D1DchF8Z

1public class FeedDataSource extends PageKeyedDataSource<Long, Article> {
2
3    private static final String TAG = FeedDataSource.class.getSimpleName();
4    
5  /*  
6   * Step 1: Initialize the restApiFactory.
7   * The networkState and initialLoading variables 
8   * are for updating the UI when data is being fetched
9   * by displaying a progress bar
10   */
11    private RestApiFactory restApiFactory;
12
13    private MutableLiveData networkState;
14    private MutableLiveData initialLoading;
15
16    public FeedDataSource() {
17        this.restApiFactory = RestApiFactory.create();
18      
19        networkState = new MutableLiveData();
20        initialLoading = new MutableLiveData();
21    }
22
23
24    public MutableLiveData getNetworkState() {
25        return networkState;
26    }
27
28    public MutableLiveData getInitialLoading() {
29        return initialLoading;
30    }
31  
32  
33  /*  
34   * Step 2: This method is responsible to load the data initially 
35   * when app screen is launched for the first time.
36   * We are fetching the first page data from the api
37   * and passing it via the callback method to the UI.
38   */  
39    @Override
40    public void loadInitial(@NonNull LoadInitialParams<Long> params,
41                            @NonNull LoadInitialCallback<Long, Article> callback) {
42
43        initialLoading.postValue(NetworkState.LOADING);
44        networkState.postValue(NetworkState.LOADING);
45
46        appController.getRestApi().fetchFeed(QUERY, API_KEY, 1, params.requestedLoadSize)
47                .enqueue(new Callback<Feed>() {
48                    @Override
49                    public void onResponse(Call<Feed> call, Response<Feed> response) {
50                        if(response.isSuccessful()) {
51                            callback.onResult(response.body().getArticles(), null, 2l);
52                            initialLoading.postValue(NetworkState.LOADED);
53                            networkState.postValue(NetworkState.LOADED);
54
55                        } else {
56                            initialLoading.postValue(new NetworkState(NetworkState.Status.FAILED, response.message()));
57                            networkState.postValue(new NetworkState(NetworkState.Status.FAILED, response.message()));
58                        }
59                    }
60
61                    @Override
62                    public void onFailure(Call<Feed> call, Throwable t) {
63                        String errorMessage = t == null ? "unknown error" : t.getMessage();
64                        networkState.postValue(new NetworkState(NetworkState.Status.FAILED, errorMessage));
65                    }
66                });
67    }
68  
69  
70
71    @Override
72    public void loadBefore(@NonNull LoadParams<Long> params,
73                           @NonNull LoadCallback<Long, Article> callback) {
74
75    }
76  
77  
78  /*  
79   * Step 3: This method it is responsible for the subsequent call to load the data page wise.
80   * This method is executed in the background thread
81   * We are fetching the next page data from the api
82   * and passing it via the callback method to the UI.
83   * The "params.key" variable will have the updated value.
84   */
85    @Override
86    public void loadAfter(@NonNull LoadParams<Long> params,
87                          @NonNull LoadCallback<Long, Article> callback) {
88
89        Log.i(TAG, "Loading Rang " + params.key + " Count " + params.requestedLoadSize);
90            
91        networkState.postValue(NetworkState.LOADING);
92
93        appController.getRestApi().fetchFeed(QUERY, API_KEY, params.key, params.requestedLoadSize).enqueue(new Callback<Feed>() {
94            @Override
95            public void onResponse(Call<Feed> call, Response<Feed> response) {
96                /*  
97                 * If the request is successful, then we will update the callback
98                 * with the latest feed items and
99                 * "params.key+1" -> set the next key for the next iteration.
100                 */
101                if(response.isSuccessful()) {
102                    long nextKey = (params.key == response.body().getTotalResults()) ? null : params.key+1;
103                    callback.onResult(response.body().getArticles(), nextKey);
104                    networkState.postValue(NetworkState.LOADED);
105
106                } else networkState.postValue(new NetworkState(NetworkState.Status.FAILED, response.message()));
107            }
108
109            @Override
110            public void onFailure(Call<Feed> call, Throwable t) {
111                String errorMessage = t == null ? "unknown error" : t.getMessage();
112                networkState.postValue(new NetworkState(NetworkState.Status.FAILED, errorMessage));
113            }
114        });
115    }
116}