how to check a particular asp.net validation control is valid?

In a web form there are different asp.net validation controls. Is it possible to check a particular validation control is valid ? For example on leaving focus of textbox, first I will check requiredFieldValidatorUserName is valid ? If it is valid then I wi开发者_JAVA技巧ll check on server using ajax that this user name is not booked already.

Edit:

Explaination: I want to check validity (that input was valid) of a validation control on client side.

Please guide.

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All validator controls implement IValidator which contains the IsValid property.

myValidatorControl.IsValid 

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The best way would be to use a CustomValidator with client side code, as this will display all the error messages, block form submission and also ensure that the validation is repeated at the server side - remember, just because you have client-side validation available, doesn't mean the user's seen it: Always validate your input at the server as well.

Your CustomValidator would then be coded to call the Ajax methods, and would show the error messages correctly to the client:

<asp:Label ID="UserNameLabel" AssociatedControlID="UserName" runat="server">
  UserName *:</asp:Label>
<asp:TextBox ID="UserName" runat="server" />
<asp:RequiredFieldValidator ID="UserNameRequired" runat="server" 
                            ControlToValidate="UserName" EnableClientScript="true"
                            ErrorMessage="You must supply a username!" />
<asp:CustomValidator ID="UserNameCustom" runat="server"
                     ControlToValidate="UserName" 
                     ClientValidationFunction="CheckExisting"
                     OnServerValidate="UserNameCustomValidate"
                     ErrorMessage="Username already taken" />

And your ClientValidationFunction should look something like:

<script type="text/javascript">
  function CheckExisting(source, arguments) {
    // Pass the arguments.Value to your AJAX call:
    if (ajaxCallUserNameTaken(arguments.Value)) {
      arguments.IsValid = false;
    }
  }
</script>

(Obviously, you'll need to write the ajaxCallUserNameTaken method to call your page method/web service/etc.)

Doing it this way will ensure that the validation methods happen as expected; this will get called whenever the user tabs out of the textbox leaving a value (it won't get called if the textbox is empty), and will ensure that the user can't submit the page until they supply a unique value. You'll also want to create the method referenced in OnServerValidate to ensure that the value's good once it hits the server too - this should call the same code that the AJAX endpoint uses to reduce duplication of code, etc.

I was originally going to suggest that you could use the Page_Validators object on the client-side to do some checking in the onBlur event, but I don't really think this is suitable here as it results in more pain:

1. It assumes that although there might be more than one validator on the page, there's only the RequiredFieldValidator on the control we're checking
2. The RequiredFieldValidator isn't fired during OnBlur if a user moves out of a control without setting a value - only if they set and clear the value, so even if isvalid is true, you need to check for an empty string!

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You could do this by setting the ValidationGroup for the Validator control that you want to treat as separate from the others. Make sure it matches the ValidationGroup of the control it's validating (your username field).

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I have just faced the same issue and I Set CausesValidation="true" to the textbox control and it worked. Just give it a try :)

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I have been messing around with this around for a bit and found a rather easy (not so efficient) solution to handle this using jQuery.

Use this function to check the validity of your control:

function validateControl() {
    return $('#YOUR_VALIDATOR_ID').css("visibility") == "visible"

if you're using Display="Dynamic" on your validator then the function is like so:

function validateControl() {
    return return $('#YOUR_VALIDATOR_ID').css("display") == "inline"

Be sure to check the true ID of your validator if you're using a Masterpage, as it will be different than the one in your IDE. Do so by viewing the page source in your browser.

The best solution will be of course to validate your form in some other way, using JavaScript or a CustomValidator that lets you write your own code.