Added pagination to EconItems#GetSchemaItemsForTF2Async() (#105)

* Updated Next property to be of type uint?

If this is too breaking a change, a consideration for `uint` with a default value of 0 would work, but 0 is still a valid value for "start" on the request.

* Updated IEconItems/EconItems#GetSchemaItemsForTF2Async.

added a `uint? start = null` optional property.

* Modified unit tests to take the new Next/start combination.

This verifies that both a) the Next property is valid on each request, and b) that passing `start` along works as intended. This replaces the original test, but could be put alongside it instead.

Author: QuantumToasted

src/Steam.UnitTests/EconItemsTeamFortress2Tests.cs

@@ -20,9 +20,17 @@ public EconItemsTeamFortress2Tests()
         [Fact]
         public async Task GetSchemaItemsForTF2Async_Should_Succeed()
         {
-            var response = await steamInterface.GetSchemaItemsForTF2Async();
-            Assert.NotNull(response);
-            Assert.NotNull(response.Data);
+            uint? next = null;
+
+            do
+            {
+                var response = await steamInterface.GetSchemaItemsForTF2Async(start: next);
+                Assert.NotNull(response);
+                Assert.NotNull(response.Data);
+
+                next = response.Data.Result.Next;
+            }
+            while (next.HasValue);
         }
 
         [Fact]

src/SteamWebAPI2/Interfaces/EconItems.cs

@@ -81,7 +81,7 @@ public async Task<ISteamWebResponse<EconItemResultModel>> GetPlayerItemsAsync(ul
         /// </summary>
         /// <param name="language"></param>
         /// <returns></returns>
-        public async Task<ISteamWebResponse<SchemaItemsResultContainer>> GetSchemaItemsForTF2Async(string language = "en_us")
+        public async Task<ISteamWebResponse<SchemaItemsResultContainer>> GetSchemaItemsForTF2Async(string language = "en_us", uint? start = null)
         {
             if (appId != (int)AppId.TeamFortress2)
             {
@@ -91,6 +91,7 @@ public async Task<ISteamWebResponse<SchemaItemsResultContainer>> GetSchemaItemsF
             List<SteamWebRequestParameter> parameters = new List<SteamWebRequestParameter>();
 
             parameters.AddIfHasValue(language, "language");
+            parameters.AddIfHasValue(start, "start");
 
             var steamWebResponse = await steamWebInterface.GetAsync<SchemaItemsResultContainer>("GetSchemaItems", 1, parameters);
 

src/SteamWebAPI2/Interfaces/IEconItems.cs

@@ -8,7 +8,7 @@ public interface IEconItems
     {
         Task<ISteamWebResponse<EconItemResultModel>> GetPlayerItemsAsync(ulong steamId);
 
-        Task<ISteamWebResponse<SteamWebAPI2.Models.GameEconomy.SchemaItemsResultContainer>> GetSchemaItemsForTF2Async(string language = "en_us");
+        Task<ISteamWebResponse<SteamWebAPI2.Models.GameEconomy.SchemaItemsResultContainer>> GetSchemaItemsForTF2Async(string language = "en_us", uint? start = null);
 
         Task<ISteamWebResponse<SteamWebAPI2.Models.GameEconomy.SchemaOverviewResultContainer>> GetSchemaOverviewForTF2Async(string language = "en_us");
 

src/SteamWebAPI2/Models/GameEconomy/SchemaItemResultContainer.cs

@@ -15,7 +15,7 @@ public class SchemaItemsResult
         public IList<SchemaItem> Items { get; set; }
 
         [JsonProperty("next")]
-        public uint Next { get; set; }
+        public uint? Next { get; set; }
     }
 
     public class SchemaItemsResultContainer