无法检查数组是否为空

Question

i have the folloiwng action method inside my asp.net mvc application:-

 public ActionResult CustomersDetails(long[] SelectRight)
        {

            if (SelectRight == null)
            {
                ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists see your system administrator.");
                RedirectToAction("Index");
            }
            else
            {
                var selectedCustomers = new SelectedCustomers
                {
                    Info = SelectRight.Select(GetAccount)
                };




                return View(selectedCustomers);
            }
            return View();
        }

But if the SelectRight Array is empty then it will bypass the if (SelectRight == null) check and it will render the CustomerDetails view and raise an exception on the following code inside the view

@foreach (var item in Model.Info) {
    <tr>

So how can i make the null check works fine?

Answer 1

You have to return the result of RedirectToAction(..) .

 public ActionResult CustomersDetails(long[] SelectRight)
 {
      if (SelectRight == null)
      {
           ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists see your system administrator.");
           return RedirectToAction("Index");
      }
      else
      {
           '...

Answer 2

You can change the condition to the following one:

...
if (SelectRight == null || SelectRight.Length == 0)
...

That should help.

EDIT

The important thing to note about the code above is that in c#, the or operator || is short circuiting. It sees that the array is null (statement is true) and does NOT attempt to evaluate the second statement ( SelectRight.Length == 0 ) so no NPE is thrown.

Answer 3

You could check that it isn't null, and doesn't have a length of zero.

if (SelectRight == null || SelectRight.Length == 0) {
    ModelState.AddModelError("", "Unable to save changes...");
    return RedirectToAction("Index");
}

Above if-statement would catch both null-values and empty arrays.