• 前言

• 实践

• 前言
  MVP（Model View Presenter）模式是MVC模式的一个演化版本，目前在Android应用开发中越来越重要。随着UI创建技术的功能日益增强，UI层也履行越来越多的职责。为了更好地细分视图（View）和模型（Model）的功能，让View专注于处理数据的可视化以及与用户的交互，同时让Model只关系数据的处理，基于MVC概念的MVP模式应运而生。

那什么是MVP模式呢？

MVP模式通常包含4个要素:
1.View：负责绘制UI元素，与用户进行交互（Android中体现为Activity/Fragment等）
2.View Interface：需要View实现的接口，View通过View Interface与Presenter进行交互，降低耦合，方便单元测试
3.Model：负责存储、检索、操作数据（有时实现一个Model Interface降低耦合）
4.Presenter：作为View与Model交互的中间纽带，处理与用户交互的逻辑

那么为什么在移动开发中推荐使用MVP呢？与MVC的差异在哪？

MVP是从MVC演变而来，它们的基本思想有想通的地方：Controller/Presenter负责逻辑的处理，Model提供数据，View负责显示。重大区别是在MVP中View并不直接使用Model，它们的通信是通过Presenter（MVC中的Controller）来进行的，所有的交互都发生在Presenter内部，而在MVC中View会直接从Model中读取数据。

我们在学习阶段写的逻辑一般都是在Activity中完成的，这样随着项目需求越来越多，Activity中代码越来越复杂，重构难度不断加大。同时也给测试提供了方便。

//新闻实体类
package com.lauren.simplenews.beans;
import java.io.Serializable;
public class NewsBean implements Serializable {
    /**     * docid     */
    private String docid;
    /**     * 标题     */
    private String title;
    /**     * 小内容     */
    private String digest;
    /**     * 图片地址     */
    private String imgsrc;
    /**     * 来源     */
    private String source;
    /**     * 时间     */
    private String ptime;
    /**     * TAG     */
    private String tag;
    public String getDocid() {        return docid;     }
    public void setDocid(String docid) {        this.docid = docid;    }
    public String getTitle() {        return title;    }
    public void setTitle(String title) {        this.title = title;    }
    public String getDigest() {        return digest;    }
    public void setDigest(String digest) {        this.digest = digest;    }
    public String getImgsrc() {        return imgsrc;    }
    public void setImgsrc(String imgsrc) {        this.imgsrc = imgsrc;    }
    public String getSource() {        return source;    }
    public void setSource(String source) {        this.source = source;    }
    public String getPtime() {        return ptime;    }
    public void setPtime(String ptime) {        this.ptime = ptime;    }
    public String getTag() {        return tag;    }
    public void setTag(String tag) {        this.tag = tag;    }
}

//Model Interface
public interface NewsModel {
    void loadNews(String url, int type, NewsModelImpl.OnLoadNewsListListener listener);
    void loadNewsDetail(String docid, NewsModelImpl.OnLoadNewsDetailListener listener);
}

//Model Impl
public class NewsModelImpl implements NewsModel {
    @Override
    public void loadNews(String url, final int type, final OnLoadNewsListListener listener) {
        OkHttpUtils.ResultCallback<String> loadNewsCallback = new OkHttpUtils.ResultCallback<String>() {
            @Override
            public void onSuccess(String response) {
                List<NewsBean> newsBeanList = NewsJsonUtils.readJsonNewsBeans(response, getID(type));
                listener.onSuccess(newsBeanList);
            }
            @Override
            public void onFailure(Exception e) {
                listener.onFailure("load news list failure.", e);
            }
        };
        OkHttpUtils.get(url, loadNewsCallback);
    } 
   @Override
    public void loadNewsDetail(final String docid, final OnLoadNewsDetailListener listener) {
        String url = getDetailUrl(docid);
        OkHttpUtils.ResultCallback<String> loadNewsCallback = new OkHttpUtils.ResultCallback<String>() {
            @Override
            public void onSuccess(String response) {
                NewsDetailBean newsDetailBean = NewsJsonUtils.readJsonNewsDetailBeans(response, docid);
                listener.onSuccess(newsDetailBean);
            } 
           @Override
            public void onFailure(Exception e) {
                listener.onFailure("load news detail info failure.", e);
            }
        };
        OkHttpUtils.get(url, loadNewsCallback);
    }
    private String getID(int type) {
        String id;
        switch (type) {
            case NewsFragment.NEWS_TYPE_TOP:
                id = Urls.TOP_ID;
                break;
            case NewsFragment.NEWS_TYPE_NBA:
                id = Urls.NBA_ID;
                break;
            case NewsFragment.NEWS_TYPE_CARS:
                id = Urls.CAR_ID;
                break;
            case NewsFragment.NEWS_TYPE_JOKES:
                id = Urls.JOKE_ID;
                break;
            default:
                id = Urls.TOP_ID;
                break;
        }
        return id;
    }
    private String getDetailUrl(String docId) {
        StringBuffer sb = new StringBuffer(Urls.NEW_DETAIL);
        sb.append(docId).append(Urls.END_DETAIL_URL);
        return sb.toString();
    }
    public interface OnLoadNewsListListener {
        void onSuccess(List<NewsBean> list);
        void onFailure(String msg, Exception e);
    }
    public interface OnLoadNewsDetailListener {
        void onSuccess(NewsDetailBean newsDetailBean);
        void onFailure(String msg, Exception e);
    }
}

//View Interface
public interface NewsView {
    void showProgress();
    void addNews(List<NewsBean> newsList);
    void hideProgress();
    void showLoadFailMsg();
}
//View
public class NewsListFragment extends Fragment implements NewsView,
 SwipeRefreshLayout.OnRefreshListener {
    private static final String TAG = "NewsListFragment";
    private SwipeRefreshLayout mSwipeRefreshWidget;
    private RecyclerView mRecyclerView;
    private LinearLayoutManager mLayoutManager;
    private NewsAdapter mAdapter;
    private List<NewsBean> mData;
    private NewsPresenter mNewsPresenter;
    private int mType = NewsFragment.NEWS_TYPE_TOP;
    private int pageIndex = 0;
    public static NewsListFragment newInstance(int type) {
        Bundle args = new Bundle();
        NewsListFragment fragment = new NewsListFragment();
        args.putInt("type", type);
        fragment.setArguments(args);
        return fragment;
    }
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mNewsPresenter = new NewsPresenterImpl(this);
        mType = getArguments().getInt("type");
    }
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle
 savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_newslist, null);
        mSwipeRefreshWidget = (SwipeRefreshLayout) view.findViewById(R.id.swipe_refresh_widget);
        mSwipeRefreshWidget.setColorSchemeResources(R.color.primary,
                R.color.primary_dark, R.color.primary_light,
                R.color.accent);
        mSwipeRefreshWidget.setOnRefreshListener(this);
        mRecyclerView = (RecyclerView)view.findViewById(R.id.recycle_view);
        mRecyclerView.setHasFixedSize(true);
        mLayoutManager = new LinearLayoutManager(getActivity());
        mRecyclerView.setLayoutManager(mLayoutManager);
        mRecyclerView.setItemAnimator(new DefaultItemAnimator());
        mAdapter = new NewsAdapter(getActivity().getApplicationContext()); 
        mAdapter.setOnItemClickListener(mOnItemClickListener);
        mRecyclerView.setAdapter(mAdapter);
        mRecyclerView.addOnScrollListener(mOnScrollListener);
        onRefresh();
        return view;
    }
    private RecyclerView.OnScrollListener mOnScrollListener = new RecyclerView.OnScrollListener() {
        private int lastVisibleItem;
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            lastVisibleItem = mLayoutManager.findLastVisibleItemPosition();
        }
        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            if (newState == RecyclerView.SCROLL_STATE_IDLE 
                   && lastVisibleItem + 1 == mAdapter.getItemCount()
                    && mAdapter.isShowFooter()) {
                //加载更多
                LogUtils.d(TAG, "loading more data");
                mNewsPresenter.loadNews(mType, pageIndex + Urls.PAZE_SIZE);
            }
        }
    };
    private NewsAdapter.OnItemClickListener mOnItemClickListener = new
 NewsAdapter.OnItemClickListener() {
        @Override
        public void onItemClick(View view, int position) {
            NewsBean news = mAdapter.getItem(position);
            Intent intent = new Intent(getActivity(), NewsDetailActivity.class);
            intent.putExtra("news", news);
            View transitionView = view.findViewById(R.id.ivNews); 
            ActivityOptionsCompat options =
                    ActivityOptionsCompat.makeSceneTransitionAnimation(getActivity(), 
                           transitionView, getString(R.string.transition_news_img));
            ActivityCompat.startActivity(getActivity(), intent, options.toBundle());
        }
    };
    @Override    public void showProgress() {
        mSwipeRefreshWidget.setRefreshing(true);
    }
    @Override
    public void addNews(List<NewsBean> newsList) {
        mAdapter.isShowFooter(true);
        if(mData == null) {
            mData = new ArrayList<NewsBean>();
        }
        mData.addAll(newsList);
        if(pageIndex == 0) {
            mAdapter.setmDate(mData);
        } else {
            //如果没有更多数据了,则隐藏footer布局
            if(newsList == null || newsList.size() == 0) {
                mAdapter.isShowFooter(false);
            }
            mAdapter.notifyDataSetChanged();
        }
        pageIndex += Urls.PAZE_SIZE;
    }
    @Override    public void hideProgress() {
        mSwipeRefreshWidget.setRefreshing(false);
    } 
   @Override
    public void showLoadFailMsg() {
        if(pageIndex == 0) {
            mAdapter.isShowFooter(false);
            mAdapter.notifyDataSetChanged();
        }
        View view = getActivity() == null ? mRecyclerView.getRootView() :
 getActivity().findViewById(R.id.drawer_layout);
        Snackbar.make(view, getString(R.string.load_fail), Snackbar.LENGTH_SHORT).show();
    }
    @Override
    public void onRefresh() {
        pageIndex = 0;
        if(mData != null) {
            mData.clear();
        }
        mNewsPresenter.loadNews(mType, pageIndex);
    }
}