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[操作系统]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:

<??><android.support.v4.widget.SwipeRefreshLayout  ="http://schemas.android.com/apk/res/android"  ="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