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Device Setup for WebView development

[TOC]

As WebView is an Android system component (rather than just an app), WebView imposes additional requirements on the developer workflow. In particular, WebView requires a physical device or emulator with a userdebug or eng Android image. WebView doesn't support development on user builds.

To build WebView, or run WebView's automated tests, you'll need to set up either an emulator or a physical device.

I have a device or emulator. Will it work for development?

You can check which Android image you have on your device with the following:

# If you don't have `adb` in your path, you can source this file to use
# the copy from chromium's Android SDK.
$ source build/android/envsetup.sh

# If this outputs "userdebug" or "eng" then you're OK! If this outputs "user"
# then you must reflash your physical device or configure a new emulator
# following this guide.
$ adb shell getprop ro.build.type
userdebug

# The API level needs to be 29 or higher:
$ adb shell getprop ro.build.version.sdk
29

Emulator (easy way)

*** promo Unless you have a hardware-specific bug, or need to use a pre-release Android version, a physical device is usually unnecessary. An x86 emulator should be easier to setup.

You can generally follow chromium's Android emulator instructions. You should choose a Google APIs image. The AOSP-based image will also work, but imposes additional developer hurdles. Note that you shouldn't use a Google Play image for development purposes because they are user builds, see Why won't a user image work below.

Choose an emulator image which is Android 10 (SDK 29) or higher.

Physical device

Flash a prebuilt image

Googlers can consult internal instructions here.

External contributors can flash a prebuilt userdebug image (based off aosp-main) onto a Pixel device with Android Flash Tool. This requires a browser capable of WebUSB (we recommend the latest Google Chrome stable release).

Choose an build image which is Android 10 (SDK 29) or higher.

Building AOSP yourself (hard way)

*** note This takes significantly longer than the two previous methods, so please strongly consider one of the above first.

Prerequisite: a machine capable of building Android.

Clone an AOSP checkout, picking a branch supported for your device (you'll need a branch above 10.0.0) from the list of branches:

mkdir aosp/ && cd aosp/ && \
  repo init -u 'https://android.googlesource.com/platform/manifest' -b android-<VERSION> && \
  repo sync -c -j<number>

You can obtain binary drivers for Nexus/Pixel devices here. Drivers should match your device and branch. Extract and run the shell script:

# Change the filenames to match your device/branch (this uses "crosshatch" as an
# example)
tar -xvzf /path/to/qcom-crosshatch-pd1a.180720.030-bf86f269.tgz
./extract-qcom-crosshatch.sh # Extracts to the vendor/ folder

You can build AOSP and flash your device with:

source build/envsetup.sh
device="crosshatch" # Change this depending on your device hardware
lunch aosp_${device}-userdebug
make -j<number>

# Flash to device
adb reboot bootloader
fastboot -w flashall

For more information, please defer to official instructions.

Why won't a user image work?

user images have all of Android's security features turned on (and they can't be disabled). In particular, you won't be able to install a locally built WebView:

  • Most user images are release-keys signed, which means local WebView builds can't install over the preinstalled standalone WebView.
  • user images have extra validity checks for the WebView provider package which pose as an obstacle when loading your own locally compiled WebView for debugging purposes.

Both of the above are important security features: these protect users from running malware in the context of WebView (which runs inside the context of apps). Unfortunately, these features break debugging and development so the features are disabled for engineering OS images.