Asp.net Core Post parameter is always null

问题

I'm sending POST from fiddler:

POST http://localhost:55924/api/Product HTTP/1.1
User-Agent: Fiddler
Host: localhost:55924
Content-Type: application/json; charset=utf-8
Content-Length: 84

{"Ean":"1122u88991","Name":"Post test","Description":"Post test desc"}

But Post method always gets null.

// POST api/Product
[HttpPost]
public IActionResult PostProduct([FromBody]Product product)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState);
    }

    _repo.Add(product);

    return CreatedAtRoute("GetToode",product);
}

When I use [FormBody] product is always null, when not using it product is valued but with all fields being null. Product class is simple.

public class Product
{
    public int ProductID { get; set; }
    public string EAN { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public int? CategoryID { get; set; }
}

i tried adding NullValueHandling to ConfigureServices as proposed in post but no use.

services.AddMvc()
    .AddJsonOptions(jsonOptions =>
    {
        jsonOptions.SerializerSettings.NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore;
    });

回答1:

I just had to correct the double quotes in your POST request and it worked. Try this:

{"Ean":"1122u88991","Name":"Post test","Description":"Post test desc"}

See screenshot below.

回答2:

Had the same problem. It turned out that I had no public parameterless constructor for class of incoming instance. In this case, Product had only protected constructors and parameter was always null no matter what. Hope it helps somebody.

回答3:

I experience a similar problem but I had no check for the validity of the ModelState as the OP. When this happens, inspecting it in debug mode will likely point you to what's wrong with the model:

In this example I was using an invalid string 'A' as test value for a Guid property, so the model was always null.

来源：https://stackoverflow.com/questions/39748153/asp-net-core-post-parameter-is-always-null

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.net

asp.net-core

asp.net-core-webapi