Question

I tried the following code:

   if (vm.SubmitAction == "Delete")
    {
    throw new DivideByZeroException(); // LOCATION A
    return View();
    accountTable.Delete(vm.Account);
   }

   if (Session["CurrentUrl"] != null ) // LOCATION B
     {

Clicking on Delete takes me to LOCATION A.
When I then step through using F11 it goes next to LOCATION B and then raises and exception:

System.DivideByZeroException was unhandled by user code
Message=Attempted to divide by zero.

Can someone explain why it does not go to the return View() or simply exit the action?

Answer 1

Exceptions are just that. Exceptions. Something didn’t go as planned. And the method can therefore not continue as planned. Instead, the application travels up the call stack to find a catch block that will take care of the exception. If no catch block is found, the application crashes.

MVC got a build in attribute used to handle errors. It’s called [HandleError]. But it does not let the action continue, but it prevents ASP.NET from showing the yellow screen.

A typical try/catch in post actions looks like this:

[HttpPost]
public virtual ActionResult Create(YourModel model)
{
  if (!ModelState.IsValid)
    return View(model);

  try
  {
    var dbEntity = _repository.Get(model.Id);
    Mapper.Map(model, dbEntity);
    _repository.Save(dbEntity);

    return RedirectToAction("Details", new { id = model.Id });
  }
  catch (Exception ex)
  {
    ModelState.AddModelError("", ex.Message);
    //log error here.
    return View(model);
  }
}

You can read more about errors in MVC in my blog.