Array Parameter Empty for jQuery Ajax Call to MVC

Question

I have a simple MVC api method:

[System.Web.Http.HttpPost] // Important: it is not System.Web.Mvc.HttpPost
public void MyMethod(object[] arr)
{
 ...
}

I am calling it using this javascript:

$.ajax({
 url: url,
 method: "POST",
 data: { arr: ['1','2']},
 dataType: "json",
 traditional: true,
 error: function (e) {
 ...
 },
 success: function (res) {
 ...
 }
});

The call is successful but the value of arr in the C# code is an empty array (string[0]). I found multiple samples of such calls suggesting mainly adding the traditional: true but it still doesn't work. I tried also providing data in different formats, e.g.:

• data: { arr: ['1','2']}
• data: { ['1','2']}
• data: ['1','2']
• JSON.stringify(['1', '2'])

and none of these work. Ideas?

• Dmitry Pavlov: Possible duplicate of Pass array to mvc Action via AJAX

Answer 1

You need to specify the [FromBody] parameter:

[System.Web.Http.HttpPost] // Important: it is not System.Web.Mvc.HttpPost
public void MyMethod([FromBody] object[] arr)
{
 ...
}

And your code should be:

$.ajax({
 url: url,
 method: "POST",
 data: ['1','2'],
 dataType: "json",
 traditional: true,
 error: function (e) {
 ...
 },
 success: function (res) {
 ...
 }
});

If you specify a key/value like {Arr: ['1', '2']} then you should create a structure for your body:

class MyMethodPostJson
{
 public List<string> Arr;
}

And use:

[System.Web.Http.HttpPost] // Important: it is not System.Web.Mvc.HttpPost
public void MyMethod([FromBody] MyMethodPostJson arr)
{
 ...
}