Get Crypto Price History from GraphQL Backend

Let's write the logic to retrieve the Price History from our GraphQL Backend

1. GetAssetPriceHistory.graphql

Let's first see how StrawberryShake automatically generates C# code based on our *.graphql files

1. In Visual Studio, open Services/GraphQL/Operations/GetAssetPriceHistory.graphql

2. Here's a breakdown of how Strawberry Shake turns this GraphQL query into C# code:

   GetAssetPriceHistory.graphql	Strawberry Shake
   query GetAssetPriceHistoryQuery($symbol:String!, $after: String, $span: ChangeSpan!)	Generates a Method, GetAssetPriceHistoryQuery.ExecuteAsync(string symbol, string? after, ChangeSpan span, CancellationToken token)
   price	Generates an interface, interface IGetAssetPriceHistoryQuery_AssetBySymbol_Price
   change	Generates an interface, interface IGetAssetPriceHistoryQuery_AssetBySymbol_Price_Change
   history	Generates an interface, interface IGetAssetPriceHistoryQuery_AssetBySymbol_Price_Change_History
   pageInfo	Generates an interface, interface IGetAssetPriceHistoryQuery_AssetBySymbol_Price_Change_History_PageInfo

2. Add GetPriceHistory Logic

1. In Visual Studio, open Services/GraphQL/CryptoGraphQLService.cs

2. In CryptoGraphQLService, update the GetPriceHistory method with the following code:

   public async IAsyncEnumerable<IGetAssetPriceHistoryQuery_AssetBySymbol_Price_Change_History_Nodes?> GetPriceHistory(string symbol, [EnumeratorCancellation] CancellationToken token, ChangeSpan span = ChangeSpan.Day)
   {
       string? endCursor = null;
       IGetAssetPriceHistoryQueryResult? queryResult;
   
       do
       {
           var result = await _cryptoClient.GetAssetPriceHistoryQuery.ExecuteAsync(symbol, endCursor, span, token).ConfigureAwait(false); // Executes the GetAssetPriceHistoryQuery
           result.EnsureNoErrors(); // Throws a GraphQLClientException if the GraphQL Server returns an error
   
           queryResult = result.Data;
   
           var priceHistoryNodes = queryResult?.AssetBySymbol?.Price?.Change?.History?.Nodes ?? Array.Empty<IGetAssetPriceHistoryQuery_AssetBySymbol_Price_Change_History_Nodes>();
   
           foreach (var node in priceHistoryNodes)
           {
               if (node is not null)
                   yield return node;
           }
   
           endCursor = queryResult?.AssetBySymbol?.Price?.Change?.History?.PageInfo?.EndCursor; // Upates the endCursor (used for pagination)
       }
       while (queryResult?.AssetBySymbol?.Price?.Change?.History?.PageInfo?.HasNextPage is true); // Continues pagination until HasNextPage is false
   }

5. View Price History

1. In Visual Studio, build + deploy the Android app to the Android Emulator
2. In the Android Emulator, on the Dashboard page, verify the price history is now populated on the charts

3. In the Android Emulator, navigate to the Screener page
4. On the Screener page, tap on the first item in the list
5. On the Asset page, confirm the Asset Chart data is populated

6. On the Asset page, view the entire asset price history by tapping the All button