Question

I’m working on an application where the validation (ranges) checks are controlled in the business logic layer. The code looks similar to this:

public string ValidateRange(int value, int lowRange, int highRange, string fieldDesc, System.Web.UI.WebControls.TextBox txtBox)
{
     string msg = "";

     if (value >= lowRange & value <= highRange)
         msg = "";
     else
     {
         msg = "Please enter a value between " + lowRange + " and " + highRange + " for \"" + fieldDesc + ".\"";
         txtBox.Focus();
     }

     return msg;
}

I’m pretty sure I’m doing this incorrectly so I was hoping someone can explain to me the most efficient way of handling the function and BLL so that it can pass to the Presentation layer nicely. My hope is that I can limit my interaction with the BLL to ValidateRange checks on the form’s TextBox controls with a return for each. If I’m approaching this incorrectly, please let me know. If it does work this way, how can I allow the BLL to access the TextBoxes from the Presentation Layer?

Thanks for your help.

Answer 1

I wouldn’t try to have the BLL mess with textboxes or anything that is presentation related. Afterall, the BLL is supposed to be presentation agnostic. Otherwise, should you need to write, say, a Windows Forms presentation layer (to go with your ASP.NET one), you’d have to re-write or add all new methods on your BLL to support accepting System.Windows.Forms.TextBox as well! It defeats the whole purpose of n-tier if the two presentation layers cannot share the same BLL methods/code.

No, you’ll want to remove any traces of textboxes and such from the BLL and instead write code for auto-focusing invalid textboxes in the presentation layer itself.

If you are using ASP.NET’s built-in validation stuff (Page.IsValid and CausesValidation and the like), you’ll just have to resort to checking which validator came back false and set the focus that way. You can still have your BLL provide the error message.

For example, using a CustomValidator, you could have it call your BLL method ValidateRange. If the return value is String.Empty, return true (valid). If it is non-empty/non-null, you know you got an error, so set the CustomValidator’s ErrorMessage and/or Text properties to the string returned and then return false (invalid).