复杂的MVP

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MVP模式在Android项目中的使用

　　以前在写项目的时候，没有过多考虑架构模式的问题，因为之前一直做J2EE开发，而J2EE都是采用MVC模式进行开发的，所以在搭建公司项目的时候，也是使用类似MVC的架构（严格来讲，之前的项目还算不上MVC模式，只是简单将网络请求与界面分离，然后通过Handle通知更新界面）。这种写法，在后面随着项目越来越大，Activty或者Fragment中代码也会越来越多，导致项目的维护变的越来越复杂。所以需要另外一种架构模式来解决这个问题，在网上浏览了一圈，发现适合Android开发的架构模式非MVP莫属了。

　　网上一搜，讲MVP模式的文章比比皆是。但是大多都是讲理论，稍微好点的会附带一个简单的登录的demo。一个简单的demo很难让初次接触MVP模式的人掌握它的使用。所以我决定写一个稍微复杂一点的新闻客户端SimpleNews（当然只是相对登录的demo）来展示MVP在具体项目中的使用。另外SimpleNews还使用了Material Design，也是学习Material Design的一个好Demo。

　　好了，切入正文吧。先讲一下MVP的概念。

什么是MVP

　　MVP是模型（Model）、视图（View）、主持人（Presenter）的缩写，分别代表项目中3个不同的模块。

　　模型（Model）：负责处理数据的加载或者存储，比如从网络或本地数据库获取数据等；

　　视图（View）：负责界面数据的展示，与用户进行交互；

　　主持人（Presenter）：相当于协调者，是模型与视图之间的桥梁，将模型与视图分离开来。

　　如下图所示，View与Model并不直接交互，而是使用Presenter作为View与Model之间的桥梁。其中Presenter中同时持有Viwe层以及Model层的Interface的引用，而View层持有Presenter层Interface的引用。当View层某个界面需要展示某些数据的时候，首先会调用Presenter层的某个接口，然后Presenter层会调用Model层请求数据，当Model层数据加载成功之后会调用Presenter层的回调方法通知Presenter层数据加载完毕，最后Presenter层再调用View层的接口将加载后的数据展示给用户。这就是MVP模式的整个核心过程。

　　这样分层的好处就是大大减少了Model与View层之间的耦合度。一方面可以使得View层和Model层单独开发与测试，互不依赖。另一方面Model层可以封装复用，可以极大的减少代码量。当然，MVP还有其他的一些优点，这里不再赘述。下面看下MVP模式在具体项目中的使用。

MVP模式在项目中的使用

1、View层

　　View层新闻展示模块的是组件是Fragment，里面有一个RecyclerView、SwipeRefreshLayout。布局代码如下：

<?xml version="1.0" encoding="utf-8"?><android.support.v4.widget.SwipeRefreshLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    android:id="@+id/swipe_refresh_widget"    android:layout_width="match_parent"    android:layout_height="match_parent">    <android.support.v7.widget.RecyclerView        android:id="@+id/recycle_view"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:scrollbars="vertical"        app:layout_behavior="@string/appbar_scrolling_view_behavior"        android:paddingTop="@dimen/card_margin">    </android.support.v7.widget.RecyclerView></android.support.v4.widget.SwipeRefreshLayout>

　　新闻列表模块主要是展示从网络获取的新闻列表信息，View层的接口大概需要如下方法：

　　（1）加载数据的过程中需要提示“正在加载”的反馈信息给用户

　　（2）加载成功后，将加载得到的数据填充到RecyclerView展示给用户

　　（3）加载成功后，需要将“正在加载”反馈信息取消掉

　　（4）若加载数据失败，如无网络连接，则需要给用户提示信息

　　根据上面描述，我们将View层的接口定义如下，分别对应上面四个方法：

public interface NewsView {    void showProgress();    void addNews(List<NewsBean> newsList);    void hideProgress();    void showLoadFailMsg();}

　　在新闻列表Fragment中实现上述接口：

package com.lauren.simplenews.news.widget;import android.content.Intent;import android.os.Bundle;import android.support.annotation.Nullable;import android.support.design.widget.Snackbar;import android.support.v4.app.ActivityCompat;import android.support.v4.app.ActivityOptionsCompat;import android.support.v4.app.Fragment;import android.support.v4.widget.SwipeRefreshLayout;import android.support.v7.widget.DefaultItemAnimator;import android.support.v7.widget.LinearLayoutManager;import android.support.v7.widget.RecyclerView;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import com.lauren.simplenews.R;import com.lauren.simplenews.beans.NewsBean;import com.lauren.simplenews.commons.Urls;import com.lauren.simplenews.news.NewsAdapter;import com.lauren.simplenews.news.presenter.NewsPresenter;import com.lauren.simplenews.news.presenter.NewsPresenterImpl;import com.lauren.simplenews.news.view.NewsView;import com.lauren.simplenews.utils.LogUtils;import java.util.ArrayList;import java.util.List;/** * Description : 新闻Fragment * Author : lauren * Email  : lauren.liuling@gmail.com * Blog   : http://www.liuling123.com * Date   : 15/12/13 */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.setOnScrollListener(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();        }        Snackbar.make(getActivity().findViewById(R.id.drawer_layout), getString(R.string.load_fail), Snackbar.LENGTH_SHORT).show();    }    @Override    public void onRefresh() {        pageIndex = 0;        if(mData != null) {            mData.clear();        }        mNewsPresenter.loadNews(mType, pageIndex);    }}

2、Model层

　　新闻模块的model主要负责从服务器获取新闻列表信息，接口代码如下：

public interface NewsModel {    void loadNews(String url, int type, NewsModelImpl.OnLoadNewsListListener listener);    ......}

　　实现如下：

package com.lauren.simplenews.news.model;import com.lauren.simplenews.beans.NewsBean;import com.lauren.simplenews.beans.NewsDetailBean;import com.lauren.simplenews.commons.Urls;import com.lauren.simplenews.news.NewsJsonUtils;import com.lauren.simplenews.news.widget.NewsFragment;import com.lauren.simplenews.utils.OkHttpUtils;import java.util.List;/** * Description : 新闻业务处理类 * Author : lauren * Email  : lauren.liuling@gmail.com * Blog   : http://www.liuling123.com * Date   : 15/12/19 */public class NewsModelImpl implements NewsModel {    /**     * 加载新闻列表     * @param url     * @param listener     */    @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);    }    ......    /**     * 获取ID     * @param type     * @return     */    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);    }    ......}

　　网络请求使用开源项目OkHttp，OkHttpUtils是对其的封装，具体代码如下：

package com.lauren.simplenews.utils;import android.os.Handler;import android.os.Looper;import com.google.gson.internal.$Gson$Types;import com.squareup.okhttp.Callback;import com.squareup.okhttp.FormEncodingBuilder;import com.squareup.okhttp.OkHttpClient;import com.squareup.okhttp.Request;import com.squareup.okhttp.RequestBody;import com.squareup.okhttp.Response;import java.io.IOException;import java.lang.reflect.ParameterizedType;import java.lang.reflect.Type;import java.net.CookieManager;import java.net.CookiePolicy;import java.util.List;import java.util.concurrent.TimeUnit;/** * Description : OkHttp网络连接封装工具类 * Author : lauren * Email  : lauren.liuling@gmail.com * Blog   : http://www.liuling123.com * Date   : 15/12/17 */public class OkHttpUtils {    private static final String TAG = "OkHttpUtils";    private static OkHttpUtils mInstance;    private OkHttpClient mOkHttpClient;    private Handler mDelivery;    private OkHttpUtils() {        mOkHttpClient = new OkHttpClient();        mOkHttpClient.setConnectTimeout(10, TimeUnit.SECONDS);        mOkHttpClient.setWriteTimeout(10, TimeUnit.SECONDS);        mOkHttpClient.setReadTimeout(30, TimeUnit.SECONDS);        //cookie enabled        mOkHttpClient.setCookieHandler(new CookieManager(null, CookiePolicy.ACCEPT_ORIGINAL_SERVER));        mDelivery = new Handler(Looper.getMainLooper());    }    private synchronized static OkHttpUtils getmInstance() {        if (mInstance == null) {            mInstance = new OkHttpUtils();        }        return mInstance;    }    private void getRequest(String url, final ResultCallback callback) {        final Request request = new Request.Builder().url(url).build();        deliveryResult(callback, request);    }    private void postRequest(String url, final ResultCallback callback, List<Param> params) {        Request request = buildPostRequest(url, params);        deliveryResult(callback, request);    }    private void deliveryResult(final ResultCallback callback, Request request) {        mOkHttpClient.newCall(request).enqueue(new Callback() {            @Override            public void onFailure(Request request, final IOException e) {                sendFailCallback(callback, e);            }            @Override            public void onResponse(Response response) throws IOException {                try {                    String str = response.body().string();                    if (callback.mType == String.class) {                        sendSuccessCallBack(callback, str);                    } else {                        Object object = JsonUtils.deserialize(str, callback.mType);                        sendSuccessCallBack(callback, object);                    }                } catch (final Exception e) {                    LogUtils.e(TAG, "convert json failure", e);                    sendFailCallback(callback, e);                }            }        });    }    private void sendFailCallback(final ResultCallback callback, final Exception e) {        mDelivery.post(new Runnable() {            @Override            public void run() {                if (callback != null) {                    callback.onFailure(e);                }            }        });    }    private void sendSuccessCallBack(final ResultCallback callback, final Object obj) {        mDelivery.post(new Runnable() {            @Override            public void run() {                if (callback != null) {                    callback.onSuccess(obj);                }            }        });    }    private Request buildPostRequest(String url, List<Param> params) {        FormEncodingBuilder builder = new FormEncodingBuilder();        for (Param param : params) {            builder.add(param.key, param.value);        }        RequestBody requestBody = builder.build();        return new Request.Builder().url(url).post(requestBody).build();    }    /**********************对外接口************************/    /**     * get请求     * @param url  请求url     * @param callback  请求回调     */    public static void get(String url, ResultCallback callback) {        getmInstance().getRequest(url, callback);    }    /**     * post请求     * @param url       请求url     * @param callback  请求回调     * @param params    请求参数     */    public static void post(String url, final ResultCallback callback, List<Param> params) {        getmInstance().postRequest(url, callback, params);    }    /**     * http请求回调类,回调方法在UI线程中执行     * @param <T>     */    public static abstract class ResultCallback<T> {        Type mType;        public ResultCallback(){            mType = getSuperclassTypeParameter(getClass());        }        static Type getSuperclassTypeParameter(Class<?> subclass) {            Type superclass = subclass.getGenericSuperclass();            if (superclass instanceof Class) {                throw new RuntimeException("Missing type parameter.");            }            ParameterizedType parameterized = (ParameterizedType) superclass;            return $Gson$Types.canonicalize(parameterized.getActualTypeArguments()[0]);        }        /**         * 请求成功回调         * @param response         */        public abstract void onSuccess(T response);        /**         * 请求失败回调         * @param e         */        public abstract void onFailure(Exception e);    }    /**     * post请求参数类     */    public static class Param {        String key;        String value;        public Param() {        }        public Param(String key, String value) {            this.key = key;            this.value = value;        }    }}

　　将网络请求进行封装可以减少很多的代码量，并且后期如果我不想用okhttp了，想换成其它的库，修改起来也方便。

3、Presenter层

　　View层需要调用Presenter层加载新闻信息，所以Presenter需要提供加载新闻信息的接口：

public interface NewsPresenter {    void loadNews(int type, int page);}

　　NewsPresenterImpl的构造函数中需要传入View层的接口对象NewView，并且需要创建一个NewsModel对象。Presenter的具体实现：

package com.lauren.simplenews.news.presenter;import com.lauren.simplenews.beans.NewsBean;import com.lauren.simplenews.commons.Urls;import com.lauren.simplenews.news.model.NewsModel;import com.lauren.simplenews.news.model.NewsModelImpl;import com.lauren.simplenews.news.view.NewsView;import com.lauren.simplenews.news.widget.NewsFragment;import com.lauren.simplenews.utils.LogUtils;import java.util.List;/** * Description : * Author : lauren * Email  : lauren.liuling@gmail.com * Blog   : http://www.liuling123.com * Date   : 15/12/18 */public class NewsPresenterImpl implements NewsPresenter, NewsModelImpl.OnLoadNewsListListener {    private static final String TAG = "NewsPresenterImpl";    private NewsView mNewsView;    private NewsModel mNewsModel;    public NewsPresenterImpl(NewsView newsView) {        this.mNewsView = newsView;        this.mNewsModel = new NewsModelImpl();    }    @Override    public void loadNews(final int type, final int pageIndex) {        String url = getUrl(type, pageIndex);        LogUtils.d(TAG, url);        //只有第一页的或者刷新的时候才显示刷新进度条        if(pageIndex == 0) {            mNewsView.showProgress();        }        mNewsModel.loadNews(url, type, this);    }    /**     * 根据类别和页面索引创建url     * @param type     * @param pageIndex     * @return     */    private String getUrl(int type, int pageIndex) {        StringBuffer sb = new StringBuffer();        switch (type) {            case NewsFragment.NEWS_TYPE_TOP:                sb.append(Urls.TOP_URL).append(Urls.TOP_ID);                break;            case NewsFragment.NEWS_TYPE_NBA:                sb.append(Urls.COMMON_URL).append(Urls.NBA_ID);                break;            case NewsFragment.NEWS_TYPE_CARS:                sb.append(Urls.COMMON_URL).append(Urls.CAR_ID);                break;            case NewsFragment.NEWS_TYPE_JOKES:                sb.append(Urls.COMMON_URL).append(Urls.JOKE_ID);                break;            default:                sb.append(Urls.TOP_URL).append(Urls.TOP_ID);                break;        }        sb.append("/").append(pageIndex).append(Urls.END_URL);        return sb.toString();    }    @Override    public void onSuccess(List<NewsBean> list) {        mNewsView.hideProgress();        mNewsView.addNews(list);    }    @Override    public void onFailure(String msg, Exception e) {        mNewsView.hideProgress();        mNewsView.showLoadFailMsg();    }}

　　当用户切换到NewsListFragment界面之后，界面需要展示新闻列表信息给用户。首先NewsListFragment会调用NewsPresenter的loadNews方法，NewsPresenter 的loadNews方法中又会调用NewsModel中的loadNews方法。NewsModel中的loadNews方法中就是加载数据的核心，通过Okhttp请求服务器接口获取数据，无论数据获取成功与否，都会通过OnLoadNewsListener接口回调给NewsPresenter 。如果获取成功，NewsPresenter 会调用NewsView的addNews方法将获取的新闻列表信息展示到RecyclerView。如果获取失败，则调用NewsView的showLoadFialMsg方法向用户提示失败信息。

　　以上就是新闻列表请求的整个过程。

　　源码地址：https://github.com/liuling07/SimpleNews

　　转载请注明出处：http://www.liuling123.com/2015/12/mvp-pattern-android.html

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