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Please contribute to this document if you think something is missing or could be better.

vab is basically just a wrapper around the Android SDK and NDK. vab is able to both install, locate and orchestrate the tools found inside the distributed development kits.

Welcome - and have a productive time using V and vab!

Contents

Introduction

Android is a, primarily, Java based Operating System - and to be able to develop apps for the majority of devices on the market (2022), the primary option is to target Google-based Android devices.

To be able to develop for Google-based devices, Google provide the Android SDK, and for native developement (C/C++), they provide the Android NDK. Both are currently required to be able to develop Android apps in V.

While the Android OS itself is open source - the SDK and NDK distributed by Google are not. This fact makes everything a bit harder than it ought to be.

So - for us to target the majority, we need the Android SDK and NDK that are both proprietary licensed in such a way that they prevent developers from modifying and re-distributing them - thus forcing developers to use Google's official (rather large) distributions of these development kits.

For historical reasons - the job of locating and using all the tools in the development kits is actually harder than it might appear at first sight since Google tend to move things around, deprecate tools on short, if any, notice and, in general, always be in a kind of "beta" mode when they release the software needed to target and build for the Google flavoured Android OS devices.

To compensate for this they've developed a ~900MiB tool called "Android Studio" to aid developers in developing for their platform... Because of it's huge size, slow compile speeds and the difficulties involved in integrating a satisfying user experience for, at least, V developers - V has chosen to develop a tool that completely eliminate the need to use Android Studio in V development.

With all this in mind vab was born to make life easier for V developers. You can install it by following the instructions in the README.md.

Developing vab

Helping out the development of vab is easy but currently requires you to install vab via git so your repository works as expected.

To install vab via git you need to first remove any existing vab module picked up by V. For example if you previously have installed vab the official way you need to remove vab from your V modules directory.

Once any previous installed versions of vab is uninstalled you should do:

git clone [email protected]:vlang/vab.git ~/.vmodules/vab on Unix-like systems, or git clone [email protected]:vlang/vab.git %USERPROFILE%\.vmodules\vab on Windows.

Once cloned you should be able to build the vab CLI tool like described in README.md.

Developing and Pull Requests in vab follows the same setup and process as described in V's official docs on example workflow for contributing.

The V to Android App Development Cycle

A typical V Android app development cycle will, roughly, include the following steps:

  1. Develop an app in V (using $if android {...} for Android specific code).
  2. Compile the V code to Android compatible C code (v -os android -o code.c ...).
  3. Compile Android compatible C code to a shared library (.so) with a NDK compiler.
  4. Prepare all base files (e.g. AndroidManifest.xml, Java activity sources, etc.) needed for the Android app to be able to start on the device OS.
  5. Compile Java sources to load and bootstrap the shared library + any Java dependencies required.
  6. Package everything up for distribution via an .apk or .aab archive (dex sources, copy native libs etc.).
  7. Sign the packaged .apk/.aab with a keytool.
  8. (Optionally) deploy and/or run the app on an emulator or physical device.
  9. (Optionally) debug the app (via adb logcat ...).

The developer is expected to take care of bullet point 1. while vab will help cover the rest.

Tweaking defaults at compile time

vab tries to strike a balance and be sane and fair about what default values are used. Should the defaults not fit your daily use they can be tweaked via V's powerful compile-time defines (-d ident=value).

The following is a list of values that can be tweaked at compile time:

  • default_app_name via -d vab:default_app_name='V Test App'
  • default_package_id via -d vab:default_package_id='io.v.android'
  • default_activity_name via -d vab:default_activity_name='VActivity'
  • default_package_format via -d vab:default_package_format='apk'
  • default_min_sdk_version = -d vab:default_min_sdk_version=21
  • default_base_files_path via -d vab:default_base_files_path=''

Using vab from the command line

For now please use the Usage section of the README.md and the FAQ.md.

Using vab programmatically

Please keep in mind that using vab programmatically has the same prerequisites as using the vab command line tool. Use vab doctor on the command line to check if all dependencies are met and setup correctly.

You can also invoke the doctor programmatically:

import vab.cli

cli.doctor(...)

On top, it's recommended that you have some experience with Android development already, as some terms and situations can be resolved more quickly with knowledge about the different areas and implications of Android development.

In some situations, calling vab from the command line might not fit a specific project, setup or problem at hand. You usually want more control and flexibility - fear not - this is why vab is also exposed as a module (import vab.xxx).

The most useful modules are the following:

import vab.cli // For easy replication of the `vab` command line tool
import vab.android // For invoking the major steps: compile, package and deploy
import vab.android.sdk // For easy access to tools in the Android SDK
import vab.android.ndk // For easy access to tools in the Android NDK

For general programmatic usage see the relatively small vab.v, that makes up the command line tool. It shows the major steps you need to take, to get from V source code to a running Android app.

Working with native code like C (and implicitly V) on Android can get a little cumbersome when things doesn't fit into the usual boxes, especially because the smallest things can often touch and affect all the different stages in developing an Android application. vab is designed with this in mind, to be able handle each of these stages as flexible and easy as possible.

By using vab as a module you get access to both the high-level operations (compile, package, deploy) as well as fine grained control if you, for example, just want to compile a C file with a specific NDK compiler or locate the path(s) to the SDK or NDK on your host computer.

(See examples for V snippets on how to do certain, popular, tasks).

The high-level program logic for doing most of the work is implemented in the files android/compile.v, android/package.v and android/deploy.v.

If you're in doubt how some call is supposed to work - the source code of these functions is a good place to discover how things, in general, are used and in what order they should be invoked.

They basically contain a function for each major step of the process:

import vab.android

// Compile V source to C source, and C source to a shared library
compile_opt := android.CompileOptions{
    ...
}
android.compile(compile_opt) or { panic(err) }

// Prepare base files, compile Java sources, package everything up in a .apk/.aab
package_opt := android.PackageOptions{
    ...
}
android.package(package_opt) or { panic(err) }

// Deploy the package to an emulator or device
deploy_opt := android.DeployOptions{
    ...
}
android.deploy(deploy_opt) or { panic(err) }

Package base files

"Package base files" (also sometimes referred to as "App skeleton") is a directory containing files and special directory tree structures that vab (and the Java/SDK packaging tools) use as a base for what to include in the resulting APK or AAB package file archive when compilation/building is done.

It is usually found in a project's root next to the executable named "platforms/android".

Both vab itself and/or any extra commands can have a plaforms/android directory in the root of the project that contains files forming the basis of the APK/AAB package being built.

The directories mostly follow the same structure and often provides different entires such as:

  • Custom AndroidManifest.xml tailored for the application/project.
  • Custom Java sources for e.g. the "main" Java activity (under platforms/android/src).
  • Custom resources like strings and icons (under platforms/android/res).

See also fn prepare_package_base(opt PackageOptions) !PackageBase in android/package.v as well as --icon-mipmaps in the FAQ.md.

Package base overrides

Package base files can also be provided/tweaked by user application sources via their platforms/android directory, or via the explicit --package-overrides flag, which will copy all contents of --package-overrides <path> on top of the contents provided as package base files (overwriting any files that may have the same name). This allows for tweaking certain code bases/setups instead of reshipping complete copies of package base files.

Also note that special directories named "java" in root of projects can act as implicit --package-overrides... While this is not ideal, it has historically been a very useful way for modules/apps to provide tweaks to vab's default package base files.

A similar approach (a special jni directory) is being used by the Android NDKs own tooling (ndk-build) for various reasons and can thus be found in other projects where it serves somewhat similar purposes.

vab does not treat any jni directories specially, only the above mentioned to minimize any further confusion.

Examples

The following are some useful examples, please contribute to this section if you think something is missing or could be better. All examples assumes that you have a working install of vab.

Compile V code to Android Compatible C code

It is important to keep in mind that most (if not all?) C libs that control the app window and (OpenGL) acceleration context, usually have framework-like behavior on Android, which means that they usually require full authority over the way they start up and open the NativeActivity which is the entry point for native graphical apps.

This is often the reason why a lot of fiddling is required to get C libs like SDL2, sokol_app and RayLib mixed with V code; All of them want control over how the window/context is opened.

Luckily V allows for outputting code which is agnostic to who or what will open the window.

From the command line, this is basically just invoking the v compiler with the right set of flags for Android:

v -os android -o code.c source.v

A few nice to know flags, in regards to the window/context issue noted above, is especially the -apk and -d no_sokol_app flags.

The former, -apk, tells V that we want to prepare the code for packaging - this implies that code is generated to support V's graphical backend (gg/sokol.app) - this means that V will take control of the window opening and acceleration context.

Sometimes you want your code to compile for other frameworks like e.g. RayLib or SDL2 in this case you'll need the former, -d no_sokol_app flag. This makes sure that V doesn't take control of the initial window opening process leading the way for e.g. SDL2 or RayLib to control it instead.

If you want to do this programmatically you can use the following V code to use vab to produce it.

(For a real life example see the body of this function)

import os
import vab.android

opt := android.CompileOptions{
	work_dir: os.temp_dir()
	// For all options, see link below.
	//
	// You will find that options passed to the command line `vab` is
	// named very closely after the fields in the config structs - to make
	// it as easy as possible to follow the flags around the program.
}
android.compile_v_to_c(opt) or { panic(err) }

android.CompileOptions.

Running the above will produce /tmp/v_android.c, an Android compatible C file that can be compiled by a NDK compiler.

Compile C code to Android shared library (.so)

In the section above we produced Android compatible C code. Now we want to compile that into a shared library that any Java activity can load via System.loadLibrary().

In theory the C code doesn't have to be produced by V - it can be any Android compatible C source code, vab does, however, adjust some compile flags that suit V code better, depending on what you pass in as options to the compile function.

import os
import vab.android

opt := android.CompileOptions{
	work_dir: os.temp_dir()
	// For all options, see link below.
	//
	// no_so_build: true // Use this if you only want to generate object files (.o) and no shared lib (.so)
}
android.compile(opt) or { panic(err) }

android.CompileOptions.

The above produces files in /tmp/build/lib/<arch>/lib<name from opt>.so and /tmp/build/o/<arch>/<source name>.o

If you just want to locate a compiler in the NDK and invoke it, see the next example.

Find and Invoke NDK Compiler Manually

If you just want to locate a compiler from the NDK and invoke it manually, passing everything in yourself - you can use something like the following:

import os
import vab.android.ndk

// Get the path to a C compiler.
//
// `ndk_version` should be the *full* version as indicated by the *directory name* where your NDK resides.
// Available versions detected can be retrieved with:
// `list := ndk.versions_available()`
// If you don't care you can get a default by running:
ndk_version := ndk.default_version()

// Request a C compiler for API level 21 for architecture arm64-v8a from the NDK.
compiler := ndk.compiler(.c, ndk_version, 'arm64-v8a', '21') or { panic(err) }

// Get recommended, Android specific, flags (also used by e.g. Gradle) for the compiler
// Make sure they fit the compiler you're targeting.
compiler_flags := ndk.compiler_flags_from_config(ndk_version,
	arch:         'arm64-v8a'
	lang:         .c
	debug:        true                         // false = if you want production flags (-prod)
	cpp_features: ['no-rtti', 'no-exceptions'] // Special features available for C++ compilers, ignored for C compilers
) or { panic(err) }

// Flatten the flags
flags := compiler_flags.flags.join(' ')

// If you're linking, the linker flags can be obtained via the `ld_flags` field:
// ld_flags := compiler_flags.ld_flags.join(' ')

// Invoke the compiler
os.execute('${compiler} ${flags} -my-other-flags -c input.c -o out.o')

See ndk.v for more functions.

Debugging

A prerequisite to debugging any Android device is a persistent connection to your target device. A persistent connection can be established either by USB-cable or via Wi-Fi.

The supported way of debugging a V-based Android app is via V's println() and eprintln() functions, which are also used when V panics.

By default, V is setup to redirect STDOUT (println()) and STDERR (eprintln()) to the Android device logs.

Technically this is done via the __android_log_vprint() C functions found in <android/log.h>. Interested developers can find the implementation logic in v/thirdparty/android/android.h and the usage in V's builtin println() and eprintln() can be found around the lines in v/vlib/builtin/builtin.c.v#L163.

To access the, extremely verbose, Android device logs, you normally have to use the adb logcat ... command line application with various, at times cryptic, combinations of flags to get a clear overview of your application's output. ADB is also known as the Android Debug Bridge.

If you wish, you can use adb logcat to debug your V app but we recommended to use vab's built-in capabilities instead for a more integrated experience.

To ease the debug process, vab has a few flags and options to help you grab relevant log lines from the otherwise verbose device logs.

The relevant flags are:

  • --log that enables device logging after deployment.
  • --log-raw that enables unfiltered, full device logging after deployment.
  • --log-clear that clears the log buffer on the device before deployment.
  • --log-tag that let you add additional tags to include in the output when using --log.

An example: You have a device connected via USB or Wi-Fi and have enabled developer debugging on the device.

Change working directory to V's install root:

cd ~/path/to/v

Compile, run and stream log output, of a V example app, via vab in one go:

vab --log run examples/gg/mandelbrot.v

vab should now stream all log output from the running app to your terminal, similar to this:

Showing log output from device
Ctrl+C to cancel logging
--------- beginning of main
--------- beginning of system
11-23 13:14:02.742 18291 20348 I v_test_app:  7 threads; 156 ms / frame; scale:    1

Use Ctrl + C in the terminal to stop the output and disconnect from the device, leaving the app running on the device.

Extending vab

Sometimes vab's functionality is just not enough to reach a desired goal. An example of such a thing would be compiling and packaging of a thirdparty library or framework that requires a special way to be build, has a custom main entry function and/or a custom Java Android activity, or other factors that makes it impossible or very cumbersome to get things working with v and/or vab's default functionality.

One way to deal with such problems, without reinventing the wheel, is using vab as a module in combination with the feature that allows users to install and call thirdparty executables.

In vab terms this feature is called extra commands and can be enabled by passing -d vab_allow_extra_commands when compiling vab with v.

Extra commands is a powerful feature that allows users to extend vab with custom functionality via the command-line.

Example extra command

An example of one such extra command is larpon/vab-sdl which makes it easier to compile and run V applications that uses SDL2 via 'vlang/sdl' on Android via vab.

To enable support for this in vab, you can do the following:

  1. Enable extra command support when building vab:
v -d vab_allow_extra_commands ~/.vmodules/vab
  1. Install the larpon/vab-sdl extra command:
vab install extra larpon/vab-sdl
  1. Build your application that uses 'vlang/sdl', for example:
vab sdl ~/.vmodules/sdl/examples/basic_window -o /tmp/sdl_app.apk

Notice how the extra command name vab-sdl is called as vab sdl. You should now be able to install /tmp/sdl_app.apk on your device and run the example without the need to do anything special.

NOTE Use vab doctor to see more detailed information about extra commands including where they are installed and more.

Important notes about extra commands

When you enable and use extra commands you are advised to be careful about installing and running thirdparty extra command software from sources you do not trust.

When you enable and use extra commands it is likely that the developer team can not provide support for any bug or situation that an extra command may have caused.

If possible, always refer to the author, source code and documentation of any extra commands for how to use the commands correctly.