How to show computed property values in EPiServer 8? - episerver

Question

In page edit mode I want to show a read-only text that is based on a page property value. The text could for example be "A content review reminder email will be sent 2015-10-10", where the date is based on the page published date + six months (a value that will be configurable and therefore can change anytime). So far I've tried to accomplish something like this by adding another property on the page.
I've added the property CurrentReviewReminderDate to an InformationPage class we use. In page edit mode the property name is shown, but it doesn't have a value. How do I do to show the value in page edit mode (preferably as a label)?
[CultureSpecific]
[Display(
Name = "Review reminder date",
Description = "On this date a reminder will be sent to the selected mail to remember to verify page content",
Order = 110)]
[Editable(false)]
public virtual string CurrentReviewReminderDate
{
get
{
var daysUntilFirstLevelReminder =
int.Parse(WebConfigurationManager.AppSettings["PageReviewReminder_DaysUntilFirstLevelReminder"]);
if (CheckPublishedStatus(PagePublishedStatus.Published))
{
return StartPublish.AddDays(daysUntilFirstLevelReminder).ToString();
}
return "";
}
set
{
this.SetPropertyValue(p => p.CurrentReviewReminderDate, value);
}
}

Answer 1

EPiServer internally uses the GetPropertyValue method (i.e. the opposite of SetPropertyValue) when retrieving content for the UI.
This makes sense, otherwise your "made-up" value would be stored as the real value whenever the content is saved. This would make fall-back values etc impossible to implement.
So, this is by-design (and quite wisely so) in EPiServer. :)
However, you can customize how properties work by:
Using custom editors by applying UI hints
Modifying property metadata (for example, to display a generated value as a watermark in a textbox without interfering with the actual value being saved)
I could be misunderstanding what you're trying to do, but off the top of my head it looks like a custom editor could be a viable option for your use case?

Answer 2

Another solution would be to hook into the LoadedPage-event and add the value from there. This might not be the best way performance-wise since you need to do a CreateWritableClone, but depending on the site it might not matter.
[InitializableModule]
[ModuleDependency(typeof(EPiServer.Web.InitializationModule))]
public class EventInitialization : IInitializableModule
{
public void Initialize(InitializationEngine context)
{
ServiceLocator.Current.GetInstance<IContentEvents>().LoadedContent += eventRegistry_LoadedContent;
}
void eventRegistry_LoadedContent(object sender, ContentEventArgs e)
{
var p = e.Content as EventPage;
if (p != null)
{
p = p.CreateWritableClone() as EventPage;
p.EventDate = p.StartPublish.AddDays(10);
e.Content = p;
}
}
}