Question

A method have some methods and also some methods have other methods.
How should I pass an error message to the top method to show the message on the window or the dialog box?
It may not be an error message but an caution message or something.
It would be really nice if you give me an advice about ASP.NET MVC. In ASP.NET MVC, action methods would be the top.

Answer 1

One possibility is to use the TryXXX pattern:

public bool TryXXX(InputType input, out ResultType result, out string errorMessage);

and in your controller:

public ActionResult Foo()
{

    ResultType result;
    out string errorMessage;
    if (!TryXXX(input, out result, out errorMessage))
    {
        ModelState.AddModelError("", errorMessage);
        return View();
    }

    // here you could use the result
    ...

}

Another possibility is to pass the ModelState to the lower layers which will take care of adding the error messages to it so that in your controller action you just need to check ModelState.IsValid after calling some method.

Yet another possibility is to use exceptions but remember that exceptions should be used only to handle exceptional cases. They should be avoided to handle business validation.

There really are different ways and it all depend on what exactly you are trying to do.