android - java.lang.RuntimeException : Failed to invoke public android. arch.lifecycle.LiveData() 没有参数

Question

我尝试使用 Retrofit 和 Android 架构组件调用 API，但收到此错误

java.lang.RuntimeException: Failed to invoke public android.arch.lifecycle.LiveData() with no args

这是响应的数据类

data class ForecastResult(val city: City, val list: List<Forecast>)

服务接口(interface)

interface ServicesApis { // using dummy data
@GET("data/2.5/forecast/")
fun getForecast(@Query("APPID") APPID: String = "xxxxxxxx"
                , @Query("q") q: String = "94043", @Query("mode") mode: String = "json", @Query("units") units: String = "metric"
                , @Query("cnt") cnt: String = "7"): Call<LiveData<ForecastResult>>
}

和API实现

class WeatherRepoImpl : WeatherRepo {
override fun getDailyForecast(): LiveData<Resource<ForecastResult>> {
    val forecast: MutableLiveData<Resource<ForecastResult>> = MutableLiveData()
    RestAPI.getAPIsrevice().getForecast().enqueue(object : Callback<LiveData<ForecastResult>> {
        override fun onResponse(call: Call<LiveData<ForecastResult>>?, response: Response<LiveData<ForecastResult>>?) {
            when {
                response!!.isSuccessful -> {
                    forecast.postValue(Resource.success(response.body()?.value))
                }
                else -> {
                    val exception = AppException(responseBody = response.errorBody())
                    forecast.postValue(Resource.error(exception))
                }
            }
        }

        override fun onFailure(call: Call<LiveData<ForecastResult>>?, t: Throwable?) {
            val exception = AppException(t)
            forecast.postValue(Resource.error(exception))
        }

    })
    return forecast
}

  }

感谢您的帮助!

Answer 1

从 API 调用中删除 LiveData，并创建 MutableLiveData 对象中包含的 ViewModel 类。

例如:

API 调用定义如下:(删除 LiveData)

   @GET("data/2.5/forecast/")
fun getForecast(@Query("APPID") APPID: String = "xxxxxxxx"
                , @Query("q") q: String = "94043", @Query("mode") mode: String = "json", @Query("units") units: String = "metric"
                , @Query("cnt") cnt: String = "7"): Call<ForecastResult>

创建一个 ViewModel 类:

class YourViewModel: ViewModel() {

    var allObjLiveData = MutableLiveData<YOUROBJECT>()

    fun methodForAPICall(){

        mApiService?.getForecast(.....)?.enqueue(object : Callback<YOUROBJECT>
        {
            override fun onFailure(call: Call<YOUROBJECT>, t: Throwable) {
                allObjLiveData.value = null
            }

            override fun onResponse(call: Call<YOUROBJECT>, response: Response<YOUROBJECT>) {
                allObjLiveData.value=response.body() //Set your Object to live Data
            }

        })
    }
}

现在在您的 Activity 或 fragment 中初始化 ViewModel 类。 并观察实时数据。

    yourViewModelClassObj?.allObjLiveData?.observe(this, Observer {
       //whenever object change this method call every time.
      }
    })

因此您可以在 ViewModel 类中使用 livedata。