In order to build these examples, add the following two rules to the top-level WORKSPACE file (two directories above this file):

    path="<full path to your Android SDK>",
    api_level=<api level>,

    path="<path to your Android NDK>",

For the android_sdk_repository rule, the value of api_level corresponds to a directory in the SDK containing the specific version of android.jar to compile against. For example, if path = "/Users/xyzzy/Library/Android/sdk" and api_level = 21, then the directory /Users/xyzzy/Library/Android/sdk/platforms/android-21 must exist.

Similarly, for the android_ndk_repository rule, the value of the api_level attribute corresponds to a directory containing the NDK libraries for that API level. For example, if path=/Users/xyzzy/Library/Android/android-ndk-r10e and api_level=21, then you your NDK must contain the directory /Users/xyzzy/Library/Android/android-ndk-r10e/platforms/android-21.

The example android_binary depends on @androidsdk//, so you will need to install the Google Support Libraries version 25.0.0 from the Android SDK Manager.

The following command can be used to build the example app:

bazel build //examples/android/java/bazel:hello_world --java_language_version=8

We also have a nice way to speed up the edit-compile-install development cycle for physical Android devices and emulators: Bazel knows what code changed since the last build, and can use this knowledge to install only the changed code to the device. This currently works with L devices and changes to Java code and Android resources. To try this out, take an android_binary rule and:

  • Set the proguard_specs attribute to [] (the empty list) or just omit it altogether
  • Set the multidex attribute to native
  • Set the dex_shards attribute to a number between 2 and 200. This controls the size of chunks the code is split into. As this number is increased, compilation and installation becomes faster but app startup becomes slower. A good initial guess is 10.
  • Connect your device over USB to your workstation and enable USB debugging on it
  • Run bazel mobile-install <android_binary rule>
  • Edit Java code or Android resources
  • Run bazel mobile-install --incremental <android_binary rule>

Note that if you change anything other than Java code or Android resources (C++ code or something on the device), you must omit the --incremental command line option. Yes, we know that this is also clunky and we are working on improving it.