Account Selection Android Feature

This folder contains the internal parts of the Account Selection component. Files, classes and methods defined in here are not meant to be used outside of this package.

This document provides a brief overview of the architecture.

Component structure

This component follows the typical MVC structure that is widely used in Chrome on Android. The MVC structures separates logic from representation:

• The controller creates and connects all subcomponents and performs logic that affects the visual appearance of the component.
• The model keeps all state that affects the visual appearance of the component. Changes made to it are automatically propagated to the view by a Model-Change-Processor (MCP) as defined in //src/ui/android/java/src/org/chromium/ui/modelutil/
• The view is the representation of the component. It enforces styles and is mostly called by a view binder to set mutable properties.

A typical request to the Account Selection component API that intends to change the visible appearance involves all component parts. For example if the API caller requests to show new accounts:

1. The API caller asks the controller to show a set of accounts.
   1. The controller prepares the accounts for display.
   2. The controller writes the prepared accounts into the model.
2. The MCP picks up model changes.
   1. The MCP identifies that the SHEET_ITEMS property was changed.
   2. The MCP uses a ViewBinder to bind each changed account to the corresponding view (e.g. a TextView inside a RecyclerView).
3. The view renders the changed account list.
   1. The view may apply style, and event handlers for click events.

Model

The model holds state and event listeners connected to the view. An MCP automatically notifies listener about any change made to a property. To automate this Observer structure, the model is a ListModel as defined in //src/ui/android/java/src/org/chromium/ui/modelutil/. The items in this model are themselves of type PropertyModel. The properties for these are located in the static AccountSelectionProperties class.

The items in the list can be of three types:

• HEADER: There is only one of these and it represents the header of the view. Contains whether this is for a single or multiple accounts, and the URL for the RP.
• ACCOUNT: One for each account. It contains the account data, favicon, and a click listener.
• CONTINUE_BUTTON: There is only one when we want to show a confirm button.

Controller

The controller of this model implements the AccountSelectionComponent interface as defined in public/ and contains all logic. The controller consists of two parts:

• AccountSelectionCoordinator which implements the public interface and creates all parts of the component (model, mediator, view, etc.) and links them using MCPs.
• AccountSelectionMediator which handles request to the component API and changes the model accordingly. Interactions with the view are typically handled here and either affect the model or notify callers of the component API. This is also responsible for observing the bottom sheet state and notify callers on its dismissal.

View

We use a simple LinearLayout as the top-level view for this component which contains the list view for sheet items. This view is them displayed inside the bottom sheet via AccountSelectionBottomSheetContent. The rest of the logic is split in two parts:

• AccountSelectionViewBinder which maps model changes to the view. This is mainly used by SimpleRecyclerViewAdapter and is responsible to bind changes to the items in the model list to the RecyclerView inside the bottom sheet.
• AccountSelectionBottomSheetContent This is a simple container that implements BottomSheetContent interface and facilitates display of our view inside the BottomSheetController. The bottom sheet controller instance itself is controlled by the mediator to create and modify the bottom sheet where accounts are displayed.