Post (React, C# ASP.NET Core) always returning null

Question

I need send a int to a C# server (POST) and then return Json. On server (C#) always comes zero. In JS browser console all right (not null/zero). It's an http 500 error:

Failed to load resource: the server responded with a status of 500

Code:

const CallNextTextFromChoice = (nextChoiceID) => {
        axios.post('https://localhost:7252/Main/NextTextFromChoice', { nextChoiceID: nextChoiceID }, {
            headers: {
                'Content-Type': 'application/json'
            }
        })
            .then(response => {
                const data = response.data;
            })
            .catch(error => {
                console.log(nextChoiceID);
                console.error('Error:', error);
            });
    }

And C# code:

[HttpPost]
public IActionResult NextTextFromChoice(int nextChoiceID)
{
    var nextText = _dataBaseController.UpdateAllInfoWithChoice(nextChoiceID);

    return Json(nextText);
}

console.log(nextChoiceID) is working correctly and outputting the right integer.

I tried native indicate in C# Json data (with attribute [FromBody]), but result did not change. It always appears as null (or zero if using int). The message just doesn't get through

Answer 1

The binding between the incoming request and method is not working as you expect. Change your method to be more explicit about the incoming parameters. Note that I have defined a record to encapsulate the your request parameters.

[HttpPost]
public IActionResult NextTextFromChoice([FromBody] NextChoiceRequest request)
{
    var nextText = _dataBaseController.UpdateAllInfoWithChoice(request.Id);

    return Json(nextText);
}

public record NextChoiceRequest(int Id);

The [FromBody] isn't entirely necessary here as there is no other binding going on and .NET is smart enough to work out the binding. However, it can be benificial to be explicit regardless.