eWorld.UI - Matt Hawley

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Extending WikiPlex with Custom Renderers

July 30, 2009 13:22 by matthaw

Following up from my prior post on Extending WikiPlex with Custom Macros it's now time to talk about creating custom renderers. When we left off, we had created our title link macro and registered it with WikiPlex. If you had attempted to utilize the new macro in wiki content, you'd get the message "Cannot resolve macro, as no renderers were found." instead of a hyperlink. This was the expected behavior, because while you had identified your new scope via parsing, you were missing that critical link of turning the scope into actual content. Let's take a look at our scenario again to refresh what we're trying to achieve:

 

We would like to integrate WikiPlex into an existing application. The idea is to allow a user contributed area specifically for wiki content. The user should be allowed to use all out-of-the-box macros provided, but also have the ability to have inter-wiki links with the format of [Title of Page]. As you probably realized, there is currently no macro/renderer that will take that content and turn it into a inter-wiki link, so we'll have to extend WikiPlex adding this functionality.

Create a Renderer

Creating a renderer is actually the easiest portion of defining new wiki syntaxes, as it's as complicated as you need to make it. Again, a renderer simply takes in a scope (which is a contextual identifier), processes the content, and returns new content. Let's get started - so in your solution, create a class called TitleLinkRenderer and extend it from WikiPlex.Formatting.IRenderer. You'll then implement the members it requires (Id, CanExpand and Expand). The Id value is simply a string that is used as a key for static renderer registration, so it should be unique (follow the same rule of thumb for naming as the macros).

 

Next, you'll implement the CanExpand method. This method simply takes in a scope name and returns a boolean value indicating if this renderer can expand (or render) the scope successfully. As the formatter is processing all scopes, it goes through the list of renderers in the formatter and finds the first match that can expand that particular scope. There is no guarantee of the order of checking renderers, so always unregister a renderer you're overriding its implementation for. As you'll see below, the CanExpand method is fairly trivial, however should your renderer support a number of scopes, you'll need to change this code to include all of them.

public bool CanExpand(string scopeName)
{
   return scopeName == WikiScopeName.WikiLink;
}

Next, you'll implement the Expand method. This method will take in a scope name, the related input from the wiki source, and html / attribute encoding functions. The reason we're passing in html / attribute encoding functions, is so that you can utilize a consistent encoding scheme across all of the renderers. Out of the box, WikiPlex uses HttpUtility.HtmlEncode and HttpUtility.HtmlAttributeEncode, but by creating & supplying your own formatter, you can change these to use another library (like AntiXss). As previously stated, rendering is as hard as you need it to be. In the sample application example, we're just rendering a link utilizing the ASP.NET MVC UrlHelper (which is supplied via the constructor).

private const string LinkFormat = "<a href=\"{0}\">{1}</a>";

public string Expand(string scopeName, string input,
                     Func<string, string> htmlEncode, 
                     Func<string, string> attributeEncode)
{
   string url = urlHelper.RouteUrl("Default", new { slug = SlugHelper.Generate(input) });
   return string.Format(LinkFormat, attributeEncode(url), htmlEncode(input));
}

And now you have created your renderer, however it will still not be picked up when rendering your wiki content as you need to register the renderer with WikiPlex.

 

Registering a Renderer

Just as registering a macro, you have a static and a dynamic way to register your renderers. If your renderer requires only static dependencies (or no external runtime dependencies), you should opt for statically registering your renderer. To do this, have the following code in your application startup method

Renderers.Register<TitleLinkRenderer>();

When you call the WikiEngine.Render("content"), it will automatically pick up all statically defined renderers and use them when formatting your scopes. As previously stated, if you have external runtime dependencies (like in our example), a little bit of extra work is required when calling WikiEngine.Render - as you'll need to pass in a MacroFormatter instead. However, if you utilize the overload to only take in a formatter, you'll need to union the statically defined renderers with yours.

private MacroFormatter GetFormatter()
{
   var siteRenderers = new IRenderer[] {new TitleLinkRenderer(Url)};
   IEnumerable<IRenderer> allRenderers = Renderers.All.Union(siteRenderers);
   return new MacroFormatter(allRenderers);
}

Now, when you call WikiEngine.Render, you'll utilize the overload that takes in an IFormatter as a parameter. After you've set all of this up, try re-loading your page and you should see your syntax of [Title Link] be converted into the html <a href="/title-link">Title Link</a>.

 

Summary

You now have a new fully functioning macro syntax. Obviously, this example is trivial - but I guarantee if you embed WikiPlex into your application and need any cross-page linking, you'll utilize this macro & renderer. Again, the possibilities are endless with what you can do, so long as you have a syntax, regex, and rendering code - you can allow your users to simply include expansive macros.

 

Download WikiPlex now!

 

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Comments

July 31. 2009 00:27

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Extending WikiPlex with Custom Renderers - eWorld.UI - Matt Hawley

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August 2. 2009 23:42

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Not Rocket Science  » SWiki 0.9 released

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