本篇主要介绍Android系统通过Room进行CRUD操作，以及使用kotlin协程的处理方法。

0. 效果展示

1. 添加依赖

注释使用kapt

apply plugin: 'kotlin-kapt'

1.1 lifecycle

通过这个可以获取其他组建生命周期变化

• 这里注释使用kapt，选着相应的注释依赖

def lifecycle_version = "2.2.0"
// ViewModel
implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
// LiveData
implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
// 基于kotlin-kapt的注释组建
kapt "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"

1.2 Room

• Room就好像spring中的jpa，让CRUD更简单

def room_version = "2.2.5"
implementation "androidx.room:room-runtime:$room_version"// Kotlin 使用 kapt
kapt "androidx.room:room-compiler:$room_version" // optional - Kotlin Extensions and Coroutines support for Room 协程操作库
implementation "androidx.room:room-ktx:$room_version"

1.3 kotlin协程

• 添加coroutines依赖 以及 android协程依赖

// 添加协程安卓库
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.9'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.9'

1.4 数据库表导出

• 配置在defaultConfig中，将room.schemaLocation导出

javaCompileOptions {annotationProcessorOptions {arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]}
}

1.5 dataBinding

• 需要在配置android中激活dataBinding

dataBinding{enabled = true
}

2. 数据表实现

跟spring的配置差不多，model，dao，sersice这些

2.1 创建一个User类

• User类 对应到user_table
• @PrimaryKey设置主键先当于spring的@Id，autoGenerate = true设置自增
• @ColumnInfo(name = "user_name")指定列名

/*** @author: ffzs* @Date: 2020/9/11 下午5:05*/
@Entity(tableName = "user_table")
data class User (@PrimaryKey(autoGenerate = true)var id:Long,@ColumnInfo(name = "user_name")var name:String,@ColumnInfo(name = "email")var email:String
)

2.2 dao实现

• @Dao进行注释
• @Query写法跟jpa基本相同

/*** @author: ffzs* @Date: 2020/9/11 下午5:08*/@Dao
interface UserDao {@Insertsuspend fun insert (user: User):Long@Updatesuspend fun update (user: User):Int@Deletesuspend fun delete (user: User):Int@Query("DELETE FROM user_table")suspend fun deleteAll ():Int@Query("SELECT * FROM user_table")fun findAll ():LiveData<List<User>>@Query("SELECT * FROM user_table WHERE id = :id")suspend fun findById (id:Long):User}

2.3 服务实现

• 主要用来获取数据

class UserRepository(private val dao: UserDao) {val subscribers = dao.findAll()suspend fun insert(user: User):Long{return dao.insert(user)}suspend fun update(user: User):Int{return dao.update(user)}suspend fun delete(user: User) : Int{return dao.delete(user)}suspend fun deleteAll() : Int{return dao.deleteAll()}
}

2.4 RoomDatabase实现

• 通过伴生对象实现单例模式
• entities = [User::class]，需要实现表的类，通过反射生成数据表

/*** @author: ffzs* @Date: 2020/9/11 下午5:15*/
@Database(entities = [User::class], version = 1)
abstract class UserDatabase : RoomDatabase() {abstract val userDao: UserDao// 通过伴生对象实现单例模式companion object {@Volatileprivate var INSTANCE: UserDatabase? = nullfun getInstance(context: Context): UserDatabase {synchronized(this) {var instance = INSTANCEif (instance == null) {instance = Room.databaseBuilder(context.applicationContext,UserDatabase::class.java,"user_table").build()}return instance}}}
}

• 直接通过getInstance方法获取database实例：

UserDatabase.getInstance(application)

3. databinding实现

3.1 实现ViewModel

• 首先需要实现一个ViewModel，用来绑定参数

/*** @author: ffzs* @Date: 2020/9/11 下午4:46*/
class UserViewModel (private val repository: UserRepository): ViewModel(), Observable {@Bindableval inputName = MutableLiveData<String>()@Bindableval inputEmail = MutableLiveData<String>()@Bindableval btnSave = MutableLiveData<String>()@Bindableval btnDel = MutableLiveData<String>()

3.2 activity_main绑定

• 通过layout进行绑定，使用variable进行配置

3.3 关联使用

• 变量关联

• 函数关联，像极了前端的回调
  

3.4 绑定

• 通过下图的方法可以进行绑定，如图所示这里还少一个factory
  

3.5 ViewModelProvider.Factory

/*** @author: ffzs* @Date: 2020/9/11 下午6:43*/
class UserViewModelFactory (private val repository: UserRepository): ViewModelProvider.Factory {override fun <T : ViewModel?> create(modelClass: Class<T>): T {if(modelClass.isAssignableFrom(UserViewModel::class.java)){return UserViewModel(repository) as T}throw IllegalArgumentException("ViewModel类型不匹配")}
}

3.6 设置生命周期的归属

• 指定binding的归属

binding.lifecycleOwner = this

3.7 完整绑定代码

val dao = UserDatabase.getInstance(application).userDao
val repository = UserRepository(dao)
binding = DataBindingUtil.setContentView(this, R.layout.activity_main)
userViewModel = ViewModelProvider(this,UserViewModelFactory(repository)).get(UserViewModel::class.java)
binding.userViewModel = userViewModel

4. RecyclerView实现用户展示

4.1 Holder实现

• 将传入的user信息通过binding写到RecyclerView中
• 以及点击触发效果

/*** @author: ffzs* @Date: 2020/9/11 下午7:12*/
class UserViewHolder (val binding: UserListBinding): RecyclerView.ViewHolder(binding.root){fun bind(user: User, clickListener:(User)->Unit){binding.nameTextView.text = user.namebinding.emailTextView.text = user.emailbinding.listItemLayout.setOnClickListener{clickListener(user)}}
}

4.2 Adapter实现

用来实现RecyclerView状态的更改

• 通过binding生成holder
• onBindViewHolder操作当前位置元素，并执行操作
• getItemCount返回展示数量

/*** @author: ffzs* @Date: 2020/9/11 下午7:11*/
class UserRecyclerViewAdapter(private val clickListener: (User) -> Unit) : RecyclerView.Adapter<UserViewHolder>() {private val userList = ArrayList<User>()override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): UserViewHolder {val layoutInflater = LayoutInflater.from(parent.context)val binding : UserListBinding =DataBindingUtil.inflate(layoutInflater,R.layout.user_list,parent,false)return UserViewHolder(binding)}override fun onBindViewHolder(holder: UserViewHolder, position: Int) {holder.bind(userList[position], clickListener)}override fun getItemCount(): Int {return userList.size}fun setList(users: List<User>){userList.clear()userList.addAll(users)}
}

5. 协程使用

• insert协程写法，直接通过viewModelScope调用协程launch，在代码块中进行操作
• 感觉跟使用reactor有些相似，主要避免阻塞，dao中使用suspend标注异步

private fun insert(subscriber: User) = viewModelScope.launch {val newRowId = repository.insert(subscriber)if (newRowId > -1) {msg.value = Event("$newRowId 成功添加")} else {msg.value = Event("添加出错")}
}

6. debug

6.1 databinding载入失败

配置中需要enable

dataBinding{enabled = true
}

6.2 javax/xml/bind/JAXBException

• java8以上不自带xml bind下图中位置改成java8
• java11写spring还可以，看来写java还有点早
  

7. 源码

github