Multiple WCF service contrct

If you have shared data between logically distinct sets of operations it is generally much easier to implement multiple contracts on a single service rather than implementing a custom ServiceHost which supports dependency injection. Especially if you are new to WCF. A common pattern is the use of partial classes like this:

[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Single, InstanceContextMode = InstanceContextMode.PerCall)]
partial class DownloadService : IDownload
{
  //Various download function like Add, Remove, Start, Stop, etc. go here
}

partial class DownloadService : ISettings
{
  //Settings functions related to download functionality go here
}

[ServiceContract(SessionMode = SessionMode.Allowed)]
interface IDownload
{
  [OperationContract(IsOneWay = true)]
  void AddDownload(Download download);
  //Then whatever other functions to download you use
}

[ServiceContract(SessionMode = SessionMode.Allowed)]
interface ISettings
{
  [OperationContract(IsOneWay = true)]
  void SaveSettings();
  //Other functions for settings like Add, Remove, Load, etc.
}

[DataContract]
struct Download
{
  [DataMember]
  public string Name {get; private set;}
  [DataMember]
  public int Packet {get; private set;}
  public Download(string name, int packet)
  {
    Name = name;
    Packet = packet;
  }
}

So in this example this service is used to download from somewhere. You also want various settings that let you control how the DownloadService functions. Well, this is obviously going to require some shared data between the settings and DownloadService. A quick and easy way to go about that is simply to wrap up both functionalities into a single service and expose multiple contracts - one for downloading and one for settings. A more advanced solution that's more in line with SOLID[^] principles would be to derive your own ServiceHost class which injects the shared dependency into service instances. I have a tip/trick here[^] that can show you how to accomplish this but I'd stick to simple solutions while learning :)

Hope this helped!