首页手记一步步封装实现自己的网络请求框架 1.0

一步步封装实现自己的网络请求框架 1.0

标签：

Java Android MVVM

一、前言

现如今 Android 领域流行的网络请求框架基本都是用 Retrofit 加 RxJava 来搭配构建的，而以 ViewModel + LiveData + Retrofit + RxJava 来构建请求框架的例子要相对少得多。而本文就是以这四者作为基础组件，介绍如何一步步封装实现自己的网络请求框架（本文实现的例子不仅仅只是一个网络请求框架，同时也是在介绍应用的架构模式），希望对你有所帮助

目前已实现的功能或者说特色包含以下几点：

1、网络请求结果基于观察者模式进行传递，回调操作与 UI 层的生命周期相绑定，避免了内存泄漏

2、数据加载时的 startLoading 与加载结束后的 dismissLoading 操作都是自动调用的，具体实现都封装在基类中。当然，子类也可以实现自己的特定实现。例如，本文提供的例子中，BaseActivity 实现的加载对话框是 ProgressDialog ，子 Activity 可以自主实现其他弹窗形式

3、当网络请求结果为非成功状态时（网络请求失败或者业务请求失败），默认操作是用 Toast 提示失败原因，支持自定义实现失败时的操作

4、逻辑操作与 UI 层相分离，基于观察者模式来实现消息驱动 UI 变化。提供了在 ViewModel 中操作 UI 变化的能力，包括使 Activity / Fragment 弹出对话框、Toast 消息、finishActivity 等 UI 操作，但 ViewModel 不持有 Activity / Fragment 的引用，而是基于消息驱动实现，从而避免了内存泄漏

源码点击这里查看：ReactiveHttp

二、封装 BaseViewModel 与 BaseActivity

ViewModel 与 LiveData 都是 Android Jetpack 架构组件之一。ViewModel 被设计用来存储和管理 UI 相关数据，以便数据能在界面销毁时（比如屏幕旋转）保存数据，而与 ViewModel 相挂钩的 LiveData 是一个用于保存可以被观察的值的数据持有类，且遵循应用组件的生命周期，只有在组件的生命周期处于活跃状态时才会收到数据更新通知

既然是消息驱动，那么自然需要一个用于抽象消息类型的 Event 类

/**
 * 作者：leavesC
 * 时间：2018/9/30 22:17
 * 描述：
 * GitHub：https://github.com/leavesC
 */
public class BaseEvent {

    private int action;

    public BaseEvent(int action) {
        this.action = action;
    }

    public int getAction() {
        return action;
    }

}

public class BaseActionEvent extends BaseEvent {

    public static final int SHOW_LOADING_DIALOG = 1;

    public static final int DISMISS_LOADING_DIALOG = 2;

    public static final int SHOW_TOAST = 3;

    public static final int FINISH = 4;

    public static final int FINISH_WITH_RESULT_OK = 5;

    private String message;

    public BaseActionEvent(int action) {
        super(action);
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

}

BaseActionEvent 即用于向 View 层传递 Action 的 Model，在 ViewModel 通过向 View 层传递不同的消息类型，从而触发相对应的操作。因此，BaseViewModel 需要向子类提供默认的实现

public interface IViewModelAction {

    void startLoading();

    void startLoading(String message);

    void dismissLoading();

    void showToast(String message);

    void finish();

    void finishWithResultOk();

    MutableLiveData<BaseActionEvent> getActionLiveData();

}

/**
 * 作者：leavesC
 * 时间：2018/9/30 22:24
 * 描述：
 * GitHub：https://github.com/leavesC
 */
public class BaseViewModel extends ViewModel implements IViewModelAction {

    private MutableLiveData<BaseActionEvent> actionLiveData;

    protected LifecycleOwner lifecycleOwner;

    public BaseViewModel() {
        actionLiveData = new MutableLiveData<>();
    }

    @Override
    public void startLoading() {
        startLoading(null);
    }

    @Override
    public void startLoading(String message) {
        BaseActionEvent baseActionEvent = new BaseActionEvent(BaseActionEvent.SHOW_LOADING_DIALOG);
        baseActionEvent.setMessage(message);
        actionLiveData.setValue(baseActionEvent);
    }

    @Override
    public void dismissLoading() {
        actionLiveData.setValue(new BaseActionEvent(BaseActionEvent.DISMISS_LOADING_DIALOG));
    }

    @Override
    public void showToast(String message) {
        BaseActionEvent baseActionEvent = new BaseActionEvent(BaseActionEvent.SHOW_TOAST);
        baseActionEvent.setMessage(message);
        actionLiveData.setValue(baseActionEvent);
    }

    @Override
    public void finish() {
        actionLiveData.setValue(new BaseActionEvent(BaseActionEvent.FINISH));
    }

    @Override
    public void finishWithResultOk() {
        actionLiveData.setValue(new BaseActionEvent(BaseActionEvent.FINISH_WITH_RESULT_OK));
    }

    @Override
    public MutableLiveData<BaseActionEvent> getActionLiveData() {
        return actionLiveData;
    }

    void setLifecycleOwner(LifecycleOwner lifecycleOwner) {
        this.lifecycleOwner = lifecycleOwner;
    }

}

那作为消息发送方的 BaseViewModel 的具体实现就完成了，之后是消息的接收方 BaseActivity / BaseFragment

BaseActivity 通过监听 BaseViewModel 中 actionLiveData 的数据变化从而在网络请求开始加载时 startLoading，在加载结束时 dismissLoading

一般一个 Activity 对应一个 ViewModel，少部分情况是会对应多个 ViewModel，因此 initViewModel() 声明为了抽象方法，而 initViewModelList() 默认返回了 null

/**
 * 作者：leavesC
 * 时间：2017/11/29 21:04
 * 描述：
 * GitHub：https://github.com/leavesC
 */
@SuppressLint("Registered")
public abstract class BaseActivity extends AppCompatActivity {

    private ProgressDialog loadingDialog;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        initViewModelEvent();
    }

    protected abstract ViewModel initViewModel();

    protected List<ViewModel> initViewModelList() {
        return null;
    }

    private void initViewModelEvent() {
        List<ViewModel> viewModelList = initViewModelList();
        if (viewModelList != null && viewModelList.size() > 0) {
            observeEvent(viewModelList);
        } else {
            ViewModel viewModel = initViewModel();
            if (viewModel != null) {
                List<ViewModel> modelList = new ArrayList<>();
                modelList.add(viewModel);
                observeEvent(modelList);
            }
        }
    }

    private void observeEvent(List<ViewModel> viewModelList) {
        for (ViewModel viewModel : viewModelList) {
            if (viewModel instanceof IViewModelAction) {
                IViewModelAction viewModelAction = (IViewModelAction) viewModel;
                viewModelAction.getActionLiveData().observe(this, baseActionEvent -> {
                    if (baseActionEvent != null) {
                        switch (baseActionEvent.getAction()) {
                            case BaseActionEvent.SHOW_LOADING_DIALOG: {
                                startLoading(baseActionEvent.getMessage());
                                break;
                            }
                            case BaseActionEvent.DISMISS_LOADING_DIALOG: {
                                dismissLoading();
                                break;
                            }
                            case BaseActionEvent.SHOW_TOAST: {
                                showToast(baseActionEvent.getMessage());
                                break;
                            }
                            case BaseActionEvent.FINISH: {
                                finish();
                                break;
                            }
                            case BaseActionEvent.FINISH_WITH_RESULT_OK: {
                                setResult(RESULT_OK);
                                finish();
                                break;
                            }
                        }
                    }
                });
            }
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        dismissLoading();
    }

    protected void startLoading() {
        startLoading(null);
    }

    protected void startLoading(String message) {
        if (loadingDialog == null) {
            loadingDialog = new ProgressDialog(this);
            loadingDialog.setCancelable(false);
            loadingDialog.setCanceledOnTouchOutside(false);
        }
        loadingDialog.setTitle(message);
        loadingDialog.show();
    }

    protected void dismissLoading() {
        if (loadingDialog != null && loadingDialog.isShowing()) {
            loadingDialog.dismiss();
        }
    }

    protected void showToast(String message) {
        Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
    }

    protected void finishWithResultOk() {
        setResult(RESULT_OK);
        finish();
    }

    protected BaseActivity getContext() {
        return BaseActivity.this;
    }

    protected void startActivity(Class cl) {
        startActivity(new Intent(this, cl));
    }

    public void startActivityForResult(Class cl, int requestCode) {
        startActivityForResult(new Intent(this, cl), requestCode);
    }

    @RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN_MR1)
    protected boolean isFinishingOrDestroyed() {
        return isFinishing() || isDestroyed();
    }

}

三、封装 Retrofit 与 RxJava

在前言中说了，框架默认实现了请求失败时的操作（Toast 提示失败原因），也支持自定义回调接口。因此，需要两个回调接口，一个只包含请求成功时的回调接口，另一个多包含了一个请求失败时的回调接口

/**
 * 作者：leavesC
 * 时间：2018/10/27 20:53
 * 描述：
 * GitHub：https://github.com/leavesC
 */
public interface RequestCallback<T> {

    void onSuccess(T t);

}

public interface RequestMultiplyCallback<T> extends RequestCallback<T> {

    void onFail(BaseException e);

}

此外，为了在网络请求成功但业务逻辑请求失败时（例如，请求参数缺失、Token失效等），可以抛出详细的失败信息，需要自定义 BaseException

public class BaseException extends RuntimeException {

    private int errorCode = HttpCode.CODE_UNKNOWN;

    public BaseException() {
    }

    public BaseException(int errorCode, String errorMessage) {
        super(errorMessage);
        this.errorCode = errorCode;
    }

    public int getErrorCode() {
        return errorCode;
    }

}

实现具体的异常类

public class ParamterInvalidException extends BaseException {

    public ParamterInvalidException() {
        super(HttpCode.CODE_PARAMETER_INVALID, "参数有误");
    }

}

public class TokenInvalidException extends BaseException {

    public TokenInvalidException() {
        super(HttpCode.CODE_TOKEN_INVALID, "Token失效");
    }

}

···

为了提升性能，Retrofit 一般是设计成单例模式。为了应对应用中 BaseUrl 可能有多个的情况（本文提供的Demo就是如此），此处使用 Map 来存储多个 Retrofit 实例

/**
 * 作者：leavesC
 * 时间：2018/10/26 23:11
 * 描述：
 * GitHub：https://github.com/leavesC
 */
public class RetrofitManagement {

    private static final long READ_TIMEOUT = 6000;

    private static final long WRITE_TIMEOUT = 6000;

    private static final long CONNECT_TIMEOUT = 6000;

    private final Map<String, Object> serviceMap = new ConcurrentHashMap<>();

    private RetrofitManagement() {

    }

    public static RetrofitManagement getInstance() {
        return RetrofitHolder.retrofitManagement;
    }

    private static class RetrofitHolder {
        private static final RetrofitManagement retrofitManagement = new RetrofitManagement();
    }

    private Retrofit createRetrofit(String url) {
        OkHttpClient.Builder builder = new OkHttpClient.Builder()
                .readTimeout(READ_TIMEOUT, TimeUnit.MILLISECONDS)
                .writeTimeout(WRITE_TIMEOUT, TimeUnit.MILLISECONDS)
                .connectTimeout(CONNECT_TIMEOUT, TimeUnit.MILLISECONDS)
                .addInterceptor(new HttpInterceptor())
                .addInterceptor(new HeaderInterceptor())
                .addInterceptor(new FilterInterceptor())
                .retryOnConnectionFailure(true);
        if (BuildConfig.DEBUG) {
            HttpLoggingInterceptor httpLoggingInterceptor = new HttpLoggingInterceptor();
            httpLoggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
            builder.addInterceptor(httpLoggingInterceptor);
            builder.addInterceptor(new ChuckInterceptor(ContextHolder.getContext()));
        }
        OkHttpClient client = builder.build();
        return new Retrofit.Builder()
                .client(client)
                .baseUrl(url)
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();
    }

    <T> ObservableTransformer<BaseResponseBody<T>, T> applySchedulers() {
        return observable -> observable.subscribeOn(Schedulers.io())
                .unsubscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .flatMap(result -> {
                    switch (result.getCode()) {
                        case HttpCode.CODE_SUCCESS: {
                            return createData(result.getData());
                        }
                        case HttpCode.CODE_TOKEN_INVALID: {
                            throw new TokenInvalidException();
                        }
                        case HttpCode.CODE_ACCOUNT_INVALID: {
                            throw new AccountInvalidException();
                        }
                        default: {
                            throw new ServerResultException(result.getCode(), result.getMsg());
                        }
                    }
                });
    }


    private <T> Observable<T> createData(T t) {
        return Observable.create(new ObservableOnSubscribe<T>() {
            @Override
            public void subscribe(ObservableEmitter<T> emitter) {
                try {
                    emitter.onNext(t);
                    emitter.onComplete();
                } catch (Exception e) {
                    emitter.onError(e);
                }
            }
        });
    }

    <T> T getService(Class<T> clz) {
        return getService(clz, HttpConfig.BASE_URL_WEATHER);
    }

    <T> T getService(Class<T> clz, String host) {
        T value;
        if (serviceMap.containsKey(host)) {
            Object obj = serviceMap.get(host);
            if (obj == null) {
                value = createRetrofit(host).create(clz);
                serviceMap.put(host, value);
            } else {
                value = (T) obj;
            }
        } else {
            value = createRetrofit(host).create(clz);
            serviceMap.put(host, value);
        }
        return value;
    }

}

此外还需要一个自定义的 Observer 来对数据请求结果进行自定义回调

/**
 * 作者：leavesC
 * 时间：2018/10/27 20:52
 * 描述：
 * GitHub：https://github.com/leavesC
 */
public class BaseSubscriber<T> extends DisposableObserver<T> {

    private BaseViewModel baseViewModel;

    private RequestCallback<T> requestCallback;

    public BaseSubscriber(BaseViewModel baseViewModel) {
        this.baseViewModel = baseViewModel;
    }

    BaseSubscriber(BaseViewModel baseViewModel, RequestCallback<T> requestCallback) {
        this.baseViewModel = baseViewModel;
        this.requestCallback = requestCallback;
    }

    @Override
    public void onNext(T t) {
        if (requestCallback != null) {
            requestCallback.onSuccess(t);
        }
    }

    @Override
    public void onError(Throwable e) {
        e.printStackTrace();
        if (requestCallback instanceof RequestMultiplyCallback) {
            RequestMultiplyCallback callback = (RequestMultiplyCallback) requestCallback;
            if (e instanceof BaseException) {
                callback.onFail((BaseException) e);
            } else {
                callback.onFail(new BaseException(HttpCode.CODE_UNKNOWN, e.getMessage()));
            }
        } else {
            if (baseViewModel == null) {
                Toast.makeText(ContextHolder.getContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
            } else {
                baseViewModel.showToast(e.getMessage());
            }
        }
    }

    @Override
    public void onComplete() {

    }

}

四、BaseRemoteDataSource 与 BaseRepo

上文所介绍的 RequestCallback、RetrofitManagement 与 BaseSubscriber 还是一个个单独的个体，还需要一个链接器来将之串起来，这个链接器的实现类即 BaseRemoteDataSource

在这里，对 BaseRemoteDataSource 的定位是将之当成一个接口实现者，即在 RemoteDataSource 中实际调用各个请求接口，并通过 RxJava 来控制 loading 弹出以及销毁的时机

一般而言，BaseRemoteDataSource 的实现类中声明的是具有相关逻辑的接口。例如，对于登录模块，可声明一个 LoginDataSource，对于设置模块，可以声明一个 SettingsDataSource

/**
 * 作者：leavesC
 * 时间：2018/10/27 7:42
 * 描述：
 * GitHub：https://github.com/leavesC
 */
public abstract class BaseRemoteDataSource {

    private CompositeDisposable compositeDisposable;

    private BaseViewModel baseViewModel;

    public BaseRemoteDataSource(BaseViewModel baseViewModel) {
        this.compositeDisposable = new CompositeDisposable();
        this.baseViewModel = baseViewModel;
    }

    protected <T> T getService(Class<T> clz) {
        return RetrofitManagement.getInstance().getService(clz);
    }

    protected <T> T getService(Class<T> clz, String host) {
        return RetrofitManagement.getInstance().getService(clz, host);
    }

    private <T> ObservableTransformer<BaseResponseBody<T>, T> applySchedulers() {
        return RetrofitManagement.getInstance().applySchedulers();
    }

    protected <T> void execute(Observable observable, RequestCallback<T> callback) {
        execute(observable, new BaseSubscriber<>(baseViewModel, callback), true);
    }

    protected <T> void execute(Observable observable, RequestMultiplyCallback<T> callback) {
        execute(observable, new BaseSubscriber<>(baseViewModel, callback), true);
    }

    public void executeWithoutDismiss(Observable observable, Observer observer) {
        execute(observable, observer, false);
    }

    private void execute(Observable observable, Observer observer, boolean isDismiss) {
        Disposable disposable = (Disposable) observable
                .throttleFirst(500, TimeUnit.MILLISECONDS)
                .subscribeOn(Schedulers.io())
                .unsubscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .compose(applySchedulers())
                .compose(isDismiss ? loadingTransformer() : loadingTransformerWithoutDismiss())
                .subscribeWith(observer);
        addDisposable(disposable);
    }

    private void addDisposable(Disposable disposable) {
        compositeDisposable.add(disposable);
    }

    public void dispose() {
        if (!compositeDisposable.isDisposed()) {
            compositeDisposable.dispose();
        }
    }

    private void startLoading() {
        if (baseViewModel != null) {
            baseViewModel.startLoading();
        }
    }

    private void dismissLoading() {
        if (baseViewModel != null) {
            baseViewModel.dismissLoading();
        }
    }

    private <T> ObservableTransformer<T, T> loadingTransformer() {
        return observable -> observable
                .subscribeOn(AndroidSchedulers.mainThread())
                .unsubscribeOn(AndroidSchedulers.mainThread())
                .observeOn(AndroidSchedulers.mainThread())
                .doOnSubscribe(disposable -> startLoading())
                .doFinally(this::dismissLoading);
    }

    private <T> ObservableTransformer<T, T> loadingTransformerWithoutDismiss() {
        return observable -> observable
                .subscribeOn(AndroidSchedulers.mainThread())
                .unsubscribeOn(AndroidSchedulers.mainThread())
                .observeOn(AndroidSchedulers.mainThread())
                .doOnSubscribe(disposable -> startLoading());
    }

}

除了 BaseRemoteDataSource 外，还需要一个 BaseRepo。对 BaseRepo 的定位是将其当做一个接口调度器，其持有 BaseRemoteDataSource 的实例并中转 ViewModel 的接口调用请求，并可以在 BaseRepo 分担一部分数据处理逻辑

/**
 * 作者：leavesC
 * 时间：2018/10/27 21:10
 * 描述：
 * GitHub：https://github.com/leavesC
 */
public class BaseRepo<T> {

    protected T remoteDataSource;

    public BaseRepo(T remoteDataSource) {
        this.remoteDataSource = remoteDataSource;
    }

}

这样，ViewModel 不关心接口的实际调用实现，方便以后更换 BaseRemoteDataSource 的实现方式，且将一部分的数据处理逻辑放到了 BaseRepo ，有利于逻辑的复用

五、实践操作（1）-请求天气数据

上文讲了一些基础组件的逻辑实现以及对其的定位，此小节就以一个请求天气数据的接口为例，来介绍如何具体实现一个网络请求的整体流程

首先是声明接口

public interface ApiService {

    @Headers({HttpConfig.HTTP_REQUEST_TYPE_KEY + ":" + HttpConfig.HTTP_REQUEST_WEATHER})
    @GET("onebox/weather/query")
    Observable<BaseResponseBody<Weather>> queryWeather(@Query("cityname") String cityName);

}

增加的头部信息是为了标明该接口的请求类型，因为本文作为 demo 的几个接口所用到的 baseUrl 以及 请求key 并不相同，因此通过声明头部来为接口动态指定请求参数，而这就需要用到 Retrofit 的拦截器了

public class FilterInterceptor implements Interceptor {

    @NonNull
    @Override
    public Response intercept(@NonNull Chain chain) throws IOException {
        Request originalRequest = chain.request();
        HttpUrl.Builder httpBuilder = originalRequest.url().newBuilder();
        Headers headers = originalRequest.headers();
        if (headers != null && headers.size() > 0) {
            String requestType = headers.get(HttpConfig.HTTP_REQUEST_TYPE_KEY);
            if (!TextUtils.isEmpty(requestType)) {
                switch (requestType) {
                    case HttpConfig.HTTP_REQUEST_WEATHER: {
                        httpBuilder.addQueryParameter(HttpConfig.KEY, HttpConfig.KEY_WEATHER);
                        break;
                    }
                    case HttpConfig.HTTP_REQUEST_QR_CODE: {
                        httpBuilder.addQueryParameter(HttpConfig.KEY, HttpConfig.KEY_QR_CODE);
                        break;
                    }
                    case HttpConfig.HTTP_REQUEST_NEWS: {
                        httpBuilder.addQueryParameter(HttpConfig.KEY, HttpConfig.KEY_NEWS);
                        break;
                    }
                }
            }
        }
        Request.Builder requestBuilder = originalRequest.newBuilder()
                .removeHeader(HttpConfig.HTTP_REQUEST_TYPE_KEY)
                .url(httpBuilder.build());
        return chain.proceed(requestBuilder.build());
    }

}

声明 BaseRemoteDataSource 的实现类 WeatherDataSource

public class WeatherDataSource extends BaseRemoteDataSource implements IWeatherDataSource {

    public WeatherDataSource(BaseViewModel baseViewModel) {
        super(baseViewModel);
    }

    @Override
    public void queryWeather(String cityName, RequestCallback<Weather> responseCallback) {
        execute(getService(ApiService.class).queryWeather(cityName), responseCallback);
    }

}

声明 BaseRepo 的实现类 WeatherRepo

public class WeatherRepo extends BaseRepo<IWeatherDataSource> {

    public WeatherRepo(IWeatherDataSource remoteDataSource) {
        super(remoteDataSource);
    }

    public MutableLiveData<Weather> queryWeather(String cityName) {
        MutableLiveData<Weather> weatherMutableLiveData = new MutableLiveData<>();
        remoteDataSource.queryWeather(cityName, new RequestCallback<Weather>() {
            @Override
            public void onSuccess(Weather weather) {
                weatherMutableLiveData.setValue(weather);
            }
        });
        return weatherMutableLiveData;
    }

}

还需要一个 WeatherViewModel，View 层通过调用 queryWeather() 方法在请求成功时触发 weatherLiveData 更新数据，View 层已事先监听 weatherLiveData，并在数据更新时就可以立即收到最新数据

public class WeatherViewModel extends BaseViewModel {

    private MutableLiveData<Weather> weatherLiveData;

    private WeatherRepo weatherRepo;

    public WeatherViewModel() {
        weatherLiveData = new MutableLiveData<>();
        weatherRepo = new WeatherRepo(new WeatherDataSource(this));
    }

    public void queryWeather(String cityName) {
        weatherRepo.queryWeather(cityName).observe(lifecycleOwner, new Observer<Weather>() {
            @Override
            public void onChanged(@Nullable Weather weather) {
                weatherLiveData.setValue(weather);
            }
        });
    }

    public MutableLiveData<Weather> getWeatherLiveData() {
        return weatherLiveData;
    }
}

在 QueryWeatherActivity 中打印出接口的请求结果

public class QueryWeatherActivity extends BaseActivity {

    private static final String TAG = "QueryWeatherActivity";

    private WeatherViewModel weatherViewModel;

    private EditText et_cityName;

    private TextView tv_weather;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_query_weather);
        et_cityName = findViewById(R.id.et_cityName);
        tv_weather = findViewById(R.id.tv_weather);
    }

    @Override
    protected ViewModel initViewModel() {
        weatherViewModel = LViewModelProviders.of(this, WeatherViewModel.class);
        weatherViewModel.getWeatherLiveData().observe(this, this::handlerWeather);
        return weatherViewModel;
    }

    private void handlerWeather(Weather weather) {
        StringBuilder result = new StringBuilder();
        for (Weather.InnerWeather.NearestWeather nearestWeather : weather.getData().getWeather()) {
            result.append("\n\n").append(new Gson().toJson(nearestWeather));
        }
        tv_weather.setText(result.toString());
    }

    public void queryWeather(View view) {
        tv_weather.setText(null);
        weatherViewModel.queryWeather(et_cityName.getText().toString());
    }

}

也许有人会觉得为了请求一个接口需要建立三个实现类（WeatherDataSource、WeatherRepo、WeatherViewModel）以及一个接口（IQrCodeDataSource）有点繁琐，但这是想要划分职责并实现逻辑与UI相隔离的必然结果。WeatherDataSource 用来实现接口的实际调用，只负责请求数据并传递请求结果。WeatherRepo 用来屏蔽 WeatherViewModel 对 WeatherDataSource 的感知，并承担起一部分数据处理逻辑。WeatherViewModel 用于实现逻辑与 UI 的隔离，并保障数据不因为页面重建而丢失。这样，Activity 就可以尽量只承担数据呈现的职责，而不必掺杂数据处理逻辑

六、实践操作（2）-请求生成二维码

此处再来看一个例子，用于生成指定内容的二维码

public class QrCodeDataSource extends BaseRemoteDataSource implements IQrCodeDataSource {

    public QrCodeDataSource(BaseViewModel baseViewModel) {
        super(baseViewModel);
    }

    @Override
    public void createQrCode(String text, int width, RequestCallback<QrCode> callback) {
        execute(getService(ApiService.class, HttpConfig.BASE_URL_QR_CODE).createQrCode(text, width), callback);
    }

}

此处接口请求回来的只是一段 base64 编码的字符串，而外部希望获取到的自然是一个可以直接使用的 Bitmap ，因此可以在 Repo 中先对数据进行转换后再传递到外部

public class QrCodeRepo extends BaseRepo<IQrCodeDataSource> {

    public QrCodeRepo(IQrCodeDataSource remoteDataSource) {
        super(remoteDataSource);
    }

    public MutableLiveData<QrCode> createQrCode(String text, int width) {
        MutableLiveData<QrCode> liveData = new MutableLiveData<>();
        remoteDataSource.createQrCode(text, width, new RequestCallback<QrCode>() {
            @SuppressLint("CheckResult")
            @Override
            public void onSuccess(QrCode qrCode) {
                Observable.create(new ObservableOnSubscribe<Bitmap>() {
                    @Override
                    public void subscribe(@NonNull ObservableEmitter<Bitmap> emitter) throws Exception {
                        Bitmap bitmap = base64ToBitmap(qrCode.getBase64_image());
                        emitter.onNext(bitmap);
                        emitter.onComplete();
                    }
                }).subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe(new Consumer<Bitmap>() {
                            @Override
                            public void accept(@NonNull Bitmap bitmap) throws Exception {
                                qrCode.setBitmap(bitmap);
                                liveData.setValue(qrCode);
                            }
                        });
            }
        });
        return liveData;
    }

    private static Bitmap base64ToBitmap(String base64String) {
        byte[] decode = Base64.decode(base64String, Base64.DEFAULT);
        return BitmapFactory.decodeByteArray(decode, 0, decode.length);
    }

}

public class QrCodeViewModel extends BaseViewModel {

    private MutableLiveData<QrCode> qrCodeLiveData;

    private QrCodeRepo qrCodeRepo;

    public QrCodeViewModel() {
        qrCodeLiveData = new MutableLiveData<>();
        qrCodeRepo = new QrCodeRepo(new QrCodeDataSource(this));
    }

    public void createQrCode(String text, int width) {
        qrCodeRepo.createQrCode(text, width).observe(lifecycleOwner, new Observer<QrCode>() {
            @Override
            public void onChanged(@Nullable QrCode qrCode) {
                qrCodeLiveData.setValue(qrCode);
            }
        });
    }

    public MutableLiveData<QrCode> getQrCodeLiveData() {
        return qrCodeLiveData;
    }

}

七、实践操作（3）-请求失败示例

前言说了，本文封装的网络框架当网络请求结果为非成功状态时（网络请求失败或者业务请求失败），默认操作是用 Toast 提示失败原因，也支持自定义实现失败时的操作。此处就来看当请求失败时如何进行处理

此处需要声明两个并不存在的接口

public interface ApiService {

    @GET("leavesC/test1")
    Observable<BaseResponseBody<String>> test1();

    @GET("leavesC/test2")
    Observable<BaseResponseBody<String>> test2();

}

public class FailExampleDataSource extends BaseRemoteDataSource implements IFailExampleDataSource {

    public FailExampleDataSource(BaseViewModel baseViewModel) {
        super(baseViewModel);
    }

    @Override
    public void test1(RequestCallback<String> callback) {
        execute(getService(ApiService.class).test1(), callback);
    }

    @Override
    public void test2(RequestCallback<String> callback) {
        execute(getService(ApiService.class).test2(), callback);
    }

}

public class FailExampleRepo extends BaseRepo<IFailExampleDataSource> {

    public FailExampleRepo(IFailExampleDataSource remoteDataSource) {
        super(remoteDataSource);
    }

    public MutableLiveData<String> test1() {
        MutableLiveData<String> newsPackMutableLiveData = new MutableLiveData<>();
        remoteDataSource.test1(new RequestCallback<String>() {
            @Override
            public void onSuccess(String newsPack) {
                newsPackMutableLiveData.setValue(newsPack);
            }
        });
        return newsPackMutableLiveData;
    }

    public void test2(RequestMultiplyCallback<String> callback) {
        remoteDataSource.test2(callback);
    }

}

test1() 方法用的是基础类的默认失败回调，即直接 Toast 提示失败信息。而 test2() 方法则是自定义了请求失败时的回调操作

public class FailExampleViewModel extends BaseViewModel {

    private MutableLiveData<String> test1LiveData = new MutableLiveData<>();

    private MutableLiveData<String> test2LiveData = new MutableLiveData<>();

    private FailExampleRepo failExampleRepo = new FailExampleRepo(new FailExampleDataSource(this));

    public void test1() {
        failExampleRepo.test1().observe(lifecycleOwner, new Observer<String>() {
            @Override
            public void onChanged(@Nullable String s) {
                test1LiveData.setValue(s);
            }
        });
    }

    public void test2() {
        failExampleRepo.test2(new RequestMultiplyCallback<String>() {
            @Override
            public void onFail(BaseException e) {
                showToast("test2方法请求失败：" + e.getMessage());
                finish();
            }

            @Override
            public void onSuccess(String s) {
                test2LiveData.setValue(s);
            }
        });
    }

}