Feature: callback for field/model initialisation

[x] feature request

It would be nice to have an initialisation callback before fields are populated. For example:

• In the Repeating Type, when model data exists, the FieldGroups are already populated, before the FieldArrayType implementation’s ngOnit runs. Having a callback would simplify the code. https://stackblitz.com/edit/angular-abr1eg?file=src/app/datatable.type.ts

• In the Repeating Type to populate buttons.

• In the Repeating Type to populate a first row in the model when no model data exists.

Some of this can be done before it is handed over to formly, but I think it also makes sense to have the option to have it as near to the library as possible.

[aitboudad]

good news, I figure-out that there is a way to create the field component instance too early so there a hope to have a such feature out of the box!

[FritzHerbers]

@aitboudad Great, your extension works as expected. It can solve to reduce complexities in the custom type’s code. Thanks a lot.

To use a field config implementation is not my favored one. To use a custom type the app component (by field config) has to provide code which needs to interact with the behaviour of the custom type or even provide the full code for the custom type’s intend.

To overcome this, before handing over the field config to formly an application can call a service which traverses through the field config, modifies the field config for a custom type and also provides the populate code.

The idea of a custom type is to have an interface (by an as simple as possible field config) and a behaviour/semantics. It interacts closely with the formly library and shields of the implementation for it’s users (app component) (and even more the implementation of the formly library).

I was hoping more for a coded solution, extending a populate method in the derived custom type: TypeScript extending example

Are there any drawbacks or implications using such a solution?

The field config implementation can be valuable for specific situations. Would be great to have an additional “coded” solution.

For the time being I will go the above described “using a service” path.