ViewFilter - Take 2

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I’ve been asked lately about the use of the ViewFilter mechanism in AspView.

I’ve once written about it briefly here on my blog, and you can see it at http://kenegozi.com/Blog/2007/01/08/introducing-viewfilters.aspx

However, I’ll post another (a bit more realistic) example here.

Scenario: some kind of a CMS thing. You want to present the user with some markup, in both “preview” mode and “Source” modes.

If the server had direct access to the markup in a string literal, things were easy. That usually happens when the markup is to be supplied by an end user, either directly or through a WYSIWYG Html editor. You’d end up with something like:

public interface IContentItem{ public string Markup { get; }}

your view would look like:

...
<h3>Preview:</h3><div><%=view.ContentItem.Markup %> </div><h3>Source:</h3><div><%=Helpers.Html.HtmlEncode(view.ContentItem.Markup) %> </div>...

easy enough.

However, what if the piece of markup that you want to show, has some view-logic, so you have a template generating the markup from an entity? For example, this blog has a view “Posts/One” that gets a Post entity, and fits it into a single post markup, putting the title in a <h4>, tags in <span> with theit title and href, etc.

How can you show the markup source for that?

ViewFilter to the rescue.

In short - A ViewFilter is a way to transform a chunk of a view, using simple manipulations. Do not look for that on other View Engines, as it’s currently an AspView-only feature.

Let’s code our needed filter:

public class HtmlEncodeViewFilter : IViewFilter{ public string ApplyOn(string input) { return HttpUtility.HtmlEncode(input); }}

and in the view:

...&lt;% foreach (Post post in view.Posts) { %&gt;&lt;h3&gt;Preview:&lt;/h3&gt;&lt;subview:.Posts.One post="<%=post %&gt;" > &lt;/subview:.Posts.One&gt;&lt;h3&gt;Source:&lt;/h3&gt;&lt;filter:HtmlEncode&gt; &lt;subview:.Posts.One post="<%=post %&gt;" > &lt;/subview:.Posts.One&gt;&lt;/filter:HtmlEncode&gt;&lt;% } %&gt;

Hey - you won’t even need to create that filter. AspView is supplied with four basic (however useful) filters:

Can you think of more reusable view filters? why not post them here, or better yet, supply a patch to AspView with you filters?

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