zoukankan      html  css  js  c++  java
  • Cannot convert type SomeClass to 'T'

    以下代码会出问题:

    public static T Protect<T>(Func<T> func, UserLevel pageRole) where T : ActionResult, new()
    {
        try
        {
            return func();
        }
        catch (Exception err)
        {
            if (typeof(T) is JsonResult)
            {
                return (T)new JsonResult() ;

            }
            else if (typeof(T) is ActionResult)
            {
                return (T)new ContentResult();
            }

            throw err;
        }
    }

    得到 Cannot convert type 'JsonResult'  to 'T',应该修正为:

    return (T)(object)new JsonResult();

    Well, you can always placate the compiler by adding an object cast in the middle:

    geoConfigs = (T)(object)GetGeoConfigurationNumericFromDB(items, maMDBEntities);

    which will defer the type-check until runtime. However! There is no compiler way to do this otherwise, as it is never going to be happy with string tests like "MamConfiguration". Also, generics work well when the code is ... generic - i.e. does the same thing which each type. The code shown is the opposite of generic. It is non-generic code exposed through a generic API. It is always going to be messy inside. Personally I would try to avoid this usage in the first place.

    或者:

    You should be able to just use Convert.ChangeType() instead of your custom code:

    public T Get<T>(Stats type) where T : IConvertible
    {
        return (T) Convert.ChangeType(PlayerStats[type], typeof(T));
    }
  • 相关阅读:
    css 自动调整不同 大小的图片变成一定大小
    myeclipse 修改html 报错
    js 中json的使用
    对比两个文件相似度 余弦算法
    andriod 解包
    http post/get 请求
    VXLAN 静态隧道实现同网段通信
    网络设备巡检命令
    IPv6
    Cisco ASA 调整terminal屏幕
  • 原文地址:https://www.cnblogs.com/luminji/p/4018876.html
Copyright © 2011-2022 走看看