How can I code a Created-201 response using IHttpActionResult

In ASP.NET Core, an IActionResult can be returned. This means you can return a ObjectResult with a 201 status code.

[HttpPost]
public async Task<IActionResult> PostAsync([FromBody] CreateModel createModel)
{
    // Create domain entity and persist
    var entity = await _service.Create(createModel);

    // Return 201
    return new ObjectResult(entity) { StatusCode = StatusCodes.Status201Created };
}

If your view derives from ApiController, you should be able to call the Created method from base class to create such a response.

Sample:

[Route("")]
public async Task<IHttpActionResult> PostView(Guid taskId, [FromBody]View view)
{
    // ... Code here to save the view

    return Created(new Uri(Url.Link(ViewRouteName, new { taskId = taskId, id = view.Id })), view);
}