LiveData Retrofit 数据转换

• 网络响应数据转换为LiveData

class ApiResponse<T>(
    var data: T?,
    var errorCode: Int,
    var errorMsg: String
)

import androidx.lifecycle.LiveData
import retrofit2.CallAdapter
import retrofit2.Retrofit
import java.lang.reflect.Type
import retrofit2.CallAdapter.Factory
import java.lang.reflect.ParameterizedType

class LiveDataCallAdapterFactory : Factory() {
    override fun get(returnType: Type, annotations: Array<Annotation>, retrofit: Retrofit): CallAdapter<*, *>? {
        if (getRawType(returnType) != LiveData::class.java) return null
        //获取第一个泛型类型
        val observableType = getParameterUpperBound(0, returnType as ParameterizedType)
        val rawType = getRawType(observableType)
        if (rawType != ApiResponse::class.java) {
            throw IllegalArgumentException("type must be ApiResponse")
        }
        if (observableType !is ParameterizedType) {
            throw IllegalArgumentException("resource must be parameterized")
        }
        return LiveDataCallAdapter<Any>(observableType)
    }
}

import androidx.lifecycle.LiveData
import retrofit2.Call
import retrofit2.CallAdapter
import retrofit2.Callback
import retrofit2.Response
import java.lang.reflect.Type
import java.util.concurrent.atomic.AtomicBoolean

class LiveDataCallAdapter<T>(private val responseType: Type) : CallAdapter<T, LiveData<T>> {
    override fun adapt(call: Call<T>): LiveData<T> {
        return object : LiveData<T>() {
            private val started = AtomicBoolean(false)
            override fun onActive() {
                super.onActive()
                if (started.compareAndSet(false, true)) {//确保执行一次
                    call.enqueue(object : Callback<T> {
                        override fun onFailure(call: Call<T>, t: Throwable) {
                            val value = ApiResponse<T>(null, -1, t.message ?: "") as T
                            postValue(value)
                        }

                        override fun onResponse(call: Call<T>, response: Response<T>) {
                            postValue(response.body())
                        }
                    })
                }
            }
        }
    }

    override fun responseType() = responseType
}

interface WanApi {
    companion object {
        fun get(): WanApi {
            val clientBuilder = OkHttpClient.Builder()
                .connectTimeout(60, TimeUnit.SECONDS)
            if (BuildConfig.DEBUG) {
                val loggingInterceptor = HttpLoggingInterceptor()
                loggingInterceptor.level = HttpLoggingInterceptor.Level.BODY
                clientBuilder.addInterceptor(loggingInterceptor)
            }
            return Retrofit.Builder()
                .baseUrl("https://www.wanandroid.com/")
                .client(clientBuilder.build())
                .addCallAdapterFactory(LiveDataCallAdapterFactory())
                .addConverterFactory(GsonConverterFactory.create())
                .build()
                .create(WanApi::class.java)
        }
    }
    /**
     * 首页banner
     */
    @GET("banner/json")
    fun bannerList(): LiveData<ApiResponse<List<BannerVO>>>
}