【Android高级工程师见解】MVP模式在Android项目中
2020-10-09 本文已影响0人
jett老师
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
