How to fix problem of update users in asp.net web API - angularjs

Question

I develop function for update user, but in backend, I have error:
System.NullReferenceException: 'The object reference is not defined to an instance of an object.' users was null.
I think because users is null, and I don't know how to make a call to fill users data. this error displays in the condition if(id!= users.ID) ,how to fix this problem, here is my code:
[ResponseType(typeof(void))]
// [HttpPut]
[AcceptVerbs("OPTIONS")]
public IHttpActionResult PutUsers(string id, Users users)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
if (id != users.Id)
{
return BadRequest();
}
db.Entry(users).State = EntityState.Modified;
try
{
db.SaveChanges();
}
catch (DbUpdateConcurrencyException)
{
if (!UsersExists(id))
{
return NotFound();
}
else
{
throw;
}
}
return StatusCode(HttpStatusCode.NoContent);
}
and this user.controller:
$scope.userEdit = function () {
console.log('edit');
var idsForEdit = [];
angular.forEach($scope.listeOfUsers, function (item,$uibModalInstance, index) {
console.log($scope.listeOfUsers);
if (item.checked) {
console.log(item.checked);
console.log(item.Id);
//idsForEdit.push(item);
$scope.registration.Email=item.Email;
$scope.registration.Password=item.PasswordHash;
$scope.registration.Users_Role=item.Role;
$scope.registration.Site=item.Site;
$scope.registration.Id=item.Id;
$scope.ok = function () {
console.log("ok");
// $scope.Action = "Update";
User.Update({
id: item.Id
}, $scope.Users=item.Users
, function (response) {
console.log(response);
console.log("ok");
SweetAlert.swal({
title: "Opération effectuée avec succès!",
text: "Click pour quitter!",
type: "success"
});
$state.go($state.current, $stateParams, {
reload: true,
inherit: false,
notify: true
});
$uibModalInstance.close();
},
function (err) {
});
console.log($scope.user);
};
}
});
//$scope.isEditDirty==true;
};

Answer 1

Your code should be -
[ResponseType(typeof(void))]
// [HttpPut]
[AcceptVerbs("OPTIONS")]
public IHttpActionResult PutUsers(string id, Users users)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
if(users != null)
{
if (id != users.Id)
{
return BadRequest();
}
db.Entry(users).State = EntityState.Modified;
try
{
db.SaveChanges();
}
catch (DbUpdateConcurrencyException)
{
if (!UsersExists(id))
{
return NotFound();
}
else
{
throw;
}
}
}
return StatusCode(HttpStatusCode.NoContent);
}
Using C# 6.0 new features - Null Conditional Operator
[ResponseType(typeof(void))]
// [HttpPut]
[AcceptVerbs("OPTIONS")]
public IHttpActionResult PutUsers(string id, Users users)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
if (id != users?.Id)
{
return BadRequest();
}
db.Entry(users).State = EntityState.Modified;
try
{
db.SaveChanges();
}
catch (DbUpdateConcurrencyException)
{
if (!UsersExists(id))
{
return NotFound();
}
else
{
throw;
}
}
return StatusCode(HttpStatusCode.NoContent);
}