搜了好多相关文章，但是发现貌似都是基于官方Demo中的例子实现的。于是照猫画虎实现了Java版本。

其实其中的核心就是自定义CallAdapter来实现对请求结果的基础处理以及转换。

下面开始正文：

正文

• 引入Retrofit

dependencies {
   ...

    //retrofit
    api 'com.squareup.retrofit2:retrofit:2.8.1'
    api 'com.squareup.okhttp3:okhttp:4.5.0'
    api 'com.squareup.retrofit2:converter-gson:2.5.0'
    api 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'
}

• 自定义一个请求结果的泛型ApiResponse

public class ApiResponse<T> {

    public static final int CODE_SUCCESS = 0;
    public static final int CODE_ERROR = 1;

    public int code; //状态码
    public String msg; //信息
    public T data; //数据

    public ApiResponse(int code, String msg) {
        this.code = code;
        this.msg = msg;
        this.data = null;
    }

    public ApiResponse(int code, String msg, T data) {
        this.code = code;
        this.msg = msg;
        this.data = data;
    }
}

• 自定义 LiveDataCallAdapter

public class LiveDataCallAdapter<T> implements CallAdapter<T, LiveData<T>> {

    private Type mResponseType;
    private boolean isApiResponse;

    LiveDataCallAdapter(Type mResponseType, boolean isApiResponse) {
        this.mResponseType = mResponseType;
        this.isApiResponse = isApiResponse;
    }

    @NotNull
    @Override
    public Type responseType() {
        return mResponseType;
    }

    @NotNull
    @Override
    public LiveData<T> adapt(@NotNull final Call<T> call) {
        return new MyLiveData<>(call, isApiResponse);
    }

    private static class MyLiveData<T> extends LiveData<T> {

        private AtomicBoolean stared = new AtomicBoolean(false);
        private final Call<T> call;
        private boolean isApiResponse;

        MyLiveData(Call<T> call, boolean isApiResponse) {
            this.call = call;
            this.isApiResponse = isApiResponse;
        }

        @Override
        protected void onActive() {
            super.onActive();
            //确保执行一次
            if (stared.compareAndSet(false, true)) {
                call.enqueue(new Callback<T>() {
                    @Override
                    public void onResponse(@NotNull Call<T> call, @NotNull Response<T> response) {
                        T body = response.body();
                        postValue(body);
                    }

                    @Override
                    public void onFailure(@NotNull Call<T> call, @NotNull Throwable t) {
                        if (isApiResponse) {
                            //noinspection unchecked
                            postValue((T) new ApiResponse<>(ApiResponse.CODE_ERROR, t.getMessage()));
                        } else {
                            postValue(null);
                        }
                    }
                });
            }
        }
    }
}

• 自定义 LiveDataCallAdapterFactory

public class LiveDataCallAdapterFactory extends CallAdapter.Factory {

    private static final String TAG = LiveDataCallAdapterFactory.class.getSimpleName();

    @SuppressWarnings("ClassGetClass")
    @Nullable
    @Override
    public CallAdapter<?, ?> get(@NotNull Type returnType, @NotNull Annotation[] annotations, @NotNull Retrofit retrofit) {
        if (getRawType(returnType) != LiveData.class) {
            return null;
        }
        //获取第一个泛型类型
        Type observableType = getParameterUpperBound(0, (ParameterizedType) returnType);
        Class<?> rawType = getRawType(observableType);
        Log.d(TAG, "rawType = " + rawType.getClass().getSimpleName());
        boolean isApiResponse = true;
        if (rawType != ApiResponse.class) {
            //不是返回ApiResponse类型的返回值
            isApiResponse = false;
        }
        if (observableType instanceof ParameterizedType) {
            throw new IllegalArgumentException("resource must be parameterized");
        }
        return new LiveDataCallAdapter<>(observableType, isApiResponse);
    }
}

两个核心类就完成了。

• 自定义Retrofit管理类RetrofitManager

public class RetrofitManager {

    //服务器请求baseUrl
    private static String sBaseUrl = null;

    //超时时长 默认10s
    private static int sConnectTimeout = 10;

    //用于存储retrofit
    private static ConcurrentHashMap<String, Retrofit> sRetrofitMap;

    private static OkHttpClient.Builder sOkHttpBuilder;

    //用于日期转换
    private static Gson sDataFormat;

    static {
        sRetrofitMap = new ConcurrentHashMap<>();

        sOkHttpBuilder = new OkHttpClient.Builder();
        //超时时长
        sOkHttpBuilder.connectTimeout(sConnectTimeout, TimeUnit.SECONDS);

        sDataFormat = new GsonBuilder().setDateFormat("yyyy-MM-dd HH:mm:ss")
                .create();
    }

    //初始化主要的baseUrl  便于后期直接获取
    public static void init(String baseUrl) {
        sBaseUrl = baseUrl;
    }

    public static String getsBaseUrl() {
        return sBaseUrl;
    }

    public static void setConnectTimeout(int connectTimeout) {
        sConnectTimeout = connectTimeout;
    }

    public static Retrofit get() {
        Retrofit retrofit = sRetrofitMap.get(sBaseUrl);
        if (retrofit == null) {
            throw new RuntimeException("BASE_URL为空");
        }
        return retrofit;
    }

    public static Retrofit get(String baseUrl) {
        Retrofit retrofit = sRetrofitMap.get(baseUrl);
        if (retrofit == null) {
            retrofit = createRetrofit(baseUrl);
            sRetrofitMap.put(baseUrl, retrofit);
        }
        return retrofit;
    }

    /**
     * 创建Retrofit对象
     *
     * @param baseUrl baseUrl
     * @return Retrofit
     */
    private static Retrofit createRetrofit(String baseUrl) {
        return new Retrofit.Builder()
                .baseUrl(baseUrl)
                .client(sOkHttpBuilder.build())
                .addCallAdapterFactory(new LiveDataCallAdapterFactory())
                .addConverterFactory(GsonConverterFactory.create(sDataFormat))
                .build();
    }
}

• 最后再定义一个结果类和Service，这里以请求Bing的每日一图为例

public class BingImg {

    //bing每日一图：https://cn.bing.com/HPImageArchive.aspx?format=js&idx=0&n=1
    public static final String REQUEST_URL = "https://cn.bing.com/";

    private static final String BASE_IMAGE_URL = "https://www.bing.com/";

    /**
     * images : [{"startdate":"20200413","fullstartdate":"202004131600","enddate":"20200414","url":"/th?id=OHR.BWFlipper_ZH-CN1813139386_1920x1080.jpg&rf=LaDigue_1920x1080.jpg&pid=hp","urlbase":"/th?id=OHR.BWFlipper_ZH-CN1813139386","copyright":"伊斯塔帕海岸的热带斑海豚，墨西哥 (© Christian Vizl/Tandem Stills + Motion)","copyrightlink":"https://www.bing.com/search?q=%E7%83%AD%E5%B8%A6%E6%96%91%E6%B5%B7%E8%B1%9A&form=hpcapt&mkt=zh-cn","title":"","quiz":"/search?q=Bing+homepage+quiz&filters=WQOskey:%22HPQuiz_20200413_BWFlipper%22&FORM=HPQUIZ","wp":true,"hsh":"b8381f6da75ae67b3581c0ca162718ac","drk":1,"top":1,"bot":1,"hs":[]}]
     * tooltips : {"loading":"正在加载...","previous":"上一个图像","next":"下一个图像","walle":"此图片不能下载用作壁纸。","walls":"下载今日美图。仅限用作桌面壁纸。"}
     */

    public TooltipsBean tooltips;
    public List<ImagesBean> images;

    public static class TooltipsBean {
        /**
         * loading : 正在加载...
         * previous : 上一个图像
         * next : 下一个图像
         * walle : 此图片不能下载用作壁纸。
         * walls : 下载今日美图。仅限用作桌面壁纸。
         */

        public String loading;
        public String previous;
        public String next;
        public String walle;
        public String walls;
    }

    public static class ImagesBean {
        /**
         * startdate : 20200413
         * fullstartdate : 202004131600
         * enddate : 20200414
         * url : /th?id=OHR.BWFlipper_ZH-CN1813139386_1920x1080.jpg&rf=LaDigue_1920x1080.jpg&pid=hp
         * urlbase : /th?id=OHR.BWFlipper_ZH-CN1813139386
         * copyright : 伊斯塔帕海岸的热带斑海豚，墨西哥 (© Christian Vizl/Tandem Stills + Motion)
         * copyrightlink : https://www.bing.com/search?q=%E7%83%AD%E5%B8%A6%E6%96%91%E6%B5%B7%E8%B1%9A&form=hpcapt&mkt=zh-cn
         * title :
         * quiz : /search?q=Bing+homepage+quiz&filters=WQOskey:%22HPQuiz_20200413_BWFlipper%22&FORM=HPQUIZ
         * wp : true
         * hsh : b8381f6da75ae67b3581c0ca162718ac
         * drk : 1
         * top : 1
         * bot : 1
         * hs : []
         */

        public String startdate;
        public String fullstartdate;
        public String enddate;
        public String url;
        public String urlbase;
        public String copyright;
        public String copyrightlink;
        public String title;
        public String quiz;
        public boolean wp;
        public String hsh;
        public int drk;
        public int top;
        public int bot;
        public List<?> hs;
    }

    /**
     * 获取每日一图的url
     *
     * @return url
     */
    public String getImgUrl() {
        if (images != null && images.size() >= 1) {
            return BASE_IMAGE_URL + images.get(0).url;
        }
        return null;
    }
}

public interface SplashService {

    @GET("HPImageArchive.aspx?format=js&idx=0&n=1")
    Call<BingImg> getBingImg();

    @GET("HPImageArchive.aspx?format=js&idx=0&n=1")
    LiveData<BingImg> getBingImgLiveData();
}

使用

RetrofitManager.get("https://cn.bing.com/")
        .create(SplashService.class)
        .getBingImgLiveData().observe(this, new Observer<BingImg>() {
    @Override
    public void onChanged(BingImg bingImg) {
        Log.d(TAG, "onChanged: 请求结果："+new Gson().toJson(bingImg));
    }
});

Demo链接

参考文章

• GithubBrowserSample
• LiveData+Retrofit网络请求实战
• Retrofit与LiveData结合