1. 介绍

最近基于 Wanandroid开放API 开发了一款十分简单的APP，, 采用 Androidx + MVVM + Retrofit + dataBinding 的模式进行开发。App的主要功能是就是浏览各类 Android 文章，效果图如下所示：

1.1 功能效果图展示

主页	项目	微信公众号	知识体系

文章详情	我的	注册	导航

1.2 项目设计模式

该项目采用 MVVM 的开发模式，关于 MVVM 开发模式，可以参考：美团如何构建Android MVVM 应用框架，如果你觉得不易理解，可以参考一下 Android MVC MVP MVVM简单例子

MVVM 的经典架构图： MVVM的经典架构图项目中的架构图为：项目架构图

2. 代码解析

举个例子：比如我们的主页，有 banner广告图以及首页文章，如下所示：

所以要实现这样的功能，我们需要为 HomeFragment 创建 HomeViewModel、HomeRepository、HomeBeanFiles，如下所示：

具体代码见：Wanandroid_Learning

HomeFragment.java

public class HomeFragment extends Fragment {
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        //创建 ViewModel
        HomeViewModel homeVm = ViewModelProviders.of(this, new ViewModelFactory()).get(HomeViewModel.class);
        //观察 banner data
        homeVm.getHomeBannerListLd().observe(getViewLifecycleOwner(), bannerListDataObserver);
        homeVm.setHomeBannerListLd();
        //观察 Article data
        homeVm.getHomeArticleListBeanLd().observe(getViewLifecycleOwner(), articleListBeanObserver);
        homeVm.setHomeArticleListBeanLd();
    }

    ···略···
}

HomeViewModel.java

public class HomeViewModel extends ViewModel {
    private static final String TAG = "HomeViewModel";
    private MutableLiveData<HomeBannerListBean> homeBannerListLd;
    private MutableLiveData<HomeArticleListBean> homeArticleListBeanLd;

    public HomeViewModel() {
        this.homeBannerListLd = new MutableLiveData<>();
        this.homeArticleListBeanLd = new MutableLiveData<>();
    }

    public MutableLiveData<HomeBannerListBean> getHomeBannerListLd() {
        return homeBannerListLd;
    }

    public void setHomeBannerListLd() {
        HomeRepository.newInstance().getHomeBannerList(new GetWebDataListener() {
            @Override
            public void getDataSuccess(Object object) {
                HomeBannerListBean homeBannerListBean = (HomeBannerListBean) object;
                homeBannerListLd.postValue(homeBannerListBean);
            }

            @Override
            public void getDataFailed(String failedMsg) {
                Log.e(TAG, "getDataFailed: " + failedMsg);
            }
        });
    }

    public MutableLiveData<HomeArticleListBean> getHomeArticleListBeanLd() {
        return homeArticleListBeanLd;
    }

    public void setHomeArticleListBeanLd() {
        HomeRepository.newInstance().getHomeArticleList(0, new GetWebDataListener() {
            @Override
            public void getDataSuccess(Object object) {
                HomeArticleListBean homeArticleListBean = (HomeArticleListBean) object;
                homeArticleListBeanLd.postValue(homeArticleListBean);
            }

            @Override
            public void getDataFailed(String failedMsg) {
                Log.e(TAG, "getDataFailed: " + failedMsg);
            }
        });
    }
}

HomeRepository.java

public class HomeRepository {
    /**
     * 为了防止出现DCL失效问题，所以用 volatile 关键字来修饰 instance。
     */
    private volatile static HomeRepository instance;

    public static HomeRepository newInstance() {
        if (instance == null) {
            synchronized (HomeRepository.class) {
                if (instance == null) {
                    instance = new HomeRepository();
                }
            }
        }
        return instance;
    }

    public void getHomeBannerList(final GetWebDataListener listener) {
        ApiService apiService = ApiWrapper.getRetrofitInstance().create(ApiService.class);
        apiService.getHomeBannerList().enqueue(new AbstractRetrofitCallback() {
            @Override
            public void getSuccessful(String responseBody) {
                Gson gson = new Gson();
                HomeBannerListBean homeBannerListBean = gson.fromJson(responseBody, HomeBannerListBean.class);
                listener.getDataSuccess(homeBannerListBean);
            }

            @Override
            public void getFailed(String failedMsg) {
                listener.getDataFailed(failedMsg);
            }
        });
    }

    public void getHomeArticleList(int pageNumber, final GetWebDataListener listener) {
        ApiService apiService = ApiWrapper.getRetrofitInstance().create(ApiService.class);
        apiService.getHomeArticleList(pageNumber).enqueue(new AbstractRetrofitCallback() {
            @Override
            public void getSuccessful(String responseBody) {
                Gson gson = new Gson();
                HomeArticleListBean homeArticleListBean = gson.fromJson(responseBody, HomeArticleListBean.class);
                listener.getDataSuccess(homeArticleListBean);
            }

            @Override
            public void getFailed(String failedMsg) {
                listener.getDataFailed(failedMsg);
            }
        });
    }

}