Touch To Fill Android Feature

This folder contains the internal parts of the Touch To Fill 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 Touch to Fill component API that intends to change the visible appearance involves all component parts. For example if the API caller requests to show new credentials:

  1. The API caller asks the controller to show a set of credentials.
    1. The controller prepares and filters the credentials for display.
    2. The controller writes the prepared credentials into the model.
  2. The MCP picks up model changes.
    1. The MCP identifies that the CREDENTIAL_LIST property was changed.
    2. The MCP uses a ViewBinder to bind each changed credential to the corresponding view (e.g. a TextView inside a RecyclerView).
  3. The view renders the changed credential list.
    1. The view may apply style, RTL settings 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 PropertyModel as defined in //src/ui/android/java/src/org/chromium/ui/modelutil/. It is build by defining readable and writable properties and constructing a model with them. The properties (and a simple factory method for the model) are located in the static TouchToFillProperties class.

The model contains writable and readable properties.The readable properties are guaranteed to never change for the lifetime of the Touch To Fill component:

  • VIEW_EVENT_LISTENER which is the listener that reacts to view events. The mediator implements this interface.
  • CREDENTIAL_LIST which is the set of displayed credentials. The list itself will be modified (credentials will be added and removed) but the object remains the same which allows to permanently bind it to a list adapter.

The writable properties change over the course of the components lifetime:

  • VISIBLE which will trigger the component to render the bottom sheet or hide it, if it was visible.
  • FORMATTED_URL which is displayed as subtitle for the bottom sheet.

Controller

The controller of this model implements the TouchToFillComponent interface as defined in public/ and contains all logic that affects the component's visual appearance. The controller consists of two parts:

  • TouchToFillCoordinator which implements the public interface and creates all parts of the component (model, mediator, view, etc.) and links them using MCPs.
  • TouchToFillMediator 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.

Additional TouchToFillResourceProvider is used to select resources with any non-trivial logic that determines actual resource file/ID. It also allows overriding the selection logic by providing a different downstream implementation. Upstream implementation is defined in TouchToFillResourceProviderImpl. To support downstream overrides, corresponding build target is listed as dependency in //chrome/android/BUILD.gn, but have no any usages outside of this package.

View

The view contains all parts that are necessary to display the bottom sheet. It consists of two parts:

  • TouchToFillViewBinder which maps model changes to the view. For the Touch To Fill component, the ViewBinder also supports an Adapter that binds changes to the CREDENTIAL_LIST property to the RecyclerView inside the bottom sheet.
  • TouchToFillView which uses the BottomSheetController to create and modify the bottom sheet where credentials are displayed.