Kotlin协程+Flow+Retrofit实现网络请求

• • 导包
  • 代码实现

  	implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
    implementation 'androidx.core:core-ktx:1.6.0'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    //test
    testImplementation 'junit:junit:4.13'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
    //coroutines 协程
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.5.1"
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.5.1"
      //retrofit 2.8.0以上支持协程
    implementation "com.squareup.retrofit2:retrofit:2.9.0"
    implementation "com.squareup.retrofit2:converter-gson:2.9.0"
    implementation "com.squareup.okhttp3:logging-interceptor:4.9.0"
    //util
    implementation "com.blankj:utilcode:1.12.5"

• NewsApi：网络接口

interface NewsApi {

    @GET("toutiao/index?key=5376aaa29d5cc66f87e664bb2b4a078b")
    suspend fun getNewsBean(@Query("type") type:String): NewsBean
}

• NetworkService：接口工具类

object NetworkService {

    private val retrofit = Retrofit.Builder()
        .client(
            OkHttpClient.Builder()
                .callTimeout(5, TimeUnit.SECONDS)
                .addInterceptor(HttpLoggingInterceptor().apply {
                    level = HttpLoggingInterceptor.Level.BODY
                }).build()
        )
        .baseUrl("http://v.juhe.cn/")
        .addConverterFactory(GsonConverterFactory.create())
        .build()

    val newsApi = retrofit.create()

}

• LatestNewsUiState:数据返回类

sealed class LatestNewsUiState {
	//成功
    data class Success(var news: NewsBean?) : LatestNewsUiState()
    //失败
    data class Error(var exception: Throwable?) : LatestNewsUiState()
}

• NewsViewModel：

class NewsViewModel: ViewModel() {
  	private val _uiState = MutableStateFlow(LatestNewsUiState.Success(null))

	//使用Flow来监听，替换LiveData
    val uiState: StateFlow = _uiState

    fun getNewData() {
        viewModelScope.launch {
            latestNews
                .flowOn(Dispatchers.Default)
                .catch { exception ->
                    _uiState.value = LatestNewsUiState.Error(exception)
                }
                .collect { favoriteNews ->
                    _uiState.value = LatestNewsUiState.Success(favoriteNews)
                }
        }
    }

    private val latestNews: Flow = flow {
        if (!NetworkUtils.isConnected()) throw RuntimeException("网络未连接")
        //网络请求
        val latestNews = NetworkService.newsApi.getNewsBean("top")
        //返回结果
        emit(latestNews)
    }


}

• MainActivity

class MainActivity : AppCompatActivity() {
   private val viewModel by viewModels()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        //监听
  lifecycleScope.launch {
            viewModel.uiState.collect { uiState ->
                when (uiState) {
                    is LatestNewsUiState.Success -> result_tv.text = "result is ${uiState.news}"
                    is LatestNewsUiState.Error -> ToastUtils.showShort("error :${uiState.exception?.message}")
                }
            }
        }
    }

// 点击按钮调用
 viewModel.getNewData()
	
}