概述
前面介绍了架构组件中Lifcycle、LiveData、ViewModel以及Room的相关知识，在看了谷歌的例子后用kotlin简单写一下实际应用，直接上代码
环境依赖
project的build.gradle文件：
buildscript {
ext.kotlin_version = '1.1.51'
repositories {
google()
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:3.0.1'
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
}
allprojects {
repositories {
google()
jcenter()
}
}
task clean(type: Delete) {
delete rootProject.buildDir
}
module的build.gradle文件：
apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
android {
compileSdkVersion
defaultConfig {
applicationId "example.rxx.kotlin"
minSdkVersion
targetSdkVersion
versionCode
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation"org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
implementation 'com.android.support:appcompat-v7:26.1.0'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.1'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
// ViewModel and LiveData
implementation "android.arch.lifecycle:extensions:1.1.0"
// alternatively, just ViewModel
implementation "android.arch.lifecycle:viewmodel:1.1.0"
// alternatively, just LiveData
implementation "android.arch.lifecycle:livedata:1.1.0"
annotationProcessor "android.arch.lifecycle:compiler:1.1.0"
// Room (use 1.1.0-alpha3 for latest alpha)
implementation "android.arch.persistence.room:runtime:1.0.0"
annotationProcessor "android.arch.persistence.room:compiler:1.0.0"
// Paging
implementation "android.arch.paging:runtime:1.0.0-alpha6"
// Test helpers for LiveData
testImplementation "android.arch.core:core-testing:1.1.0"
// Test helpers for Room
testImplementation "android.arch.persistence.room:testing:1.0.0"
implementation "android.arch.lifecycle:common-java8:1.1.0"
// RxJava support for Room (use 1.1.0-alpha3 for latest alpha)
implementation "android.arch.persistence.room:rxjava2:1.0.0"
// ReactiveStreams support for LiveData
implementation "android.arch.lifecycle:reactivestreams:1.1.0"
}
创建数据源
新建一个user表：
@Entity(tableName = "user")
data class User(@PrimaryKey
@ColumnInfo(name = "userId")
val id: String = UUID.randomUUID().toString(),
@ColumnInfo(name = "userName")
val userName: String)
新建一个UserDao用来操作user表：
@Dao
interface UserDao {
// 配合LiveData使用
@Query("SELECT * FROM user WHERE userId = :id")
fun getUserById(id: String): MutableLiveData<User>
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insertUser(user: User)
@Delete
fun deleteAllUsers()
}
新建一个数据库：
@Database(entities = arrayOf(User::class), version = )
abstract class UsersDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
companion object {
@Volatile private var INSTANCE: UsersDatabase? = null
// 单例
fun getInstance(context: Context) =
INSTANCE ?: synchronized(this) {
INSTANCE ?: buildDatabase(context).also { INSTANCE = it }
}
// 新建数据库
private fun buildDatabase(context: Context) =
Room.databaseBuilder(context.applicationContext,
UsersDatabase::class.java, "Sample.db")
.build()
}
}
创建ViewModel
创建一个ViewModel保存UI数据：
class UserViewModel(private val dataSource: UserDao) : ViewModel() {
companion object {
const val USER_ID = "1"
}
private lateinit var user: MutableLiveData<User>
fun getUser(): MutableLiveData<User> {
return dataSource.getUserById(USER_ID).also { user = it }
}
fun get(): MutableLiveData<User> {
if (user == null) {
user = MutableLiveData()
}
return user
}
fun updateUserName(userName: String): Completable {
return Completable.fromAction {
val newUser = User(USER_ID, userName)
dataSource.insertUser(newUser)
user.value = newUser
}
}
}
自定义一个ViewModelFactory：
class UserViewModelFactory(private val dataSource: UserDao) : ViewModelProvider.Factory {
override fun <T : ViewModel?> create(modelClass: Class<T>): T {
if (modelClass.isAssignableFrom(UserViewModel::class.java)) {
return UserViewModel(dataSource) as T
}
throw IllegalArgumentException("Unknown ViewModel Class")
}
}
提供创建factory的初始化方法：
object Injection {
fun provideUserDataSource(context: Context): UserDao {
val database = UsersDatabase.getInstance(context)
return database.userDao()
}
fun provideViewModelFactory(context: Context): UserViewModelFactory {
val dataSource = provideUserDataSource(context)
return UserViewModelFactory(dataSource)
}
}
在UI层使用（即activity等）：
class MainActivity : AppCompatActivity() {
private lateinit var viewModelFactory: UserViewModelFactory
private lateinit var viewModel: UserViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
viewModelFactory = Injection.provideViewModelFactory(this)
viewModel = ViewModelProviders.of(this, viewModelFactory).get(UserViewModel::class.java)
viewModel.getUser().observe(this, Observer { tv_test.text = it?.userName })
tv_test.setOnClickListener { updateUserName() }
}
private fun updateUserName() {
val userName = "change"
tv_test.isEnabled = false
viewModel.updateUserName(userName)
}
companion object {
private val TAG = MainActivity::class.java.simpleName
}
}
注意： ViewModel中LiveData保持的数据只要有变化，activity中该LiveData的observe就会回调
总结
这就是简单的使用流程，后续会使用MvpClean架构来优化
合理化建议
我们借助Goole组件开发的同时，也可以借助其他三方库来辅助我们开发出更好的应用, 开发者技术前线建议：
- LiveData在某些情况下可使用RxJava2代替。
- Lifecyle等生命周期管理我们可以借助RxLifeCyle。
- 数据层官方推荐使用Room或者Realm，等其他ORM皆可。
- 网络请求库推荐使用Retrofit+Okhttp
- 多层之间解耦合，推荐使用服务发现(Service Locator) 或者依赖注入(DI)，推荐Dagger2。
- Modle和View绑定我们可以使用DataBinding进行快速实现
- 在使用组件架构时候，推荐使用MvpClean，切记不要Mvp，Mvp，Mvp！
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