Interface cannot declare types

Question

My problems : I'm trying to follow this tutorial about a wcf service linked with a windows form and using a database: http://www.c-sharpcorner.com/uploadfile/rohatash/insert-and-display-data-in-datagridview-in-windows-forms-app/

When I run the code I get 2 errors about : 'IService1' : interfaces cannot declare types.
'UserDetails' : interfaces cannot declare types.

I've looked for answers on stackoverflow and google but the only questions that was close to mine was unanswered. Also some comments tell it works for them so is it a code problem or maybe a configuration one. I put the code of my 2 files IService.cs and Service.cs here : the IService.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Web;
using System.Text;
using System.Data.SqlClient;
using System.Data;

namespace WCFServiceForInsert
{
    // REMARQUE : vous pouvez utiliser la commande Renommer du menu Refactoriser pour changer le nom d'interface "IService" à la fois dans le code et le fichier de configuration.
    [ServiceContract]
    public interface IService
    {
        // NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IService1" in both code and config file together.
        [ServiceContract]
        public interface IService1
        {
            [OperationContract]
            string InsertUserDetails(UserDetails userInfo);

            [OperationContract]
            DataSet SelectUserDetails();
        }

        // Use a data contract as illustrated in the sample below to add composite types to service operations.
        [DataContract]
         public class UserDetails
        {
            int id;
            string title;
            string salary;
            string benefits;
            string keywords;
            string jobType;
            string location;
            string startDate;
            string description;
            string recruitmentAgency;
            string agencyContact;
            string agencyPhone;
            string agencyEmail;
            string jobRef;
            string datePosted;
            string dateExpire;

            [DataMember]
            public int JobID
            {
                get { return id; }
                set { id = value; }
            }

            [DataMember]
            public string Title
            {
                get { return title; }
                set { title = value; }
            }
            [DataMember]
            public string Salary
            {
                get { return salary; }
                set { salary = value; }
            }
            [DataMember]
            public string Benefits
            {
                get { return benefits; }
                set { benefits = value; }
            }
            [DataMember]
            public string Keywords
            {
                get { return keywords; }
                set { keywords = value; }
            }
            [DataMember]
            public string JobType
            {
                get { return jobType; }
                set { jobType = value; }
            }
            [DataMember]
            public string Location
            {
                get { return location; }
                set { location = value; }
            }
            [DataMember]
            public string StartDate
            {
                get { return startDate; }
                set { startDate = value; }
            }
            [DataMember]
            public string Description
            {
                get { return description; }
                set { description = value; }
            }
            [DataMember]
            public string RecruitmentAgency
            {
                get { return recruitmentAgency; }
                set { recruitmentAgency = value; }
            }
            [DataMember]
            public string AgencyContact
            {
                get { return agencyContact; }
                set { agencyContact = value; }
            }
            [DataMember]
            public string AgencyPhone
            {
                get { return agencyPhone; }
                set { agencyPhone = value; }
            }
            [DataMember]
            public string AgencyEmail
            {
                get { return agencyEmail; }
                set { agencyEmail = value; }
            }
            [DataMember]
            public string JobRef
            {
                get { return jobRef; }
                set { jobRef = value; }
            }
            [DataMember]
            public string DatePosted
            {
                get { return datePosted; }
                set { datePosted = value; }
            }
            [DataMember]
            public string DateExpire
            {
                get { return dateExpire; }
                set { dateExpire = value; }
            }
        }
    }

}

the Service.cs file :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Web;
using System.Text;
using System.Data.SqlClient;
using System.Data;

namespace WCFServiceForInsert
{
    // REMARQUE : vous pouvez utiliser la commande Renommer du menu Refactoriser pour changer le nom de classe "Service" à la fois dans le code, le fichier svc et le fichier de configuration.
    public class Service : IService
    {
        public DataSet SelectUserDetails()
        {
            SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=registration;User ID=sa;Password=wintellect");
            con.Open();
            SqlCommand cmd = new SqlCommand("Select * from Table", con);
            SqlDataAdapter sda = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            sda.Fill(ds);
            cmd.ExecuteNonQuery();
            con.Close();
            return ds;
        }

        public string InsertUserDetails(IService.UserDetails userInfo)
        {
            string Message;
            Message = "";
            SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=registration;User ID=sa;Password=wintellect");
            con.Open();
            SqlCommand cmd = new SqlCommand("insert into RegistrationTable(Title,Salary,Benefits,Keywords,JobType,Location,StartDate,Description,RecruitmentAgency,AgencyContact,AgencyPhone,AgencyEmail,JobRef,DatePosted,DateExpire) values(@Title,@Salary,@Benefits,@Keywords,@JobType,@Location,@StartDate,@Description,@RecruitmentAgency,@AgencyContact,@AgencyPhone,@AgencyEmail,@JobRef,@DatePosted,@DateExpire)", con);
            cmd.Parameters.AddWithValue("@Title", userInfo.Title);
            cmd.Parameters.AddWithValue("@Salary", userInfo.Salary);
            cmd.Parameters.AddWithValue("@Benefits", userInfo.Benefits);
            cmd.Parameters.AddWithValue("@Keywords", userInfo.Keywords);
            cmd.Parameters.AddWithValue("@JobType", userInfo.JobType);
            cmd.Parameters.AddWithValue("@Location", userInfo.Location);
            cmd.Parameters.AddWithValue("@StartDate", userInfo.StartDate);
            cmd.Parameters.AddWithValue("@Description", userInfo.Description);
            cmd.Parameters.AddWithValue("@RecruitmentAgency", userInfo.RecruitmentAgency);
            cmd.Parameters.AddWithValue("@AgencyContact", userInfo.AgencyContact);
            cmd.Parameters.AddWithValue("@AgencyPhone", userInfo.AgencyPhone);
            cmd.Parameters.AddWithValue("@AgencyEmail", userInfo.AgencyEmail);
            cmd.Parameters.AddWithValue("@JobRef", userInfo.JobRef);
            cmd.Parameters.AddWithValue("@DatePosted", userInfo.DatePosted);
            cmd.Parameters.AddWithValue("@DateExpire", userInfo.DateExpire);
            int result = cmd.ExecuteNonQuery();
            if (result == 1)
            {
                Message = userInfo.Title + " Details inserted successfully";
            }
            else
            {
                Message = userInfo.Title + " Details not inserted successfully";
            }
            con.Close();
            return Message;
        }
    }
}

Answer 1

Just move your class outside of the Interface definition. Also, it is best practice not to nest interfaces (for C#, it is generally best practice to use 1 class/interface per file)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Web;
using System.Text;
using System.Data.SqlClient;
using System.Data;

namespace WCFServiceForInsert
{

// REMARQUE : vous pouvez utiliser la commande Renommer du menu Refactoriser pour changer le nom d'interface "IService" à la fois dans le code et le fichier de configuration.
// There is not a reason to keep this IService unless it is necessary for some other piece of your code
[ServiceContract]
public interface IService
{


}

    // NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IService1" in both code and config file together.
    [ServiceContract]
    public interface IService1
    {
        [OperationContract]
        string InsertUserDetails(UserDetails userInfo);

        [OperationContract]
        DataSet SelectUserDetails();
    }


    // Use a data contract as illustrated in the sample below to add composite types to service operations.
    // You must declare this outside of the Interface definition.
    [DataContract]
     public class UserDetails
    {
        int id;
        string title;
        string salary;
        string benefits;
        string keywords;
        string jobType;
        string location;
        string startDate;
        string description;
        string recruitmentAgency;
        string agencyContact;
        string agencyPhone;
        string agencyEmail;
        string jobRef;
        string datePosted;
        string dateExpire;

        [DataMember]
        public int JobID
        {
            get { return id; }
            set { id = value; }
        }

        [DataMember]
        public string Title
        {
            get { return title; }
            set { title = value; }
        }
        [DataMember]
        public string Salary
        {
            get { return salary; }
            set { salary = value; }
        }
        [DataMember]
        public string Benefits
        {
            get { return benefits; }
            set { benefits = value; }
        }
        [DataMember]
        public string Keywords
        {
            get { return keywords; }
            set { keywords = value; }
        }
        [DataMember]
        public string JobType
        {
            get { return jobType; }
            set { jobType = value; }
        }
        [DataMember]
        public string Location
        {
            get { return location; }
            set { location = value; }
        }
        [DataMember]
        public string StartDate
        {
            get { return startDate; }
            set { startDate = value; }
        }
        [DataMember]
        public string Description
        {
            get { return description; }
            set { description = value; }
        }
        [DataMember]
        public string RecruitmentAgency
        {
            get { return recruitmentAgency; }
            set { recruitmentAgency = value; }
        }
        [DataMember]
        public string AgencyContact
        {
            get { return agencyContact; }
            set { agencyContact = value; }
        }
        [DataMember]
        public string AgencyPhone
        {
            get { return agencyPhone; }
            set { agencyPhone = value; }
        }
        [DataMember]
        public string AgencyEmail
        {
            get { return agencyEmail; }
            set { agencyEmail = value; }
        }
        [DataMember]
        public string JobRef
        {
            get { return jobRef; }
            set { jobRef = value; }
        }
        [DataMember]
        public string DatePosted
        {
            get { return datePosted; }
            set { datePosted = value; }
        }
        [DataMember]
        public string DateExpire
        {
            get { return dateExpire; }
            set { dateExpire = value; }
        }
    }


 }