C# 为什么选择服务器为空？ 视图模型 达尔 APP.config

_DBNameList=servObj.GetDBNamesserverSelected；

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此serverSelected始终作为null传递，这不允许生成我的代码，因此我无法从服务器列表中选择服务器。

\u DBNameList=servObj.GetDBNames\u serverSelected？？您在哪里设置_serverSelected的值？我有两个组合框，一个用于服务器列表，另一个用于数据库，这些数据库应根据上述选定的服务器填充。ViewModel:_ServerNameList=servObj.getServerName_DBNameList=servObj.GetDBNamesserverSelected；serverCommand=newrelaycommandfetchserver；public void fetchServerobject server{serverSelected=server.ToString；}DAL用于服务器组合框填充：public List GetServerstring server{var keys=ConfigurationManager.AppSettings.keys；return keys.Cast.Wherekey=>key.ToString.ToLower.Containsserver.ToLower.Selectkey=>ConfigurationManager.AppSettings.Getkey.ToString.ToList；}

string _serverSelected;
        public string serverSelected
        {
            get { return _serverSelected; }
            set
            {
                if (_serverSelected != value)
                    _serverSelected = value;

                RaisePropertyChanged("serverSelected");              
            }
        }

        public BackUpViewModel()
        {

             BackUpContext servObj = new BackUpContext();                      
            _DBNameList = servObj.GetDBNames(serverSelected);
        }

public List<string> GetDBNames(string sqlServerName)
        {
    List<string> lstDBName = new List<string>();         


                SqlConnectionStringBuilder connection = new SqlConnectionStringBuilder();
                connection.DataSource = sqlServerName;
                connection.IntegratedSecurity = true;
                String strCon = connection.ToString();
                SqlConnection sqlConn = new SqlConnection(strCon);
                sqlConn.Open();

                SqlCommand cmd = new SqlCommand("select * from sys.databases", sqlConn);
                SqlDataReader dr = cmd.ExecuteReader();
                while (dr.Read())
                {
                    lstDBName.Add(dr[0].ToString());
                }
                sqlConn.Close();


                return lstDBName;
}