hello-android-ndk/README.md

This project is a simple demo of how to compile&run native **Aarch64** (or **x86**) binary on a Android device. 

# TL;DR

*.bashrc*
```bash
export ANDROID_NDK="~/bin/android-ndk/r26c-linux"
export ANDROID_SDK_ROOT="~/bin/android_sdk_root"
export PATH="$PATH:$ANDROID_SDK_ROOT/cmdline-tools/latest/bin:$ANDROID_SDK_ROOT/emulator:$ANDROID_SDK_ROOT/platform-tools"
```

# Compile with Android NDK 

- [Download](https://developer.android.com/ndk/downloads) latest version of Android NDK. I'm going go use Linux distribution.
- Set `ANDROID_NDK` Environment Variable to the extracted contents of an archive.
- At this point you should be able to compile the project with `compile.sh` script.

# Run

Technically, if you have Android device with `Development Mode ON` and `adb` binary somewhere on your host PC - you shall be able to install and execute compiled artifact from previous step with help of `run.sh` script. If that is not what you want or have - next sections are for you. 

# Android Emulator without Android Studio

**Directory Structure**
```
$ANDROID_SDK_ROOT/
├── cmdline-tools/
|   └── latest/
|       └── bin/
|           ├── avdmanager
|           ├── sdkmanager
|           ├── ...
|── emulator/
|── platforms/
|   └─ android-23/
|── platform-tools/
|   ├─ adb
|   ├─ fastboot
|   ├─ ...
|── system-images/
|   └─ android-23/
```

## cmdline-tools

- [Download](https://developer.android.com/studio#command-tools) Command line tools only.
- Set  `ANDROID_SDK_ROOT` Environment Variable to the extracted contents of downloaded archive. It is recommended to follow next convention:
  `$ANDROID_SDK_ROOT/cmdline-tools/latest/bin`
- Add it to `PATH`. 
  
## sdkmanager

- List available packages with:
```bash
sdkmanager --list
```

>[!NOTE]
> **QEMU host limitations**<br>
> It looks that Android API 27 is the latest officially supported OS image that is capable of being executed as **Aarch64** Android on **x86_64** host. Later versions of Android can be used only as **x86_64** binaries.

- Install packages for Android API 27 (MARSHMELLOW (6.0), etc) 
```bash
sdkmanager "system-images;android-27;default;arm64-v8a" "platforms;android-27"
```
  
## emulator

- Install emulator and tools: 
```bash
sdkmanager "emulator" "platform-tools"
```

- Add tools to `PATH`: `$ANDROID_SDK_ROOT/emulator`, `$ANDROID_SDK_ROOT/platform-tools`

- Create emulator device: 
```bash
avdmanager --verbose create avd --force \
  --name "pixel_6.0_27" \
  --device "pixel" \
  --package "system-images;android-27;default;arm64-v8a" \
  --tag "default" \
  --abi "arm64-v8a"
``` 

- Start emulator: 
```bash
emulator @pixel_6.27  -qemu -machine virt
```

> [!NOTE] 
> -qemu -machine virt<br>
> This two options are only necessary if you are going to run **Aarch64** Android on a **x86_64** host.  

## adb server

If you see _`access denied`_ error message for `adb` command, run `adb server` with sudo:
```bash
sudo ~/bin/android_sdk_root/platform-tools/adb start-server
```

The command will spawn background `adb server` process, granting necessary access permissions for all subsequent local `adb` commands.