C# error messages for incorrect input value (regex) and empty textboxes

Question

Hey there I have a question about Regex and error checking for empty text boxes. I have a windows form application which has a name textbox phone number textbox and email textbox. They all have regex assigned basically when the user clicks the submit button is there a way i can display a messagebox which gives the user info on which textbox has failed? Ie if they enter letters into the phone number text box a message box would pop up and say something like Please no letters only numbers etc etc. Obviously I could use a general messagebox but that seems quite unusable as it doesn't highlight the errors and it might be difficult to pinpoint such errors in some circumstances. Thanks in advance Ari

Vulpes · Answer

The problem with stuff like phone numbers and e-mail addresses is that they have to be in a specific format and so it's difficult to validate them as the user types the characters in. A MaskedTextBox could deal with a fixed length telephone number. For example a US phone number could be masked with '(999)-000-0000'. However you'd be hard-pressed to come up with a mask for an email address.

Poppa Wallace · Answer

Wouldnt it be easier just to allow only numbers in textbox that require numbers and only char in text box that require letters? On the keypress numbers only :- if ((((int)e.KeyChar 57)) && ((int)e.KeyChar != 8)) { e.Handled = true; } else { e.Handled = false; } Jay

Vulpes · Answer

You can't do this using regular expressions. All they can tell you is whether what was entered in the textbox matches the regular expression. If it doesn't match then they can't tell you why. If you wanted to know that then you'd have to do further tests to try and figure out the reason. Those tests could involve further regular expressions to check whether the input includes a letter a number or whatever.