asp.net web api 开启HttpContext 的Session功能

在Controller里：
public class ValuesController : ApiController
{
// GET api/values
public IEnumerable<string> Get()
{
var context = HttpContext.Current;
context.Session["a"] = "aaa";
return new string[] { "value1", "value2" };

}

// GET api/values/5
public string Get(int id)
{
var ses = HttpContext.Current.Session["a"];
return ses.ToString();
}
}

执行时出报异常，这时要在Global.asax里添加：开启Session功能
public class WebApiApplication : System.Web.HttpApplication
{
public override void Init()
{
this.PostAuthenticateRequest += (sender, e) => HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
base.Init();
}
｝