字典TryGetValue NullReferenceException

Question

我在线上得到NullReferenceException _dicCache.TryGetValue(objID, out newObject); .我不知道为什么会发生这种情况.可以告诉我正确的方向吗？

这是我的班级:

public class Cache<T>
{
    public string Name { get; set; }

    private  Dictionary<int, T> _dicCache = new Dictionary<int, T>();

    public  void Insert(int objID, T obj)
    {
        try
        {
            _dicCache.Add(objID, obj);

            HttpContext.Current.Cache.Insert(Name, _dicCache, null, DateTime.Now.AddMinutes(10), TimeSpan.FromMinutes(0));
        }
        catch (Exception)
        {
            throw;
        }
    }

    public bool Get(int objID, out T obj)
    {
        _dicCache = (Dictionary<int, T>)HttpContext.Current.Cache.Get(Name);


        try
        {
            return _dicCache.TryGetValue(objID, out obj);
        }
        catch (Exception)
        {
            throw;
        }
    }
 }

以下是我称之为:

   Services.Cache<Entities.User> cache = new Services.Cache<Entities.User>();
   cache.Name = Enum.Cache.Names.usercache.ToString();


   Entities.User user = new Entities.User();

   cache.Get(pUserId, out user);

我也试图改为Get class to:

    public T Get(int objID, out T obj)
    {
        _dicCache = (Dictionary<int, T>)HttpContext.Current.Cache.Get(Name);

        T newObject = (T)Activator.CreateInstance<T>();


        try
        {
            _dicCache.TryGetValue(objID, out newObject);

            obj = newObject;

            return obj;
        }
        catch (Exception)
        {
            throw;
        }
    }

但是我仍然在线上得到相同的NullReferenceException _dicCache.TryGetValue(objID, out newObject);.

Answer 1

我认为,如果您的字典为空,那么您可以拥有该异常的唯一方法.

_dicCache.TryGetValue(objID, out newObject);

null是键的有效参数(如果TKey是引用类型),但在您的情况下它是int.

你确定_dicCache不是null吗？我会检查作业的价值:

_dicCache = (Dictionary<int, T>)HttpContext.Current.Cache.Get(Name);