Improve PlaceHolder API (BETA)

Description

PlaceHolder is used in the Email Actor and RichText Element.

It is template of text, with placeholders like #NAME# #EMAIL#, where NAME is a field name of a form.
And, there are some extra predefined placeholders, like #SUMMARY#, that output a summary of all fields in form.

PlaceHolder

All available placeHolders are

• FormElements of current Form (#FIELDNAME# placeholders will be replaced with actual submitted form values)
• Predefined placeHolder (#SUMMARY#)
• Extra placeHolder by 3rd party developer (provided by custom PlaceHolderProvider)

EditView UI might provide the combobox of available replaceable PlaceHolders, so the editor can choose a placeHolder easily. By default, The EmailActor and the RichTextElement have this combobox.

It is provided by this code

FormsDataStore.GetAvailableReplacablePlaceHolders()

Customized PlaceHolder API

All processing of Placeholder is put in the PlaceHolderService (you can replace it with Dependency Injection - DI).
By default, it activates all instances IPlaceHolderProvider interface, and calls ProcessPlaceHolders().
PlaceHolderService calls available IPlaceHolderProviders in a chain of processing, by Order property. The latter provider is able to alter the previous provider result.

DefaultPlaceHolderProvider is the default implementation of IPlaceHolderProvider:

• It replaces FormElementPlaceHolders with an actual value.
• It provides an extra placeholder, #SUMMARY# .