How to return view along with model in Async task in Asp.Net MVC - asp.net-mvc

Question

I am testing asynch task in MVC and creating asynchronous task following code. When I return model value along with view name return View("Index", EmpResponse), I am getting error. but if I simply return view return view(). it is working well.
public class AsynchController : Controller
{
string Baseurl = "http://dummy.restapiexample.com/api/v1/";
// GET: Asynch
public async Task<ActionResult> Index()
{
using (var client = new HttpClient())
{
//Passing service base url
client.BaseAddress = new Uri(Baseurl);
client.DefaultRequestHeaders.Clear();
//Define request data format
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
//Sending request to find web api REST service resource GetAllEmployees using HttpClient
HttpResponseMessage Res = await client.GetAsync("employees");
var EmpResponse = "";
//Checking the response is successful or not which is sent using HttpClient
if (Res.IsSuccessStatusCode)
{
//Storing the response details recieved from web api
EmpResponse = Res.Content.ReadAsStringAsync().Result;
//Deserializing the response recieved from web api and storing into the Employee list
}
//returning the employee list to view
return View("Index", EmpResponse);
}
}
In simply ActionResult, I know we can return view name and model both together. is it issue with Async task?

Answer 1

Your intention is to pass EmpResponse as the view-model for your Index view, but since you have already deserialized EmpResponse as a string, it matches the wrong overload of the View() helper method (the one which accepts both viewName and masterName).
Try to pass it as an object to match the correct overload:
return View("Index", EmpResponse as object);
A better approach would be to store the received data as a strongly-typed collection of objects:
var empResponse = await Res.Content.ReadAsAsync<IEnumerable<Employee>>();
Then pass it as a view-model:
return View("Index", empResponse);

Answer 2

This isn't really an async issue, but a model type issue. (Though there is an async issue waiting to become a problem... Don't call .Result directly, but instead use await to get the result.)
Your model is a string. But the overload for View() which takes a second string uses it to find a named view. Which is why it's looking for a view called your long JSON string. (Well, a "master view" in this case since you're sending it two strings.)
Don't use a string as a model. Use a model. Instead of sending one big JSON string to your view, deserialize it into a model of some sort. The type is up to you, but the deserialization might look something like:
var response = await client.GetAsync("employees");
YourModelTypeHere model = null;
if (response.IsSuccessStatusCode)
{
var responseString = await result.Content.ReadAsStringAsync();
model = JsonConvert.DeserializeObject<YourModelTypeHere>(responseString);
}
return View(model);
There may even be an option in result to read/deserialize as your model directly, saving you a line of code above. But the overall principle is the same. Use strongly typed models instead of complex serialized strings.
*In this case, YourModelTypeHere looks like it would in fact be an IEnumerable<YourModel> or perhaps an IList<YourModel>, based on the serialized JSON we're seeing.
*Note also that this uses your current logic of sending an empty model to the same view if nothing was successfully retrieved. For an empty string that may be okay, for null it may become problematic depending on what your view is doing. (Either way your view is going to have to change if it currently expects a string as a model.) Perhaps redirect or return an error in the case of no available model? The logic of how your system should behave is up to you.