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这是我的模型

using System;
using Newtonsoft.Json;
using Xamarin.Forms;

namespace AMIMobile
{

    public class LoginItemsModel
    {
        [JsonProperty("userid")]
        public long Userid { get; set; }

        [JsonProperty("username")]
        public string Username { get; set; }

        [JsonProperty("password")]
        public object Password { get; set; }

        [JsonProperty("fullname")]
        public string fullname { get; set; }

        [JsonProperty("roleid")]
        public long Roleid { get; set; }

        [JsonProperty("role")]
        public object Role { get; set; }

        [JsonProperty("status")]
        public long Status { get; set; }

        [JsonProperty("logfail")]
        public object Logfail { get; set; }

        [JsonProperty("expire")]
        public string Expire { get; set; }

        [JsonProperty("lastlog")]
        public string Lastlog { get; set; }

        [JsonProperty("email")]
        public string Email { get; set; }

        [JsonProperty("phone")]
        public string Phone { get; set; }

        [JsonProperty("visiblp")]
        public string Visiblp { get; set; }
        [JsonProperty("peaid")]
        public object Peaid { get; set; }

        [JsonProperty("posifull")]
        public object Posifull { get; set; }

        [JsonProperty("posiabbr")]
        public object Posiabbr { get; set; }

        [JsonProperty("deptfull")]
        public object Deptfull { get; set; }

        [JsonProperty("deptabbr")]
        public object Deptabbr { get; set; }

        [JsonProperty("deptarea")]
        public object Deptarea { get; set; }

        [JsonProperty("accesstoken")]
        public string Accesstoken { get; set; }

        [JsonProperty("clientinfo")]
        public object Clientinfo { get; set; }

        [JsonProperty("devicename")]
        public object Devicename { get; set; }

        [JsonProperty("platform")]
        public object Platform { get; set; }

        [JsonProperty("iS_REMEMBERME")]
        public bool ISRememberme { get; set; }

        [JsonProperty("magerror")]
        public string Magerror { get; set; }

        [JsonProperty("statuscode")]
        public long Statuscode { get; set; }

        [JsonProperty("iS_ERRORSTATUS")]
        public bool ISErrorstatus { get; set; }

        public string FullName
        {

            get { return Username; }
        }
        public string FirstName { get; set; }
    }

   

}

and this is my view model

public class LoginViewModel : INotifyPropertyChanged
        {
            // For data binding of activity indicator

            private ObserverableCollection<LoginItemsModel> _fn;
            private ObserverableCollection<LoginItemsModel> Fullname
            {
            }

            public event PropertyChangedEventHandler PropertyChanged;

            protected virtual void OnPropertyChange([CallerMemberName] string propertyName = null)
            {
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
            }



        }

'这显示了属性或索引器必须至少有一个访问器错误我不知道这是什么请帮助我如何修复它们，我的错误在

private ObserverableCollection<LoginItemsModel> Fullname
            {
            }

，我为xamarin移动的应用程序编写C#我是C#新手
我想知道如何修复这个错误，我谷歌这个错误，但我没有找到如何修复这个，我尝试绑定这个形式谷歌和它显示错误对不起我的英语