Question

Background:
I am new to MVP and just coding my first winform application using Model View Presenter
Question:
I have been browsing for best practices on how to write user input validation code for windows controls (e.g TextBox etc) and where to put that code in winforms application using Model View Presenter desing pattern but still confused.
Let me explain
Suppose I have some TextBox controls on my form, which accept inputs like Name, Phone, email, zip etc. Normally I would call different methods like validateName(), validatePhone(), validateEmail() and validateZip() then in each of these methods I would definitely have to check that the input provided by the user in not empty like

    if(txtName.Text.Length == 0)
   {
      errorMessage = "Name is required.";
         return false;
   }

   if(txtEmail.Text.Length == 0)
   {
      errorMessage = "e-mail address is required.";
         return false;
   }

That smells like code repetition and I think there must be a better and efficient way to check whether the text is not null (may be by looping through all textbox controls).

So, What I am thinking is to have a CommonMethods class containing common methods like CheckifTextEmply(), CheckifNumber() etc and use this class throughout all my forms since these is common functionality and can be used by other TextBox controls on other forms in the project.
Now can you please tell me if
1. Is this the right approach, if not then how should I approach this issue
2. If right, where should I put the CommonMethods class (code) in Model View Presenter design.

Regards,
ZB

Answer 1

Looks a bit old post. Try creating a method which takes control as an argument and then try to validate it.

bool validate(TextBox txt)
{
    return string.IsNUllOrEmpty(txt.Text);
}

you can also try taking a params[] argument to take multiple controls and validate them.

Regarding the error messages, instead of “Name is required” if you go for “required field” message, it will make the job easier. But if not, try creating dictionary of control and bool, pass false if the validation fails and take action according to it.

I know the answer is not very descriptive, but right now, I am a bit busy so cant take much time to explain this. Let me know if it helps.