MVP模式在Android项目中的使用

时间：2021-03-17 21:44:28

　　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。

MVP模式在Android项目中的使用

　　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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