## Build AOSP
### Build compile environment
1. Install Ubuntu 18.04
2. Install packages: `sudo apt-get install git-core gnupg flex bison build-essential zip curl zlib1g-dev gcc-multilib g++-multilib libc6-dev-i386 lib32ncurses5-dev x11proto-core-dev libx11-dev lib32z1-dev libgl1-mesa-dev libxml2-utils xsltproc unzip fontconfig`
    - https://source.android.com/setup/build/initializing
3. Install Repo
    ```
    mkdir ~/bin
    PATH=~/bin:$PATH
    curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo ;\
    chmod a+x ~/bin/repo ;\
    gpg --recv-key 8BB9AD793E8E6153AF0F9A4416530D5E920F5C65 ;\
    curl https://storage.googleapis.com/git-repo-downloads/repo.asc | gpg --verify - ~/bin/repo
    ```
   - https://source.android.com/setup/develop#installing-repo
4. Download AOSP source
    1. Create folder for AOSP
        ```
        mkdir -p ~/codes/aosp ; cd ~/codes/aosp
        ```   
    2. Setup git
        ```
        git config --global user.name AwinHuang ;\
        git config --global user.email awinhuang@gmail.com
        ```
    3. Download source code
        ```
        repo init -u https://android.googlesource.com/platform/manifest ;\
        repo sync -j8
        ```
        - 如果要切換某一個特定版本可以使用`-b`，例如：`repo init -u https://android.googlesource.com/platform/manifest -b android-10.0.0_r47`。
        - 要知道版本tag可以查看：https://source.android.com/setup/start/build-numbers#source-code-tags-and-builds
5. Build code
    ```
    source build/envsetup.sh ;\
    lunch aosp_arm-eng ;\
    make clobber  ;\
    make -j16
    ```
    - `make clobber`用來刪除build資料夾

### Reference 
- [GitHub - henrymorgen/android-knowledge-system: Android应用开发最强原创知识体系](https://github.com/henrymorgen/android-knowledge-system)
- [Android AOSP基础（二）AOSP源码和内核源码下载 | BATcoder - 刘望舒](http://liuwangshu.cn/framework/aosp/2-download-aosp.html)
- [Android AOSP基础（三）Android系统源码的整编和单编 | BATcoder - 刘望舒](http://liuwangshu.cn/framework/aosp/3-compiling-aosp.html)

## Build kernel
1. Download the code
    ```
    mkdir -p ~/codes/kernel ;\
    cd ~/codes/kernel ;\
    repo init -u https://android.googlesource.com/kernel/manifest ;\
    repo sync -j16
    ```

2. Compile
    ```
    build/build.sh
    ```
    - 如果遇到`Command 'java' not found, but can be installed with:`
        - 依序安裝
            - `sudo apt install default-jre`
            - `sudo apt install openjdk-11-jre-headless`
            - `sudo apt install openjdk-8-jre-headless`
        - 執行 `sudo update-alternatives --config java`
            - 選擇 `/usr/lib/jvm/java-11-openjdk-amd64/bin/java`
        - 再次compile
            - `source build/envsetup.sh`
            - `mm idegen`

3. 產生android.iml和android.ipr
    在source code跟目錄下執行：`development/tools/idegen/idegen.sh`

### Reference 
- [Android kernel源码下载与编译](https://blog.csdn.net/u010164190/article/details/106561022)


## Android App programming
- R的全名：`<PACKAGE_NAME> + .R`，例如package name是`com.awin.testapp`，那全名是`com.awin.testapp.R`。
- AndroidX = Android eXtension
- Layout
    - layout_margin: 物件與其他物件的距離
    - layout_gravity: 物件在容器內的位置（靠左、靠右、置中...）
    - textApperance: 字型大小
- Extensions
    - Android 4.1 沒有自動加入的extension
    - 打開build.gradle，在`plugins`區塊中加入：
        ```
        id 'kotlin-kapt'  
        id 'kotlin-android-extensions'
        ```

- 使用ViewModel & LiveData
    - 確認有 `kotlin-kapt` 這個plugin。
      ![[Pasted image 20210330102148.png]]
    - [Android jetpack所有library](https://developer.android.com/jetpack/androidx/explorer)
    - [Android jetpack - Lifecycle](https://developer.android.com/jetpack/androidx/releases/lifecycle)
    - 從`Declaring dependencies`這區塊複製必要的module
      ![[Pasted image 20210330110411.png]]
      ```
      def lifecycle_version = "2.3.1"

      // ViewModel
      implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
      // LiveData
      implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
      // Annotation processor
      kapt "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"
      ```
      
    - Create a ViewModel
      ```kotlin
      viewModel = ViewModelProvider(this).get(GuessViewModel::class.java)
      ```
      
    - Observe a live data in ViewModel
      ```kotlin
      viewModel.counter.observe(this, Observer {
          counter.setText(it.toString())
      })
      ```
      counter這個變數是包含在ViewModel裡面的live data，我們的資料則是放在counter裡面的「value」。
      所以如果要取用我們的data，則是：`viewModel.counter.value`。
      
- 使用LiveData
    - `val counter = MutableLiveData<Int>()`

### Use ViewBinding
ViewBinding is used to replace Kotlin Synthetics.
1. 在`app/build.gradle`中加入：
    ```
    plugins {  
        ...
        id 'kotlin-parcelize'  <-- Add this
    }
    
    android {
        ...
        buildFeatures {        <-- Add this
            viewBinding true
        }
        ...
    }
    ```
2. 在你的activity裡面
    1. `import <APP_DOMAIN_NAME>.databinding.<ACTIVITY_NAME>Binding`
        假如：APP_DOMAIN_NAME是`com.example.testmultisectioncyclerview`，ACTIVITY_NAME是`ActivityMain`，那就是：
        `import com.example.testmultisectioncyclerview.databinding.ActivityMainBinding`
    2. 用`lateinit`宣告一個變數，變數名稱是activity的名字加上binding，例如`ActivityMain`就是：
        `private lateinit var activityBinding: ActivityMainBinding`
    3. 在`onCreate()`中，就可以用`activityBinding`來取得view與其他元件了：
        ```
        activityBinding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(activityBinding.root) <-- root就是view
        ```

## ADB usage
- [如何透過 adb command line 指令啟動 Android App](https://kkboxsqa.wordpress.com/2014/08/20/%E5%A6%82%E4%BD%95%E9%80%8F%E9%81%8E-adb-command-line-%E6%8C%87%E4%BB%A4%E5%95%9F%E5%8B%95-android-app/)

# MISC
## 教學文
- [Android Template 小技巧 及 寫程式常見的問題](https://www.eeaseries.com/2021/01/android-template.html?m=1)
- [Jetpack Compose 基础知识](https://developers.google.com/codelabs/jetpack-compose-basics?hl=zh-cn#0)
- [一文带你了解适配Android 11分区存储](https://zhuanlan.zhihu.com/p/354632087)