[尝试]给Retrofit请求做一个统一入口

在页面请求数据时，多数情况需要在页面退出时检查请求是否响应完成，如果没有响应或正在请求中，这时就需要将这些请求cancel掉。
比较方便的方式是，在页面基类中统一管理Retrofit Call，在页面onDestroy*的时候批量cancel掉当前页面中发起的所有请求Call。

定义页面请求Flag
public interface Questioner {
    String giveRequestId();
}

/**
  * 创建网络请求
  * @param questioner questioner
  * @param params Request Params
  * @param <T> Result
  * @return Call
  */
public <S,T> Call<T> createRequestCall(Questioner questioner, Class<S> SERVICE, String apiName, String[] params) {
    final String requestId = questioner.giveRequestId();
    final Class[] cPs = new Class[params == null ? 0 : params.length];
    for (int i = 0; i < cPs.length; i++) {
        cPs[i] = String.class;
    }
    try {
        Method method = SERVICE.getDeclaredMethod(apiName, cPs);
        S service = mRetrofit.create(SERVICE);
        Object[] oPs = new Object[params == null ? 0 : params.length];
        if (params != null) System.arraycopy(params, 0, oPs, 0, oPs.length);
        final Call<T> rawCall = (Call<T>) method.invoke(service, oPs);
        synchronized (mRequestSync) {
            List<Call<?>> requests = mRequestMap.get(requestId);
            if (requests == null) requests = new LinkedList<>();
            requests.add(rawCall);
            mRequestMap.put(requestId, requests);
        }
        return rawCall;
    } catch (NoSuchMethodException e) {
        return null;
    } catch (InvocationTargetException | IllegalAccessException e) {
        return null;
    }
}

/**
  * 请求网络数据
  * @param questioner questioner
  * @param params Request Params
  * @param <T> Result
  * @return Call
  */
public <S,T> Call<T> request(Questioner questioner, Class<S> SERVICE, String apiName, String[] params, final DataCallback<T> callback) {
    final Questioner fQuestioner = questioner;
    final Call<T> rawCall = createRequestCall(questioner, SERVICE, apiName, params);
    final Handler uiHandler = new Handler(Looper.getMainLooper());
    uiHandler.post(new Runnable() {
        @Override
        public void run() {
            if (callback != null) {
                callback.onRequest(rawCall);
            }
        }
    });
    if (rawCall != null) {
        rawCall.enqueue(new Callback<T>() {
            @Override
            public void onResponse(final Call<T> call, final Response<T> response) {
                uiHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        if (callback != null) {
                            callback.onResponse(call, response.body());
                        }
                    }
                });
                removeCall(fQuestioner, rawCall);
            }
            @Override
            public void onFailure(final Call<T> call, final Throwable throwable) {
                uiHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        if (callback != null) {
                            callback.onFailure(call, throwable);
                        }
                    }
                });
                removeCall(fQuestioner, rawCall);
            }
        });
    }
    return rawCall;
}

发起请求只需要如下操作

request(DemoApi.class, "test" /*DemoApi中定义的方法名称*/, new String[]{""} /*方法的参数String数组*/, new DataCallback<TestResult>() {
    @Override
    public void onRequest(Call<TestResult> call) {
    }
    @Override
    public void onResponse(Call<TestResult> call, @Nullable TestResult result) {
    }
    @Override
    public void onFailure(Call<TestResult> call, Throwable t) {
    }
});

取消请求 - 这个方法可以在实现了Questioner接口的Activity销毁时统一调用，业务逻辑中只发起请求即可，不必单独取消某个网络请求

/**
  * 取消给定Questioner的所有网络请求
  * @param questioner questioner
  */
public void cancel(Questioner questioner) {
    final String requestId = questioner.giveRequestId();
    synchronized (mRequestSync) {
        List<Call<?>> requests = mRequestMap.get(requestId);
        if (requests != null) {
            for (int i = 0; i < requests.size(); i++) {
                Call<?> call = requests.get(i);
                if (!call.isExecuted() && !call.isCanceled()) {
                    call.cancel();
                }
            }
        }
        mRequestMap.remove(requestId);
    }
}