Writing Custom Formatters

[danroth27]

ASP.NET MVC -> Models -> Writing Custom Formatters

[Luis-Palacios]

any updates or draft for this? i am currently trying to write a text/javascript formatter some docs will be helpful

[danroth27]

Not yet - still on the backlog.

[Rick-Anderson]

@danroth27 can we get an outline of what you want? I'm looking for a community contribution for this. What are the top use cases? I'm guessing text/javascript formatter would be a good example.

[Rick-Anderson]

@danroth27 we really need some guidance ASAP
from @fiyazbinhasan
I managed to write some custom formatters. It was tough cause already all of them are pretty much written by other community members :P. Anyways I wrote a YAML formatter (Input/Output Formatters), Pdf formatter (Output), Xls Formatter (Output). Here is the link to the git repo where you can find them,

I'll write a blog soon. Will keep you notifying. Meanwhile please do check the repo and let me know if I missed anything.

@fiyazbinhasan : Can you write a ReadMe.MD explaining how to build/use the formatters?

@tdykstra has first dibs as co-author, I'm 2nd in line. cc/ @spboyer

See Building Custom Formatters for .Net Core (Yaml Formatters)

[fiyazbinhasan]

@Rick-Anderson readme.md file added :)

[tdykstra]

Proposed outline for the doc

• When to use:

  • There is a particular content type you want to enable that
    a. isn't supported [Edit: Out of Box, that is, in the product] OOB (i.e., not JSON, XML, or plain text) and
    b. You want to enable it in a way that integrates with content negotiation
  • Example use cases
    • Google Protobuf is a binary format that is more efficient than text types.
    • vCard is a text format commonly used for exchanging contact data. The sample app will implement a simple vCard formatter.

• How to create a custom formatter class

  • For text media types (e.g., vcard, json, xml), derive from TextInputFormatter or TextOutputFormatter base class
    • Otherwise, derive from InputFormatter or OutputFormatter base class
  • Note that you can't do constructor DI in a formatter; to access services you need to use the context object that gets passed in to your methods.
  • In the constructor specify valid media types and encodings
    • Add to SupportedMediaTypes collection (e.g., application/vCard)
    • Add to SupportedEncodings collection
  • Override CanReadType/CanWriteType to specify the type you can deserialize into/serialize from (e.g., Contact type for vCard)
    • Note about output formatters: use CanWriteType for design time type, use CanWriteResult for runtime type
  • Override ReadRequestBodyAsync/WriteResponseBodyAsync to do the actual work of deserializing/serializing

• How to configure MVC to use a custom formatter

  • Add the formatter to MvcOptions InputFormatters and/or OutputFormatters collections

[danroth27]

@kichalla Please take a look at the proposed outline. Does the flow seem reasonable? Anything missing?

[kichalla]

Looks good to me.

[tdykstra]

Fixed by #2743