返回JSON格式的数据：

public class ClientController : Controller
{
    public JsonResult CountryLookup()
    {
         var countries = new List<SearchTypeAheadEntity>
         {
             new SearchTypeAheadEntity {ShortCode = "US", Name = "United States"},
             new SearchTypeAheadEntity {ShortCode = "CA", Name = "Canada"}
         };

         return Json(countries);
    }
}

在代码中，将To JsonRequestBehavior.AllowGet替换为new Newtonsoft.Json.JsonSerializerSettings()
它的工作原理与JsonRequestBehavior.AllowGet相同

public class ClientController : Controller
{
  public ActionResult CountryLookup()
  {
    var countries = new List<SearchTypeAheadEntity>
        {
            new SearchTypeAheadEntity {ShortCode = "US", Name = "United States"},
            new SearchTypeAheadEntity {ShortCode = "CA", Name = "Canada"}
        };

    return Json(countries, new Newtonsoft.Json.JsonSerializerSettings());
  }
}

有时候你需要用JSON返回一条消息，只需使用如下JSON结果，不再需要jsonrequestbehavior，下面是简单的代码：

public ActionResult DeleteSelected([FromBody]List<string> ids)
{
    try
    {
        if (ids != null && ids.Count > 0)
        {
            foreach (var id in ids)
            {
                bool done = new tblCodesVM().Delete(Convert.ToInt32(id));
                
            }
            return Json(new { success = true, responseText = "Deleted Scussefully" });

        }
        return Json(new { success = false, responseText = "Nothing Selected" });
    }
    catch (Exception dex)
    {
        
        return Json(new { success = false, responseText = dex.Message });
    }
}

你好作为控制器中接受的答案，你不必说

return Json(countries, JsonRequestBehavior.AllowGet);

只管写

return Json(countries);

但是在 AJAX 的cshtml中，你应该用小写字母来调用你的实体属性，比如：shortCode和name。

$.ajax({
                method: "GET",
                url: `/ClientController/CountryLookup`
            }).done(function (result) {
                for (var i = 0; i < result.length; i++) {
                        var shortCode=result[i].shortCode;
                        var name= result[i].name;
                }

            })

我一直在移植一个网站从asp.net到ASP.NET核心。我取代：return Json(data, JsonRequestBehavior.AllowGet);与Json(data, new System.Text.Json.JsonSerializerOptions());和一切又开始工作。