Add support for programmatic refresh

[daniel-smith-sonepar]

First, I just started using this control to replace CollectionView and it is awesome - really appreciate the work you have done here!

I have a couple of use cases where I want to perform a refresh of the list without user action but I would like to have the UI update to reflect the refresh is happening. I have a branch where I have implemented this feature and added it to the test app and confirmed it works as expected in iOS and Android. Would you be interested in a PR to add this feature?

[Redth]

I'm curious what this would be doing? How does this differ from the Adapter.InvalidateData() call?

[daniel-smith-sonepar]

The functionality is about updating the Refresh view to show the activity indicator animation in the UI, when Adapter.InvaldiateData() is called programmatically. Obviously if the user performs a pull gesture, that fires Adapter.InvalidateData() and we call the completion action which stop the activity indicator animation. However, if I programmatically call Adapter.InvalidateData(), it does not trigger the refresh views animation indicator to show. Hope that makese sense...let me know.

[Redth]

Ahhh yes I understand what you’re after now.

Definitely makes sense to implement. If you’re up for the challenge I’d welcome the pr.