ASP.NET AJAX Server-Side Validation - ServerSideValidationExtender in Validation Guidance Bundle
by David Hayden ( Florida .NET Developer ), Filed: ASP.NET 2.0, Web Client Software Factory
My brain is working overtime on the simple concept of doing server-side validation using ASP.NET AJAX in webforms just like the ServerSideValidationExtender in the Validation Guidance Bundle. I really dig the ServerSideValidationExtender Control, but am trying to better understand alternative solutions and the pros and cons of each.
The code I am working from today is essentially a strip down version of the QuickStart Tutorial that ships with the Validation Guidance Bundle. Basically I have a page where a user types in a URL and I want to validate that the URL exists by doing a simple WebRequest to the URL from the server. In its simplest form it includes a page with a CustomValidator, ServerSideValidationExtender, and of course the CustomValidator Server Code that checks for the existence of the URL:
Here is a snippet of the page where you can see the ServerSideValidationExtender targeting the CustomValidator Control:
<asp:TextBox
ID="txtUrl"
runat="server">
</asp:TextBox>
<asp:CustomValidator
ID="UrlExistsValidator"
ControlToValidate="txtUrl"
ErrorMessage="Invalid Url."
OnServerValidate="CustomValidator1_ServerValidate"
runat="server">
</asp:CustomValidator><br />
<cc1:ServerSideValidationExtender
ID="ServerSideValidationExtender1"
TargetControlID="UrlExistsValidator"
runat="server">
</cc1:ServerSideValidationExtender>
For more information on the ServerSideValidationExtender, you can see the following:
The user experience is pretty slick, because the ServerSideValidationExtender does a partial-page postback after typing in the URL, letting you know if the URL is valid or not:
The CustomValidator's Validation Code ( which I think I literally copied and pasted from the quickstart tutorial ) is as follows:
protected void CustomValidator1_ServerValidate
(object source, ServerValidateEventArgs args)
{
string url = args.Value;
Uri uri;
if (Uri.TryCreate(url, UriKind.Absolute, out uri))
{
args.IsValid = UriExists(uri);
}
else
{
args.IsValid = false;
}
}
private bool UriExists(Uri uri)
{
try
{
HttpWebRequest request =
(HttpWebRequest)WebRequest.Create(uri);
request.MaximumAutomaticRedirections = 4;
HttpWebResponse response =
(HttpWebResponse)request.GetResponse();
response.Close();
return response.StatusCode == HttpStatusCode.OK;
}
catch
{
return false;
}
}
This is all very, very slick, and quite frankly perfect for my needs even though I realize there are some gotchas with Partial-Page Postbacks. Still, I wondered how I could get this immediate feedback without a partial-page postback, which got me into Client-Side Network Callbacks. I will save that post for next time.
Source: David Hayden ( Florida .NET Developer )
Filed: ASP.NET 2.0, Web Client Software Factory