Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Teams

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

I have an asp.net core 2.1 project and I'm getting the following error in my controller action:

Cannot implicitly convert type 'Microsoft.AspNetCore.Mvc.BadRequestObjectResult' to 'System.Collections.Generic.IList'. An explicit conversion exists (are you missing a cast?)

This is my code:

[HttpPost("create")]
[ProducesResponseType(201, Type = typeof(Todo))]
[ProducesResponseType(400)]
public async Task<IList<Todo>> Create([FromBody]TodoCreateViewModel model)
    if (!ModelState.IsValid)
        return BadRequest(ModelState);   // This is the line that causes the intellisense error
    await _todoRepository.AddTodo(model);
    return await GetActiveTodosForUser();
[HttpGet("GetActiveTodosForUser")]
[ProducesResponseType(200)]
[ProducesResponseType(404)]
public async Task<IList<Todo>> GetActiveTodosForUser(string UserId = "")
    if (string.IsNullOrEmpty(UserId))
        UserId = HttpContext.User.FindFirstValue(ClaimTypes.Sid);
    return await _todoRepository.GetAll(UserId, false);
What am I doing wrong?
                Your function is written to return Task<IList<Todo>> and  BadRequest(ModelState) obviously inst't of that type
– Matěj Štágl
                Aug 13, 2018 at 7:15
Your action return type does not take in mind possible BadRequest.
Instead of direct usage of IList<Todo> you need to wrap it with generic ActionResult type.
public async Task<ActionResult<IList<Todo>>> Create(...
Here are the related docs.
For ASP.NET Core 2.1, you should use ActionResult<T> but there is a limitation with Interface's.
This Works
public ActionResult<IList<string>> Create()
    return new List<string> { "value1", "value2" };
Doesn't Work
public ActionResult<IList<string>> Create()
    //DOESN'T COMPILE:
    //Error CS0029  Cannot implicitly convert type
    //'System.Collections.Generic.IList<string>' 
    //to 'Microsoft.AspNetCore.Mvc.ActionResult<System.Collections.Generic.IList<string>>'
    //the cast here is for demo purposes.
    //the problem will usually arise from a dependency that returns
    //an interface.
    var result = new List<string> { "value1", "value2" }
                     as IList<string>;
    return result;
  
C# doesn't support implicit cast operators on interfaces.
  Consequently, conversion of the interface to a concrete type is
  necessary to use ActionResult.
Source: ActionResult type
below ASP.NET Core 2.1, 

public async Task<IActionResult> Create([FromBody]TodoCreateViewModel model)
Then it will work.
And for ASP.NET Core 2.1 as suggested by @amankkg,
public async Task<ActionResult<IList<Todo>>> Create([FromBody]TodoCreateViewModel model)
                I want to create the ToDo then return the list of all the ToDos for the user which is why I'm returning a List
– Robbie Mills
                Aug 13, 2018 at 7:21
                @spottedmahn I'm using Interfaces with ActionResult, then how you can say that it doesn't work. ActionResult<IEnumerable<PartViewModel>> Get(), Working example is here: devniggaspk.azurewebsites.net/admin/api/course/1/Clips/…
– Muhammad Waqas Dilawar
                Oct 29, 2018 at 6:41
        
Thanks for contributing an answer to Stack Overflow!
Please be sure to answer the question. Provide details and share your research!
But avoid …
Asking for help, clarification, or responding to other answers.
Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.