异步调用中HttpContext.Current为null解决方法

public HttpContext context 
...{ 
  get ...{ return HttpContext.Current; } 
  set ...{ value = context; } 
} 

public delegate string delegategetResult(HttpContext context); 

protected void Page_Load(object sender, EventArgs e) 
...{ 
  context = HttpContext.Current; 
  delegategetResult dgt = testAsync; 
  IAsyncResult iar = dgt.BeginInvoke(context, null, null); 
  string result = dgt.EndInvoke(iar); 
  Response.Write(result); 
} 

public static string testAsync(HttpContext context) 
...{ 
  if (context.Application["boolTTS"] == null) 
  ...{ 
    Hashtable ht = (Hashtable)context.Application["TTS"]; 
    if (ht == null) 
    ...{ 
      ht = new Hashtable(); 
    } 
    if (ht["A"] == null) 
    ...{ 
      ht.Add("A", "A"); 
    } 
    if (ht["B"] == null) 
    ...{ 
      ht.Add("B", "B"); 
    } 
    context.Application["TTS"] = ht; 
  } 
  Hashtable hts = new Hashtable(); 
  hts = (Hashtable)context.Application["TTS"]; 
  if (hts["A"] != null) 
  ...{ 
    return "恭喜,中大奖呀"; 
  } 
  else 
  ...{ 
    return "我猜你快中奖了"; 
  } 
}