Integrating Go with Android: A Practical Guide

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Author: Xiaoyu Station

Source: http://www.songjiayang.com/posts/go-he-andji-shi-li?from=timeline

Introduction

Seeing this title, you may ask, why run Go on Android, isn’t it good to use Java directly?

Yes, if you have a strong Java team, that’s not a problem, but not all teams are like that. And what I want to emphasize here is the integration of Android and Go, that is, using Go in Android programs rather than writing Android programs entirely in Go.

Some reasons I can think of for using Go in Android:

• The team is familiar with Go and knows little about Java/Android.
• There is already existing Go core code, such as open-source libraries: libp2p, turn/stun libraries, etc.
• The core logic of the SDK of the service is complex and tedious, involving a lot of network or concurrency operations.

Being able to use Go code on Android benefits from Go’s powerful cross-compilation capabilities. So how can we use our Go library on Android? Next, I will explain through a simple example.

Example Tutorial

This example uses a simple dynamic library compiled from Go in an Android program to achieve a simple website speed test.

Idea:

• Cross-compile Go to create a so file supported by the Android platform.
• Use JNA to call the so file in Android.

Dependencies:

• Go
• NDK r20
• JNA 5.4.0

Note: The demonstration environment is Mac.

Writing Go Test Code

Write the core code of speedtester to detect the access speed of any website:

Write CGO code to expose a Perform API function:

Cross-Compiling Dynamic Library

In the previous article on how to cross-compile CGO programs for ARM architecture on Ubuntu, I mentioned how to cross-compile CGO code, only that the platform was Linux at that time. Now we will use a similar method to compile the Android version.

Cross-compiling the Android version of the dynamic library not only requires specifying GCC but also specifying NDK_TOOLCHAIN, so we first need to download the corresponding NDK.

Step 1: Download ndk r20

After decompression, you can see the ndk directory as follows:

Step 2: Compile toolchain

We can use the make-standalone-toolchain.sh script that comes with the NDK to compile a specific toolchain, using the following command:

Parameter explanation:

1. The toolchain parameter indicates the corresponding Android ARCH, arm32 uses arm-linux-androideabi-4.9, arm64 uses aarch64-linux-android-4.9.
2. The platform parameter indicates the corresponding Android API version, 25 corresponds to Android 7.1.1, 26 corresponds to Android 8.0, 27 corresponds to Android 8.1, 28 corresponds to Android 9.0, 29 corresponds to Android 10.0.
3. The install-dir parameter indicates the location where the compiled target toolchain will be stored, which will be used for cross-compiling Go code later.

Step 3: Execute cross-compilation

Use the toolchain just compiled to cross-compile:

At this point, a libspeedtester.so file will be generated in the directory. You can check its information with the file command as follows:

Android Code Integration

Step 1: Create a new project named goandroid using Android Studio.

Step 2: Add jna dependency

Add the dependency in the build.gradle file:

Step 3: Add jna Android platform dependency

Create a new directory called arm64-v8a in the app/libs directory, store libjnidispatch.so and our dynamic library libspeedtester.so files in it, and modify the build.gradle file to add sourceSets:

Note:

1. libjnidispatch file needs to be selected based on different CPU architectures. You can click the link jna/dist to download the corresponding platform’s jar package, extract the jar package, and extract the libjnidispatch file.
2. The names of the newly created directories vary by phone architecture. For example, my arm64 phone is arm64-v8a, which varies by situation.

Step 4: Add a SpeedTester interface to use our libspeedtester.so library

Step 5: Modify the program homepage to call SpeedTester**

Modify the activity_main.xml file to add the following content:

Modify the MainActivity code to use SpeedTester for speed testing.

Step 6: Modify AndroidManifest.xml, enable network permissions

Step 7: Run on a real machine simulation

Program homepage:

Input http://jd.com, click test, and you can see the output results in Logcat:

You can see that the speed test for the website http://jd.com has been printed in the Logcat log, indicating that our Go code has been successfully called in the Android real machine.

Conclusion

Today we demonstrated how to use Go in Android through a simple example of calling a dynamically linked library compiled by Go in an Android program. The process is roughly as follows:

• Select NDK’s make-standalone-toolchain.sh to compile the native environment’s toolchain.
• Use the compiled toolchain to cross-compile the Android system’s dynamic library.
• Use jna in Android to use the dynamic library.

Code reference: https://github.com/songjiayang/go-android

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