How to get MsBuildWorkSpace in IVsSingleFileGenerator?

I want to create a C# fileGenerator,so i dowload the samples and learn from video.

https://channel9.msdn.com/Blogs/MVP-Windows-Dev/Learn-Roslyn-Now-E06-MSBuildWorkspace

But when I use GetService method to get workspace,it returns null.

public class NFinalControllerGenerator :BaseCodeGeneratorWithSite
    {
        public VisualStudioWorkspace visualStuioWorkspace = null;
        internal static string name = "NFinalControllerGenerator";
        protected override byte[] GenerateCode(string inputFileContent)
        {

            var componentModel = (IComponentModel)this.GetServiceObject(typeof(SComponentModel));
            if (componentModel != null)
            {
                visualStuioWorkspace = componentModel.GetService<Microsoft.VisualStudio.LanguageServices.VisualStudioWorkspace>();
            }
            return System.Text.Encoding.UTF8.GetBytes("Hello World!");
        }
     }

It's something wrong?

My goal is to Generate serveral new C# class from old file, that has all Fields and Propertys.