緩存網絡資料--Rx和資料庫

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RxJava是響應式程式設計, 在異步處理網絡資料時, 使用廣泛.

我們也可以使用一些Rx的特性, 優雅地緩存網絡資料.

緩存模式: 讀取資料庫, 顯示, 請求資料, 存儲到資料庫, 再更新頁面.

使用Dagger2+Retrofit+Rx的标準組合, 我來講解一下如何使用.

GitHub下載下傳位址

1. 架構

正常項目, 包含跳轉緩存和非緩存頁面, 為了模拟慢速環境, 延遲3秒加載資料.

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    // 跳轉無緩存
    public void gotoNoCache(View view) {
        startActivity(new Intent(this, NocacheActivity.class));
    }

    // 跳轉有緩存
    public void gotoCache(View view) {
        startActivity(new Intent(this, CacheActivity.class));
    }
}
           

2. 無緩存

依賴注入三個關鍵部分, Application/Component/Module.

public class RcApplication extends Application {
    private ApiComponent mApiComponent;

    @Override public void onCreate() {
        super.onCreate();
        mApiComponent = DaggerApiComponent.builder()
                .apiModule(new ApiModule(this)).build();
    }

    public ApiComponent getApiComponent() {
        return mApiComponent;
    }
}
           

@Singleton
@Component(modules = ApiModule.class)
public interface ApiComponent {
    void inject(NocacheActivity activity);

    void inject(CacheActivity activity);
}
           

@Module
public class ApiModule {
    private Application mApplication;

    public ApiModule(Application application) {
        mApplication = application;
    }

    @Provides
    @Singleton
    public Application provideApplication() {
        return mApplication;
    }

    @Provides
    @Singleton GitHubClient provideGitHubClient() {
        return new GitHubClient();
    }

    @Provides ObservableRepoDb provideObservableRepoDb() {
        return new ObservableRepoDb(mApplication);
    }
}
           

子產品提供應用資訊, GitHub的網絡請求, 資料庫.

@Singleton表示單例模式, 全部注入擁有一個執行個體.

頁面, 使用RecyclerView顯示清單資訊, 在加載時顯示ProgressBar.

/**
 * 無緩存Activity
 * <p>
 * Created by wangchenlong on 16/1/18.
 */
public class NocacheActivity extends Activity {

    @Bind(R.id.nocache_rv_list) RecyclerView mRvList;
    @Bind(R.id.nocache_pb_progress) ProgressBar mPbProgress;

    @Inject Application mApplication;
    @Inject GitHubClient mGitHubClient;

    private ListAdapter mListAdapter;

    @Override protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_nocache);
        ButterKnife.bind(this);

        ((RcApplication) getApplication()).getApiComponent().inject(this);

        LinearLayoutManager layoutManager = new LinearLayoutManager(mApplication);
        mRvList.setLayoutManager(layoutManager);

        mListAdapter = new ListAdapter();
        mRvList.setAdapter(mListAdapter);
    }

    @Override protected void onResume() {
        super.onResume();

        // 延遲3秒, 模拟效果
        mGitHubClient.getRepos("SpikeKing")
                .delay(, TimeUnit.SECONDS)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(this::onSuccess, this::onError);

        mPbProgress.setVisibility(View.VISIBLE);
    }

    private void onSuccess(ArrayList<Repo> repos) {
        mListAdapter.setRepos(repos);
        mPbProgress.setVisibility(View.INVISIBLE);
    }

    private void onError(Throwable throwable) {
        mPbProgress.setVisibility(View.INVISIBLE);
    }
}
           

通過觀察可以發現, 長時間顯示白屏會降低使用者體驗. 我來看看緩存模式.

3. 緩存

緩存模式: 讀取資料庫, 顯示, 請求資料, 存儲到資料庫, 再更新頁面.

推薦使用腳本生成資料庫處理類, 使用方式參考, 自動生成DbHelper的腳本.

首頁邏輯.

public class CacheActivity extends Activity {

    @Bind(R.id.cache_rv_list) RecyclerView mRvList; // 清單
    @Bind(R.id.cache_srl_swipe) SwipeRefreshLayout mSrlSwipe; // 重新整理

    @Inject Application mApplication;
    @Inject ObservableRepoDb mRepoDb;
    @Inject GitHubClient mGitHubClient;

    private ListAdapter mListAdapter; // RecyclerView擴充卡

    @Override protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cache);
        ButterKnife.bind(this);

        // 注入類
        ((RcApplication) getApplication()).getApiComponent().inject(this);

        LinearLayoutManager layoutManager = new LinearLayoutManager(mApplication);
        mRvList.setLayoutManager(layoutManager);

        mListAdapter = new ListAdapter();
        mRvList.setAdapter(mListAdapter);

        mSrlSwipe.setOnRefreshListener(this::fetchUpdates);
    }

    @Override protected void onResume() {
        super.onResume();
        mRepoDb.getObservable()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(this::setData);

        fetchUpdates();
        Toast.makeText(mApplication, "正在更新", Toast.LENGTH_SHORT).show();
    }

    // 設定資料, 更新完成會調用
    private void setData(ArrayList<Repo> repos) {
        mListAdapter.setRepos(repos);
        Toast.makeText(mApplication, "更新完成", Toast.LENGTH_SHORT).show();
    }

    private void fetchUpdates() {
        // 延遲3秒, 模拟效果
        mGitHubClient.getRepos("SpikeKing")
                .delay(, TimeUnit.SECONDS)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(mRepoDb::insertRepoList, this::fetchError, this::fetchComplete);
    }

    private void fetchError(Throwable throwable) {
        mSrlSwipe.setRefreshing(false);
    }

    private void fetchComplete() {
        mSrlSwipe.setRefreshing(false);
    }
}
           

資料庫的觀察者

/**
 * Redo的觀察者
 * <p>
 * Created by wangchenlong on 16/1/18.
 */
public class ObservableRepoDb {
    private PublishSubject<ArrayList<Repo>> mPublishSubject; // 發表主題
    private RepoDbHelper mDbHelper; // 資料庫

    public ObservableRepoDb(Context context) {
        mDbHelper = new RepoDbHelper(context);
        mPublishSubject = PublishSubject.create();
    }

    // 傳回觀察者
    public Observable<ArrayList<Repo>> getObservable() {
        Observable<ArrayList<Repo>> firstObservable = Observable.fromCallable(this::getRepoList);
        return firstObservable.concatWith(mPublishSubject); // 連接配接發表主題
    }

    // 從資料庫獲得資料
    private ArrayList<Repo> getRepoList() {
        mDbHelper.openForRead();
        ArrayList<Repo> repos = new ArrayList<>();
        Cursor c = mDbHelper.getAllRepo();
        if (!c.moveToFirst()) {
            return repos; // 傳回空
        }

        do {
            // 添加資料
            repos.add(new Repo(
                    c.getString(RepoDbHelper.REPO_ID_COLUMN_POSITION),
                    c.getString(RepoDbHelper.REPO_NAME_COLUMN_POSITION),
                    c.getString(RepoDbHelper.REPO_DESCRIPTION_COLUMN_POSITION),
                    new Repo.Owner(c.getString(RepoDbHelper.REPO_OWNER_COLUMN_POSITION), "", "", "")));
        } while (c.moveToNext());
        c.close();
        mDbHelper.close();
        return repos;
    }

    // 插入Repo清單
    public void insertRepoList(ArrayList<Repo> repos) {
        mDbHelper.open();
        mDbHelper.removeAllRepo();
        for (Repo repo : repos) {
            mDbHelper.addRepo(
                    repo.getId(),
                    repo.getName(),
                    repo.getDescription(),
                    repo.getOwner().getLogin()
            );
        }
        mDbHelper.close();
        mPublishSubject.onNext(repos); // 會調用更新資料
    }
}
           

這一部分是關鍵, 實作網絡請求同步插入資料庫和更新頁面.

關聯PublishSubject, 在插入資料完成後, 調用綁定觀察者, 更新頁面.

即.concatWith(mPublishSubject)和mPublishSubject.onNext(repos).

Rx在處理網絡請求方面, 确實非常優雅, 值得喜歡完美的人使用.

OK, that’s all! Enjoy it.