java - Android 从 Retrofit 调用获取 LiveData

Question

我正在尝试在我的 Android 项目上使用 Retrofit 获取一些数据，并使用 LiveData 在 ViewModel 和我的 Activity 上更新此数据。

这是我的服务类别:

 class PaymentService {

        private var paymentMethodList = ArrayList<PaymentMethodModel>()
        private val paymentMethodListLiveData = MutableLiveData<List<PaymentMethodModel>>()

        init {
            paymentMethodListLiveData.value = paymentMethodList
        }

        fun fetchPaymentMethods() {
            val retrofit = Retrofit.Builder()
                .baseUrl(SERVICE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build()

            val service = retrofit.create(PaymentClient::class.java)
            val jsonCall = service.getListOfPaymentMethods()
            jsonCall.enqueue(object : Callback<List<PaymentMethodModel>> {
                override fun onResponse(call: Call<List<PaymentMethodModel>>, response: Response<List<PaymentMethodModel>>) {
                    paymentMethodList = (response.body() as ArrayList<PaymentMethodModel>?)!!
                }

                override fun onFailure(call: Call<List<PaymentMethodModel>>, t: Throwable) {
                    //TODO
                }
            })
        }

这是我尝试聆听列表中的更改的地方:

goToNextButton.setOnClickListener {

            paymentMethods = PaymentMethodSelectionViewModel().getAllPaymentMethods()
            paymentMethods!!.observe(viewLifecycleOwner, Observer {
                Log.e("", "")
            })
        }

问题是，到目前为止，我仅第一次使用 0 个元素获取列表，并且在进行其余调用并更新列表后，不会调用此观察者方法。

<小时/>

编辑

class PaymentRepository {

    private val paymentService = PaymentService()

    fun getPaymentMethods(): LiveData<List<PaymentMethodModel>> {
        paymentService.fetchPaymentMethods()
        return paymentService.getPaymentMethods()
    }

}


class PaymentMethodSelectionViewModel: ViewModel() {

    private val paymentRepository = PaymentRepository()
    private val paymentMethods = paymentRepository.getPaymentMethods()

    fun getAllPaymentMethods(): LiveData<List<PaymentMethodModel>> {
        paymentRepository.getPaymentMethods()
        return paymentMethods
    }

}

Answer 1

将您的请求更改为 View 模型

class PaymentMethodSelectionViewModel: ViewModel() {

    //Data
    var paymentMethodList =  MutableLiveData<List<PaymentMethodModel>>()

    fun getAllPayments(){

        val retrofit = Retrofit.Builder()
            .baseUrl(SERVICE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build()

        val service = retrofit.create(PaymentClient::class.java)
        val jsonCall = service.getListOfPaymentMethods()

        jsonCall.enqueue(object : Callback<List<PaymentMethodModel>> {
            override fun onResponse(call: Call<List<PaymentMethodModel>>, response: Response<List<PaymentMethodModel>>) {

                var data: List<PaymentMethodModel>  = (response.body() as ArrayList<PaymentMethodModel>?)!!

               paymentMethodList.value=data


            }

            override fun onFailure(call: Call<List<PaymentMethodModel>>, t: Throwable) {
                //TODO
            }
        })
    }



}

在您的 View ( Activity )中使用

//load
paymentMethodSelectionViewModel.getAllPayments();


//Observers
 paymentMethodSelectionViewModel.paymentMethodList.observe(this,
   Observer { list ->
           // your code
       })

我建议您使用带有coroutines或RXJAVA2的retrofit 2， 检查这个教程

https://medium.com/@amtechnovation/android-architecture-component-mvvm-part-1-a2e7cff07a76

https://medium.com/@saquib3705/consuming-rest-api-using-retrofit-library-with-the-help-of-mvvm-dagger-livedata-and-rxjava2-in-67aebefe031d