JSON object to ASP.NET MVC - asp.net-mvc

Question

I know there are multiple threads around this issue, but I still can't figure mine out. Can someone please help me figure out why my classObject always has null value? I feel like I've tried everything by now.
My class:
public class ClassAB
{
[Required]
[MaxLength(100)]
[DataType(DataType.Text)]
public string A{ get; set; }
[Required]
[MaxLength(100)]
[DataType(DataType.MultilineText)]
public string B{ get; set; }
}
My home controller:
[HttpPost]
public ActionResult MyMethod(ClassAB classObject)
{}
and my Javacript call
let data = {
"A": "A",
"B": "B"
}
await fetch(`https://localhost:44359/Home/MyMethod/`, {
method: "POST",
body: JSON.stringify(data),
contentType:"application/json",
success: (result)=>{
console.log(result)
},
failure: (result) => {
alert(result)
}
});

Answer 1

Found the issue. My contentType should have been in header. Modifying request to
await fetch(`https://localhost:44359/Home/MyMethod/`, {
method: "POST",
body: JSON.stringify(data),
headers: {
'Content-Type': 'application/json'
},
success: (result)=>{
console.log(result)
},
failure: (result) => {
alert(result)
}
});
fixed the issue

Answer 2

Try this
var data = [{A: 'A',B:'B'}];
await fetch(`https://localhost:44359/Home/MyMethod/`, {
method: "POST",
body: JSON.stringify(data),
contentType:"application/json",
success: (result)=>{
console.log(result)
},
failure: (result) => {
alert(result)
}
});
[HttpPost]
public ActionResult MyMethod(List<ClassAB > classObject)
{}

Answer 3

WebAPI won't know to model bind an object like that. See https://learn.microsoft.com/en-us/aspnet/core/mvc/models/model-binding?view=aspnetcore-3.1
Try using the [FromBody] attribute
[HttpPost]
public ActionResult MyMethod([FromBody] ClassAB classObject)
{}
When combining this with a proper javascript post this will work, see image.
Sample js
<script>
var xhr = new XMLHttpRequest();
var url = "https://localhost:5001/api/default/MyMethod";
xhr.open("POST", url, true);
xhr.setRequestHeader("Content-Type", "application/json");
xhr.onreadystatechange = function () {
if (xhr.readyState === 4 && xhr.status === 200) {
var json = JSON.parse(xhr.responseText);
console.log(json.email + ", " + json.password);
}
};
var data = JSON.stringify({ "A": "A", "B": "B" });
xhr.send(data);
</script>