我试图使用存储库和服务定位器制作 mvvm 模式以使用模拟或远程调用，这取决于风格。
现在发生的事情是，在我收到服务器的响应后，我的 liveData 没有更新。所以现在我总是有一个空列表。
我使用这个谷歌示例来尝试制作它。
sample
下面我的代码，使用远程 serviceLocator
感谢您的帮助。
class TestActivity : AppCompatActivity(){
private val viewModel = TestViewModel(ServiceLocator.provideTasksRepository())
private lateinit var binding : TestBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = DataBindingUtil.setContentView(this, R.layout.test)
binding.viewmodel = viewModel
setupRecyclerView()
}
private fun setupRecyclerView() {
binding.viewmodel?.run {
binding.recyclerViewTest.adapter = TestAdapter(this)
}
}
class TestAdapter(private val viewModel : TestViewModel) : ListAdapter<ResponseEntity, TestAdapter.TestViewHolder>(TestDiffCallback()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) = TestViewHolder.from(parent)
override fun onBindViewHolder(holder: TestViewHolder, position: Int) {
val item = getItem(position)
holder.bind(viewModel, item)
}
class TestViewHolder private constructor(val binding: ItemTestBinding) :
RecyclerView.ViewHolder(binding.root) {
fun bind(viewModel: TestViewModel, item: ResponseEntity) {
binding.viewmodel = viewModel
binding.game = item
binding.executePendingBindings()
}
companion object {
fun from(parent: ViewGroup): TestViewHolder {
val layoutInflater = LayoutInflater.from(parent.context)
val binding = ItemTestBinding.inflate(layoutInflater, parent, false)
return TestViewHolder(binding)
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<data>
<import type="android.view.View" />
<import type="androidx.core.content.ContextCompat" />
<variable
name="game"
type="com.test.ResponseEntity" />
<variable
name="viewmodel"
type="com.test.TestViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recycler_view_test"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:items="@{viewmodel.items}"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
class MyRepository(private val testRemoteDataSource: IDataSource) :
ITestRepository {
override suspend fun getList() = testRemoteDataSource.getList()
class TestViewModel(private val testRepository: MyRepository) : ViewModel() {
private var _items = MutableLiveData<List<ResponseEntity>>()
val items: LiveData<List<ResponseEntity>> = _items
init {
refreshList()
}
private fun refreshList() {
viewModelScope.launch {
_items = testRepository.getList()
}
}
object ServiceLocator {
var testRepository: MyRepository? = null
fun provideTasksRepository(): MyRepository {
synchronized(this) {
return testRepository ?: createTestRepository()
}
}
private fun createTestRepository(): MyRepository {
val newRepo = MyRepository(
MyRemoteDataSource(RetrofitClient.apiInterface)
)
testRepository = newRepo
return newRepo
}
class MyRemoteDataSource(private val retroService: IService) :
IDataSource {
private var responseEntityLiveData: MutableLiveData<List<ResponseEntity>> =
MutableLiveData<List<ResponseEntity>>()
override suspend fun getGames(): MutableLiveData<List<ResponseEntity>> {
retroService.getList()
.enqueue(object : Callback<List<ResponseEntity>> {
override fun onFailure(
call: Call<List<ResponseEntity>>,
t: Throwable
) {
responseEntityLiveData.value = emptyList()
}
override fun onResponse(
call: Call<List<ResponseEntity>>,
response: Response<List<ResponseEntity>>
) {
responseEntityLiveData.value = response.body()
}
})
return responseEntityLiveData
}
最佳答案
我的猜测是，将 Coroutines 挂起功能与 Retrofit 和 LiveData 混合会导致一些副作用。
我没有单一的解决方案，但有些要点可以帮助您。
一般来说，我会避免将 LiveData 与挂起函数混合使用。 LiveData 是为 UI/ViewModel 层缓存数据的概念。下层不需要知道像 LiveData 这样的 Android 具体东西。 More information here
在您的存储库或数据源中，可以使用返回单个值的挂起函数或可以发出多个值的协程流。在您的 ViewModel 中，您可以将这些结果映射到您的 LiveData。
数据源
在您的数据源中，您可以使用 suspendCoroutine 或 suspendCancellableCoroutine 将 Retrofit(或任何其他回调接口(interface))与协程连接:
class DataSource(privat val retrofitService: RetrofitService) {
/**
* Consider [Value] as a type placeholder for this example
*/
fun suspend fun getValue(): Result<Value> = suspendCoroutine { continuation ->
retrofitService.getValue().enqueue(object : Callback<Value> {
override fun onFailure(call: Call<List<ResponseEntity>>,
throwable: Throwable) {
continuation.resume(Result.Failure(throwable)))
}
override fun onResponse(call: Call<List<ResponseEntity>>,
response: Response<List<ResponseEntity>>) {
continuation.resume(Result.Success(response.body()))
}
}
}
}
您可以将响应包装为您自己的
Result 类型，例如:sealed class Result<out T> {
/**
* Indicates a success state.
*/
data class Success<T>(val data: T) : Result<T>()
/**
* Indicates an error state.
*/
data class Failure(val throwable: Throwable): Result<Nothing>
}
View 模型
现在在您的
ViewModel 中，您可以启动协程，获取 Result 并将其映射到 LiveData。class TestViewModel(private val dataSource: DataSource) : ViewModel() {
private val _value = MutableLiveData<Value>>()
val value: LiveData<Value> = _value
private val _error = MutableLiveData<String>()
val error: LiveData = _error
init {
getValue()
}
private fun getValue() {
viewModelScope.launch {
val result: Result<Value> = dataSource.getValue()
// check wether the result is of type Success or Failure
when(result) {
is Result.Success -> _value.postValue(result.data)
is Result.Failure -> _error.value = throwable.message
}
}
}
}
关于带有服务定位器的 Android MVVM，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/65379854/