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。
注释使用kapt
apply plugin: 'kotlin-kapt'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:$lifecycle_version"- Room就好像spring中的jpa，让CRUD更简单
def room_version = "2.2.5"
implementation "androidx.room:room-runtime:$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"- 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'- 配置在
defaultConfig中，将room.schemaLocation导出
javaCompileOptions {
annotationProcessorOptions {
arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
}
}- 需要在配置
android中激活dataBinding
dataBinding{
enabled = true
}跟spring的配置差不多，model，dao，sersice这些
- 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
)@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 {
@Insert
suspend fun insert (user: User):Long
@Update
suspend fun update (user: User):Int
@Delete
suspend 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
}- 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()
}
}- 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 {
@Volatile
private var INSTANCE: UserDatabase? = null
fun getInstance(context: Context): UserDatabase {
synchronized(this) {
var instance = INSTANCE
if (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)- 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 {
@Bindable
val inputName = MutableLiveData<String>()
@Bindable
val inputEmail = MutableLiveData<String>()
@Bindable
val btnSave = MutableLiveData<String>()
@Bindable
val btnDel = MutableLiveData<String>()- 通过layout进行绑定，使用
variable进行配置
- 变量关联
- 函数关联，像极了前端的回调
- 通过下图的方法可以进行绑定，如图所示这里还少一个
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")
}
}- 指定binding的归属
binding.lifecycleOwner = thisval 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- 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.name
binding.emailTextView.text = user.email
binding.listItemLayout.setOnClickListener{
clickListener(user)
}
}
}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)
}
}- 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")
}
}
配置中需要enable
dataBinding{
enabled = true
}- 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
