Android WebView 101

Chrome University 2019

ntfschr@ (he/him)

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(based on a previous talk by boliu@)

Bring the best of Chromium to the Android platform

Sixth platform

Blink’s intent-to-implement / intent-to-ship template:

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Is this feature supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?

What is it?

android.webkit.WebView

A View in Android SDK to display web contents

Hundreds of APIs

Primary use cases

Embedded into app

Browsers

Cordova

Ads

Screenshot missing intentionally

WebView or not?

Add Google account on Android

Gmail email compose

Clicking on a link in Gmail

Clicking on a link in Facebook app

WebView or not?

Add Google account on Android

Gmail email compose

Clicking on a link in Gmail

Clicking on a link in Facebook app

WebView is used by apps on every Android device worldwide

What can it do?

loadUrl() ~ navigate in omnibox

onPageStarted/onPageFinished() callbacks ~ update omnibox while navigating

onReceivedError()/onReceivedHttpError() callbacks ~ error page

What can it do?

evaluateJavascript()/@JavascriptInterface ~ interact with web content

setCookie()/getCookie() ~ interact directly with cookie database

shouldInterceptRequest() ~ modify or intercept arbitrary network requests

Technical guts

Trust model

Browser process is the app process

• Shares code, address space, etc. in the same process
• App is “trusted” and has total control over web contents

Each app is ~equivalent to a different installation of chrome (different data dir)

• Does not share cookies or any other profile data with chrome

Each webview is ~equivalent to a tab in chrome

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WebView is an Android View

Draws synchronously into View system (lots of blocking graphics operations)

Supports Android platform features (smart text selection, autofill)

APIs to control web platform (ex. ServiceWorkerController)

WebView is a Chromium embedder

Embeds content layer, affected by all changes in lower layers

Must support architectural changes (ex. Network Servicification, crashpad)

Chrome's architecture (simplified)

Chrome's low-memory architecture

WebView’s architecture (Android O+)

WebView’s architecture (Android L-N)

Browser (app’s process)

GPU Service (in-process)

Network Service (in-process)

Renderer (in-process)

Blink

V8

Working with WebView

Developer workflow

Workflow almost as easy as Chrome for Android

• Just need an emulator or a userdebug device
• go/webview-docs/quick-start.md (or, //android_webview/docs/)

WebView APK only implements WebView APIs

• Also need an embedding app to test
• go/webview-docs/webview-shell.md

Design Challenges

Weird sizes: small, giant

Weird restrictions: no internet, can’t create popups

Release

Identical release as Chrome on Android

Same version pushed to play store at same time. Same version bundled in Android OS system image.

• Respins for one requires respinning both

Supports the same canary, dev, beta, stable channels

Experiments & metrics

Supports metrics (platform == Android WebView)

Supports field trials (platform == ANDROID_WEBVIEW)

Knows about base::Features and flags in blink, content, etc.

Please remember WebView for your features :)