(MvcOptions options)

This constructor takes an instance of MvcOptions, so you can pass through your existing options argument:

services.AddMvc(options =>
{
    // allow xml format for input
    options.InputFormatters.Add(new XmlSerializerInputFormatter(options));
}) ...

As of ASP.NET Core 3.0, this constructor is the only one available. Those that were marked obsolete have now been removed.

With .NET Core 2.2 or later XmlSerializerInputFormatter should be marked as deprecated.

Instead a of explicitly defining XML serializers as we did before, in the .NET Core 2.2 we can add them simply by calling AddXmlSerializerFormatters() method which will do the job now. Read here why it has been deprecated

Here is how you can do it.

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc(config =>
    {
        config.RespectBrowserAcceptHeader = true;
        config.ReturnHttpNotAcceptable = true;

        config.OutputFormatters.Add(new CsvOutputFormatter());
    }).AddXmlSerializerFormatters().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
}