【Android高级工程师见解】MVP模式在Android项目中

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