如何从Activity中的API调用的ViewModel中获取错误？

Question

当我在Android中使用ViewModel时，我在ViewModel类中使用了两个MutableLiveData对象。

var imageList: MutableLiveData<List<HitsItem>> = MutableLiveData()
var errorMessage: MutableLiveData<String> = MutableLiveData()

我想要的是每当API调用errorMessage发生错误时，类似地，当API调用成功时，就设置imageList。

如何在Activity中检查API是否成功，当API调用不成功时，我想在Activity中显示Toast错误消息？

ImageViewModel.kt

fun getImages(): LiveData<List<HitsItem>> {
    imageList = MutableLiveData()
    loadImages()
    return imageList
}

fun loadImages() {
    val api = PexelClient.getClient().create(ApiInterface::class.java)
    val imageObservable = api.images
    imageObservable.subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .map({ result -> result })
        .subscribe(
            Consumer<ImageModel> { this.handleResults(it) },
            Consumer<Throwable> { this.handleError(it) }
        )
}

private fun handleResults(list: ImageModel) {
    imageList.value = list.hits
    errorMessage.value = null
}

private fun handleError(t: Throwable) {
    imageList.value = null
    errorMessage.value = t.message
}

活动

lateinit var imagesViewModel:ImagesViewModel
lateinit var adapter:ImageAdapter

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_mvvm_rx_retrofit)


    rv_images.setHasFixedSize(true)
    rv_images.layoutManager = LinearLayoutManager(this)

    imagesViewModel = ViewModelProviders.of(this).get(ImagesViewModel::class.java)
    imagesViewModel.getImages().observe(this, object : Observer<List<HitsItem>> {
        override fun onChanged(imageList: List<HitsItem>?) {
            if(imageList != null){
                adapter = ImageAdapter(this@MvvmRxRetrofit,imageList)
                rv_images.adapter = adapter
            }
        }
    })


}

Answer 1

1. 创建一个网络响应类 ：

公共类AsyncResponse {

public ResponseStatus responseStatus ;
public Throwable error ;
public JsonElement data ;


AsyncResponse(ResponseStatus responseStatus, JsonElement data ,Throwable error){
    this.responseStatus = responseStatus ;
    this.data = data ;
    this.error = error ;
}

public static AsyncResponse loading(){
    return new AsyncResponse(ResponseStatus.LOADING,null,null);
}

public static AsyncResponse success(JsonElement data){
    return new AsyncResponse(ResponseStatus.SUCCESS,data,null);
}

public static AsyncResponse error(Throwable error){
    return new AsyncResponse(ResponseStatus.ERROR,null,error);
}

}

2. 创建一个枚举类 ：

   公共枚举ResponseStatus {加载，成功，错误}

3. 在viewmodel类中，无论何时收到响应，都只需发布值：

   私有MutableLiveData asyncResponseMutableLiveData = new MutableLiveData <>（）;

   响应成功：

   asyncResponseMutableLiveData.postValue（AsyncResponse.success（））;

   响应错误：

   asyncResponseMutableLiveData.postValue（AsyncResponse.error（new Throwable（e）））;

4.在活动课堂中，观察响应

 mChatDialogViewModel.getResponse().observe(this, new Observer<AsyncResponse>() {
            @Override
            public void onChanged(@Nullable AsyncResponse asyncResponse) {
                if (asyncResponse != null)
                    consumeResponse(asyncResponse);
            }
        });

private void consumeResponse(AsyncResponse asyncResponse) {

        switch (asyncResponse.responseStatus) {

            case LOADING: {
                break;
            }
            case SUCCESS: {

                break;
            }
            case ERROR: {

                break;
            }
            default:
                break;

        }