Making parallel api calls and handling each response asynchronously in c#

Question

I have a scenario where I need to make multiple api calls (same api with different parameters) parallely in c# (Xamarin iOS and Xamarin Android). And I don't want to wait for all tasks to complete, instead whenever a response comes I should process it and update the UI accordingly.

Method that needs to be called multiple times

public  async Task<Response> GetProductsAsync(int categoryId, int pageNo = -1, int pageSize = -1)
        {
            try
            {
                string url = "";
                if (pageNo == -1 || pageSize == -1)
                    url = $"catalog/v1/categories/{categoryId}/products";
                else
                    url = $"catalog/v1/categories/{categoryId}/products?page-number={pageNo}&page-size={pageSize}";
                var response = await client.GetAsync(url);
                string responseString = await response.Content.ReadAsStringAsync();
                GetParsedData(response.IsSuccessStatusCode, responseString);
            }
            catch (Exception e)
            {
                apiResponse.status = "internalError";
                apiResponse.data = e.Message;
            }
            return apiResponse;
        }

Answer 1

From calling function you may write the code as below

    public void CallingFunctionToGetProductsAsync() {
        Task.Run(async () =>
        {
            var response = await GetProductsAsync(1);
            ProcessResponse(response);
        });

        Task.Run(async () =>
        {
            var response = await GetProductsAsync(2);
            ProcessResponse(response);
        });
    }

Answer 2

This is how you can wait for multiple tasks asynchron and update the UI whenever any of them completes.

async Task GetSomeProductsAsync( IEnumerable<int> categoryIds )
{
    List<Task<Response>> tasks = categoryIds
        .Select( catId => GetProductsAsync( catId ) )
        .ToList();

    while ( tasks.Any() )
    {
        var completed = await Task.WhenAny( tasks );
        tasks.Remove( completed );
        var response = completed.Result;
        // update the ui from this response
    }
}

As a side note:

You should add ConfigureAwait(false) to your awaiting code in GetProducsAsync to avoid uneccessary sync with the caller thread (wich would be the UI here)

public  async Task<Response> GetProductsAsync(int categoryId, int pageNo = -1, int pageSize = -1)
{
    try
    {
        string url = "";
        if (pageNo == -1 || pageSize == -1)
            url = $"catalog/v1/categories/{categoryId}/products";
        else
            url = $"catalog/v1/categories/{categoryId}/products?page-number={pageNo}&page-size={pageSize}";
        var response = await client.GetAsync(url).ConfigureAwait(false);
        string responseString = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
        GetParsedData(response.IsSuccessStatusCode, responseString);
    }
    catch (Exception e)
    {
        apiResponse.status = "internalError";
        apiResponse.data = e.Message;
    }
    return apiResponse;
}

You can read more about it in Stephen Cleary's blog article: Don't block on Async Code