AddMvc 返回一个 IMvcBuilder 实现，它具有相应的 AddJsonOptions 扩展方法。新型方法 AddControllers ， AddControllersWithViews 和 AddRazorPages 还返回 IMvcBuilder 实现。以与链接 AddMvc 相同的方式链接它们：

AddMvc returns an IMvcBuilder implementation, which has a corresponding AddJsonOptions extension method. The new-style methods AddControllers, AddControllersWithViews, and AddRazorPages also return an IMvcBuilder implementation. Chain with these in the same way you would chain with AddMvc:

services.AddControllers()
    .AddJsonOptions(options =>
    {
        // ...
    });

请注意，此处的个选项 Json.NET，但对于较新的 System.Text.Json API。如果您仍然想使用Json.NET，请参见 tymtam的答案

Note that options here is no longer for Json.NET, but for the newer System.Text.Json APIs. If you still want to use Json.NET, see tymtam's answer