wcf 开发时服务引用的几种方法，到底什么时候关闭服务代理最好

Question

第一种方法：在析构函数中关闭    public class AutoSys_Company
    {
        private AutoSys_CompanyService.AutoSys_CompanyClient client;        public AutoSys_Company()
        {
            client = new XFS.WebClient.AutoSys_CompanyService.AutoSys_CompanyClient();
            if (client.State != System.ServiceModel.CommunicationState.Opened)
            {
                client.Open();
            }
        }        ~AutoSys_Company()
        {
            if (client.State == System.ServiceModel.CommunicationState.Opened)
            {
                client.Close();
            }
        }        public bool Exists(string FName, int FCompanyID)
        {
            return client.Exists(FName, FCompanyID);
        }
}
第二种方法：随时关闭    public class AutoSys_Company
    {
        public bool Exists(string FName, int FCompanyID)
        {
            AutoSys_CompanyService.AutoSys_CompanyClient client=new XFS.WebClient.AutoSys_CompanyService.AutoSys_CompanyClient();
            client.Open();
            bool ret = client.Exists(FName, FCompanyID);
            client.close();
            return ret;
        }
}
第三种方法：不关闭    public class AutoSys_Company
    {
        public bool Exists(string FName, int FCompanyID)
        {
            AutoSys_CompanyService.AutoSys_CompanyClient client=new XFS.WebClient.AutoSys_CompanyService.AutoSys_CompanyClient();
            client.Open();
            bool ret = client.Exists(FName, FCompanyID);
            return ret;
        }
}