The ControlAdapter is available since .NET framework version 2.0 and his main goal is to adapt and customize a control render in order to achieve a specific behavior or layout. This customization is done without changing
the base control. A ControlAdapter is commonly used to custom render for specific platforms like Mobile. In this particular case
the ControlAdapter was used to add a specific behavior to a Control. In this post I will use one adapter to add a Captcha to all WeblogPostCommentForm controls within pontonetpt.com CommunityServer instance.
The Challenge
The ControlAdapter complexity is usually associated with
the complexity/structure of is base control. This case is precisely one of those since base control dynamically load his content (controls) thru several ITemplate. Those of you who already played with ITemplate knows that while it is an excellent option for control composition it also brings to
the table a big issue: “Controls defined within a template are not available for manipulation until they are instantiated inside another control.” While analyzing
the WeblogPostCommentForm control I found that he uses
the ITemplate technique to compose it’s layout and unfortunately I also found that
the template content vary from theme to theme. This could have been a problem but luckily WeblogPostCommentForm control template content always contains a submit button with a well known ID (at least I can assume that there are a well known set of IDs). Using this submit button as anchor it’s possible to add
the Captcha controls in
the correct place. Another important finding was that WeblogPostCommentForm control inherits from
the WrappedFormBase control which is
the base control for all CommunityServer input forms. Knowing this inheritance link
the main goal has changed to became
the creation of a base ControlAdapter that could be extended and customized to allow adding Captcha to: post comments form contact form user creation form. And, with this mind set, I decided to used
the following ControlAdapter base class signature :public abstract class WrappedFormBaseCaptchaAdapter<T> : ControlAdapter where T : WrappedFormBase
{
}Great, but there are still many to do …
Captcha
The Captcha will be assembled with:
A dynamically generated image with a set of random numbers
A TextBox control where
the image number will be inserted
A Validator control to validate whether TextBox numbers match
the image numbers
This is a common Captcha implementation, is not rocket science and don’t bring any additional problem.
The main problem, as told before, is to find
the correct anchor control to ensure a correct Captcha control injection.
The anchor control can vary by:
target control theme
Implementation
To support this dynamic scenario I choose to use
the following implementation:private List<string> _validAnchorIds = null;
protected virtual List<string> ValidAnchorIds
{
get
{
if (this._validAnchorIds == null)
{
this._validAnchorIds = new List<string>();
this._validAnchorIds.Add("btnSubmit");
}
return this._validAnchorIds;
}
}
private Control GetAnchorControl(T wrapper)
{
if (this.ValidAnchorIds == null || this.ValidAnchorIds.Count == 0)
{
throw new ArgumentException("Cannot be null or empty", "validAnchorNames");
}
var q = from anchorId in this.ValidAnchorIds
let anchorControl = CSControlUtility.Instance().FindControl(wrapper, anchorId)
where anchorControl != null
select anchorControl;
return q.FirstOrDefault();
}
I can now, using
the ValidAnchorIds property, configure a set of valid anchor control Ids.
The GetAnchorControl method searches for a valid anchor control within
the set of valid control Ids. Here, some of you may question why to use a LINQ To Objects expression, but
the important here is to notice
the usage of CSControlUtility.Instance().FindControl CommunityServer method. I want to build on top of CommunityServer not to
reinvent the wheel.
Assuming that an anchor control was found, it’s now possible to inject
the Captcha at
the correct place. This not something new, we do this all
the time when creating server controls or adding dynamic controls:protected sealed override void CreateChildControls()
{
base.CreateChildControls();
if (this.IsCaptchaRequired)
{
T wrapper = base.Control as T;
if (wrapper != null)
{
Control anchorControl = GetAnchorControl(wrapper);
if (anchorControl != null)
{
Panel phCaptcha = new Panel {CssClass = "CommonFormField", ID = "Captcha"};
int index = anchorControl.Parent.Controls.IndexOf(anchorControl);
anchorControl.Parent.Controls.AddAt(index, phCaptcha);
CaptchaConfiguration.DefaultProvider.AddCaptchaControls(
phCaptcha,
GetValidationGroup(wrapper, anchorControl));
}
}
}
}
Here you can see a new entity in action: a provider. This is a CaptchaProvider class instance and is only goal is to create
the Captcha itself and do everything else is needed to ensure is correct operation.public abstract class CaptchaProvider : ProviderBase
{
public abstract void AddCaptchaControls(Panel captchaPanel, string validationGroup);
}
You can create your own specific CaptchaProvider class to use different Captcha strategies including
the use of existing Captcha services like ReCaptcha.
Once
the generic ControlAdapter was created became extremely easy to created a specific one. Here is
the specific ControlAdapter for
the WeblogPostCommentForm control:public class WeblogPostCommentFormCaptchaAdapter : WrappedFormBaseCaptchaAdapter<WrappedFormBase>
{
#region Overriden Methods
protected override List<string> ValidAnchorIds
{
get
{
List<string> validAnchorNames = base.ValidAnchorIds;
validAnchorNames.Add("CommentSubmit");
return validAnchorNames;
}
}
protected override string DefaultValidationGroup
{
get { return "CreateCommentForm"; }
}
#endregion Overriden Methods
}
Configuration
This is
the magic step.
Without changing
the original pages and keeping
the application original assemblies untouched we are going to add a new behavior to
the CommunityServer application.
To glue everything together you must follow this steps:
Add
the following configuration to default.browser file:<?xml version='1.0' encoding='utf-8'?>
<browsers>
<browser refID="Default">
<controlAdapters>
<!-- Adapter for
the WeblogPostCommentForm control in order to add
the Captcha and prevent SPAM comments -->
<adapter controlType="CommunityServer.Blogs.Controls.WeblogPostCommentForm" adapterType="NunoGomes.CommunityServer.Components.WeblogPostCommentFormCaptchaAdapter, NunoGomes.CommunityServer" />
</controlAdapters>
</browser>
</browsers>
Add
the following configuration to web.config file:<configuration>
<configSections>
<!-- New section for Captcha providers configuration -->
<section name="communityServer.Captcha" type="NunoGomes.CommunityServer.Captcha.Configuration.CaptchaSection" />
</configSections>
<!-- Configuring a simple Captcha provider -->
<communityServer.Captcha defaultProvider="simpleCaptcha">
<providers>
<add name="simpleCaptcha" type="NunoGomes.CommunityServer.Captcha.Providers.SimpleCaptchaProvider, NunoGomes.CommunityServer"
imageUrl="~/captcha.ashx"
enabled="true"
passPhrase="_YourPassPhrase_"
saltValue="_YourSaltValue_"
hashAlgorithm="SHA1"
passwordIterations="3"
keySize="256"
initVector="_YourInitVectorWithExactly_16_Bytes_"
/>
</providers>
</communityServer.Captcha> <system.web>
<httpHandlers>
<!--
The Captcha Image handler used by
the simple Captcha provider -->
<add verb="GET" path="captcha.ashx" type="NunoGomes.CommunityServer.Captcha.Providers.SimpleCaptchaProviderImageHandler, NunoGomes.CommunityServer" />
</httpHandlers>
</system.web>
<system.webServer>
<handlers accessPolicy="Read, Write, Script, Execute">
<!--
The Captcha Image handler used by
the simple Captcha provider -->
<add verb="GET" name="captcha" path="captcha.ashx" type="NunoGomes.CommunityServer.Captcha.Providers.SimpleCaptchaProviderImageHandler, NunoGomes.CommunityServer" />
</handlers>
</system.webServer>
</configuration>
Conclusion
Building a ControlAdapter can be complex but
the reward is his ability to allows us, thru configuration changes, to modify an application render and/or behavior.
You can see this ControlAdapter in action here and here (anonymous required).
A complete solution is available in “CommunityServer Extensions” Codeplex project.
