Dynamically enable or disable RequiredFieldValidator based on value of DropDownList

Question

I have an ASP.NET form with three text inputs, one each for "Work Phone", "Home Phone" and "Cell Phone". Each of these text inputs has a RequiredFieldValidator associated with it. I also have a DropDownList where the user can select the preferred phone type.

I want to only require the field that is selected in the DropDownList. For example, if the user selects "Work Phone" from the DropDownList, I want to disable the RequiredFieldValidator for "Home Phone" and "Cell Phone", thereby only making the "Work Phone" field required.

I have a method that enables and disables these validators based on the value of the DropDownList, but I cannot figure out when to call it. I want this method to run before the validation takes place on the page. How would I do that?

Answer 1

OnChange of the DropDownlist, you will need to register a server-side event handler that enables/disables the validator...

HTH

Answer 2

You can do this with JavaScript like this:

ValidatorEnable(RequiredFieldValidatorId, false);

Then have your drop down list use the onchange event (I'd suggest using jQuery)

$("#<%=dropDownList.ClientID %>").change(function(){
    var val = $(this).val();
    var skip = null;
    if (val == 1)
       skip = "workPhoneValidator";
    else if (val == 2)
       skip = "cellPhoneValidator";
    ....

    if (skip != "workPhoneValidator") ValidatorEnable(workPhoneValidator, false);
    if (skip != "cellPhoneValidator") ValidatorEnable(cellPhoneValidator, false);
    ....
});

Answer 3

OnChange event of the drop down you may have something like this

function EnableValidator(){
  if(validatorMustBeEnabled)
    ValidatorEnable(requiredFieldValidator, true);
  else
    ValidatorEnable(requiredFieldValidator, false);
} 

Check on this url. Section "Client-Side APIs"

http://msdn.microsoft.com/en-us/library/Aa479045#aspplusvalid_clientside

Answer 4

Possible way would be:

• Set in your DropDownList AutoPostBack="true"
• In the SelectedIndexChanged event handler of the DropDownList enable/disable your validators
• Set in your DropDownList CausesValidation="false" to avoid that the validators block a postback when you change the DropDownList entry.

Answer 5

Why not use a CustomValidator in this case? Turning off/on a RequiredFieldValidator could lead to a design issue in the future - I'd stick to using them on fields that are going to be required.