Device Setup for WebView development

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.

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/

# 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

Emulator (easy way)

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.

Physical device

Flash a prebuilt image

Googlers can consult internal instructions here.

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

Building AOSP yourself (hard way)

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 5.0.0) from the list of branches:

mkdir aosp/ && cd aosp/ && \
  repo init -u -b android-9.0.0_r33 && \
  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
./ # Extracts to the vendor/ folder

You can build AOSP and flash your device with:

source build/
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. This blocks development on L-M, since this is the only WebView provider.
  • On N+, although you can install a locally compiled monochrome_{public_}apk, this is not a valid WebView provider. Unlike on userdebug/eng images, the WebView update service performs additional signature checks on user images, only loading code that has been signed by one of the expected signatures—as above, these keys are not available for local builds.

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).