λ：

• 官网_应用架构指南-MVVM

# android mvvm demo
# 仓库地址: https://github.com/lzyprime/android_demos
# branch: mvvm

git clone -b mvvm https://github.com/lzyprime/android_demos

添加组件

网络：Retrofit + kotlin 协程

我也试过其他框架：Fuel, Ktor Client。但是迫于业务需求，最后保留了Retrofit。如果网络请求比较简单，可以试试这两个框架，由kotlin实现，和协程配合更好。

• Retrofit 官网
• kotlin 协程

lifecycle ktx：ViewModel, LiveData

• 生命周期处理
• Lifecycle
• ViewModel
• LiveData

• androidx.lifecycle:lifecycle-runtime-ktx
• androidx.lifecycle:lifecycle-livedata-ktx
• androidx.lifecycle:lifecycle-viewmodel-ktx
• androidx.activity:activity-ktx

其中activity-ktx目的：

    class MyActivity : AppCompatActivity() {

        override fun onCreate(savedInstanceState: Bundle?) {
            // Create a ViewModel the first time the system calls an activity's onCreate() method.
            // Re-created activities receive the same MyViewModel instance created by the first activity.

            // Use the 'by viewModels()' Kotlin property delegate
            // from the activity-ktx artifact
            val model: MyViewModel by viewModels()
            model.getUsers().observe(this, Observer<List<User>>{ users ->
                // update UI
            })
        }
    }

依赖注入：Hlit

• Hilt
• 依赖注入原理
• Hilt 和 Jetpack集成

数据库：Room

• Room (暂时没需求)

MVVM

0. init

NetUtil

// 网络请求工具

// utils/Net.kt
object Net {
    private const val PROP_BASE_URL = "https://api.unsplash.com/"
    private const val DEBUG_BASE_URL = "https://api.unsplash.com/"
    private val BASE_URL get() = DEBUG_BASE_URL
    private const val ACCESS_KEY = "<access_key unsplash.com>" // 注册https://api.unsplash.com/后拿到

    val retrofit: Retrofit by lazy {
        val okHttpClient = OkHttpClient.Builder()
            .addInterceptor { chain ->
                val url = chain.request().url().newBuilder().addQueryParameter("client_id", ACCESS_KEY).build()
                val request = chain.request().newBuilder().url(url).build()
                chain.proceed(request)
            }.build()

        Retrofit.Builder()
            .baseUrl(BASE_URL)
            .client(okHttpClient)
            .addConverterFactory(GsonConverterFactory.create())
            .build()
    }
}

Response

// 处理网络回包

// data/bean/Response.kt
sealed class Response<out T> {
    data class Success<T>(val data: T) : Response<T>()
    object Failed : Response<Nothing>()
}

Application

// 依赖注入

// UnsplashApplication.kt
@HiltAndroidApp
class UnsplashApplication : Application() {
  ...
}

<!-- AndroidManifest.xml -->

...

    <application
        android:name=".UnsplashApplication"
        ...
        >

1. Model

data bean

// json 解析，变量名与json字段一致

// data/bean/Photo.kt
data class Photo(
    val id: String,
    val created_at: String = "",
    val updated_at: String = "",
    val urls: Urls,
    val likes: Long = 0,
    val liked_by_user: Boolean = false,
    val user: User,
) {
    data class Urls(
        val raw: String,
        val full: String,
        val regular: String,
        val small: String,
        val thumb: String,
    )
}

// data/bean/User.kt
data class User(
    val id:String,
    val updated_at:String = "",
    val username:String="",
    val name:String = "",
    val first_name:String = "",
    val last_name:String = "",
)

retrofit interface

// retrofit 请求interface

// data/api/UnsplashService.kt
interface UnsplashService {
    @GET("photos")
    suspend fun listPhotos(): List<Photo>
}

service module

// hilt 依赖注入，interface无法直接构造，需要通过Module和Provides指明构造方式

// data/api/ServiceModule.kt
@Module
@InstallIn(ApplicationComponent::class)
object ServiceModule {
    private inline fun <reified T> createService(): T = Net.retrofit.create(T::class.java)

    @Singleton
    @Provides
    fun unsplashService():UnsplashService = createService()
}

Model: UnsplashRepository

// model层，提供数据

// data/UnsplashRepository.kt
@Singleton
class UnsplashRepository @Inject constructor(private val service: UnsplashService) {
    suspend fun listPhoto() = try {
        Response.Success(service.listPhotos())
    } catch (_ : Exception){
        Response.Failed
    }
}

2. ViewModel

//viewmodels/ListPhotoViewModel.kt

class ListPhotoViewModel @ViewModelInject constructor(private val repository: UnsplashRepository) :
    ViewModel() {
    val listPhotos:MutableLiveData<List<Photo>> = MutableLiveData()

    fun refreshListPhotos() = viewModelScope.launch {
        when(val res = repository.listPhoto()){
            is Response.Success -> listPhotos.value = res.data
            is Response.Failed -> listPhotos.value = emptyList()
        }
    }
}

3. View

// RecycleView, RefreshBottun, 暴力写法
// MainActivity.kt

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
    private val model: ListPhotoViewModel by viewModels()

    init {
        lifecycleScope.launchWhenCreated {
            model.refreshListPhotos()
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        refreshBtn.setOnClickListener {
            model.refreshListPhotos()
        }

        photoList.layoutManager = GridLayoutManager(this, 2)
        model.listPhotos.observe(this) { photos ->
            photoList.adapter = object : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
                override fun onCreateViewHolder(
                    parent: ViewGroup,
                    viewType: Int
                ): RecyclerView.ViewHolder = object : RecyclerView.ViewHolder(
                    ImageView(parent.context)
                ) {}

                override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
                    val photo = photos[position]

                    with(holder.itemView as ImageView) {
                        Glide.with(this).load(photo.urls.raw).into(this)
                    }
                }

                override fun getItemCount(): Int = photos.size
            }
        }
    }
}