.net core 3.1 mvc string接收为null解决方案

多参数传值，string为null解决

1、添加类

public class CustomMetadataProvider : IMetadataDetailsProvider, IDisplayMetadataProvider
    {
        public void CreateDisplayMetadata(DisplayMetadataProviderContext context)
        {

            if (context.Key.MetadataKind == ModelMetadataKind.Property
                || context.Key.MetadataKind == ModelMetadataKind.Parameter
                || context.Key.MetadataKind == ModelMetadataKind.Type)
            {

                context.DisplayMetadata.ConvertEmptyStringToNull = false;
            }
        }
    }

2、注册类

services.AddControllersWithViews(options => options.ModelMetadataDetailsProviders.Add(new CustomMetadataProvider()))

　　

对象传值，string为null

1、修改3.1默认的json

//services.AddMvc().AddJsonOptions(options =>
            //{
            //    options.JsonSerializerOptions.PropertyNamingPolicy = null;
            //});


            services.AddMvc(options =>
            {
                options.EnableEndpointRouting = false;
            }).SetCompatibilityVersion(CompatibilityVersion.Version_3_0)
            .AddNewtonsoftJson(options =>
            {
　　　　　　　　　　// 自定义的返回处理
                options.SerializerSettings.DateFormatHandling = Newtonsoft.Json.DateFormatHandling.MicrosoftDateFormat;
                options.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss";
                options.SerializerSettings.NullValueHandling = Newtonsoft.Json.NullValueHandling.Include;
                options.SerializerSettings.DefaultValueHandling = Newtonsoft.Json.DefaultValueHandling.Include;
                options.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver();
                options.SerializerSettings.ConstructorHandling = Newtonsoft.Json.ConstructorHandling.Default;
                options.SerializerSettings.StringEscapeHandling = Newtonsoft.Json.StringEscapeHandling.Default;
                options.SerializerSettings.FloatParseHandling = Newtonsoft.Json.FloatParseHandling.Double;
                options.SerializerSettings.ObjectCreationHandling = Newtonsoft.Json.ObjectCreationHandling.Replace;
                options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
                options.SerializerSettings.Converters.Add(new EmptyStringToNullJsonConverter());
            });

　　

2、使用JObject接收数据

public string UpdateCompany([FromBody] JObject value)
        {
            string jsonStr = JsonConvert.SerializeObject(value);
            CompanyInfo rcompany = JsonConvert.DeserializeObject<CompanyInfo>(jsonStr);
        }

　　

3、关于接收的对象为null问题

关键在于

data: JSON.stringify(paras),
contentType: 'application/json'