Using Custom Attributes from the Property Control in your Custom Controls

When you write a custom property, you often end up writing a custom control for it too.  Then, when you call that property using the EPiServer Property control, it creates your internal (“inner”) control as part of its controls collection.  Your custom control might create other controls to actually render something.

For instance, when you use the PageLink property from the Property control, the actual control tree looks like this:

• Property
  • PagePropertyReferenceControl
    • Hyperlink

What frustrated me is that I couldn’t figure out how to get a value “down” to the “lower” controls.  I wanted to be able to set random values on the EPiServer Property control (the first level), then access those from my custom control (the second level), to set values on the child controls it creates (the third level).

For instance, I wrote a custom property for “Gravatar Image.”  It displays the Gravatar image for the last editor of the current page.  You drop it on the page using the standard Property control (the first level in the structure shown above).

This creates my custom GravatarImageControl as a child control (the second level).  That, in turn, creates an Image control (the third level).  Like this:

• Property
• GravatarImage
• Image

However, Gravatar lets you send a size parameter in the URL when requesting the image (“?s=50” or something).  I wanted to be able to set this on the EPiServer Property control, and have it be passed down and eventually find its way onto the ImageUrl property of my Image control..

This is not that hard, it turns out.

From inside my GravatarImageControl, I can get a reference to the “owning” Property control:

On that, you’ll find an Attributes collection, from which you can reference anything.  So, I can insert my Property control like this:

And from inside my GravatarImageControl, I can “pick up” that value and use it to affect the Image control I'm creating:

Thanks to Jacob Kahn for helping me figure this out.