MVP 模式实现

╰半橙微兮° 2022-05-29 06:52 170阅读 0赞

参考文章：

[ Android MVP 开发模式优缺点][Android MVP]  
该文章是其他博主文章，原文地址:[ 你的MVP模式写法是否及格][_MVP]

一般我们做项目都会选择使用MVP进行解耦，关于MVP大家早都耳熟能详了，由于之前接手的项目中使用的MVP模式写法相当随意，同时也存在很多问题，所以下面我们就一步步去实现自己的MVP，顺便分析一下可能会导致出问题的一些写法。当然了，100个人就有一百种MVP写法，你开心就好….

## 场景 ##

请求干货集中营的妹纸图片，并将数据显示在RecyclerView上，在这里很感谢干货集中营开放的接口，接口地址：[http://gank.io/api][http_gank.io_api]

## 1.一般的写法 ##

public class MainActivity extends AppCompatActivity { 
        private RecyclerView recyclerView;
        private ImagesAdapter imagesAdapter;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            //初始化控件
            iniViews();
            //加载数据
            getDatas();
        }
    
        private void iniViews() {
            recyclerView = findViewById(R.id.main_recyclerView);
            imagesAdapter = new ImagesAdapter(this, null);
            recyclerView.setLayoutManager(new GridLayoutManager(this, 2));
            recyclerView.setAdapter(imagesAdapter);
        }
    
        private void getDatas() {
            Retrofit retrofit = new Retrofit.Builder()
                    .baseUrl("http://gank.io/api/data/")
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
            NetApiService service = retrofit.create(NetApiService.class);
            Call<ImagesBean> call = service.getImages("福利", "10", "1");
            call.enqueue(new Callback<ImagesBean>() {
                @Override
                public void onResponse(Call<ImagesBean> call, Response<ImagesBean> response) {
                    ImagesBean bean = response.body();
                    List<ImagesBean.ResultsBean> imagesLists = bean.getResults();
                    if(null != imagesLists && imagesLists.size() > 0){
                        imagesAdapter.setDatas(imagesLists);
                    }
                }
    
                @Override
                public void onFailure(Call<ImagesBean> call, Throwable t) {
    
                }
            });
        }
    }

可以看到我们把网络请求以及更新View控件都写在了一起，如果业务很复杂的话，那么一个MainActivity就会出现成百上千行代码，将会把你看得眼花缭乱。那么我们就开始使用MVP模式来进行优化。

## 2.MVP初级使用 ##

### 2.1 View ###

public interface MvpView<T> {
    
        void showProgress();
        void hideProgress();
        void loadSuccess(T t);
        void loadFailure(String msg);
    }

### 2.2 Model ###

public class MvpModel {
        public void request(String category, String count, String pageSize, Callback<ImagesBean> callback){
            Retrofit retrofit = new Retrofit.Builder()
                    .baseUrl("http://gank.io/api/data/")
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
            NetApiService service = retrofit.create(NetApiService.class);
            Call<ImagesBean> call = service.getImages(category, count, pageSize);
            //发起异步请求
            call.enqueue(callback);
        }
    }

### 2.3 Presenter ###

public class MvpPresenter { 
        private MvpView mvpView;
        private MvpModel mvpModel;
    
        public MvpPresenter(MvpView mvpView){
            this.mvpView = mvpView;
            mvpModel = new MvpModel();
        }
    
        public void requstNetDatas(String category, String count, String pageSize){
            //显示加载进度
            mvpView.showProgress();
            mvpModel.request(category, count, pageSize, new Callback<ImagesBean>() {
                @Override
                public void onResponse(Call<ImagesBean> call, Response<ImagesBean> response) {
                    mvpView.loadSuccess(response.body());
                    mvpView.hideProgress();
                }
    
                @Override
                public void onFailure(Call<ImagesBean> call, Throwable t) {
                    mvpView.loadFailure("数据加载失败！");
                    mvpView.hideProgress();
                }
            });
        }
    }

## 2.4 Activity中如何调用 ##

public class MainActivity extends AppCompatActivity implements MvpView<ImagesBean>{ 
        private ProgressDialog progressDialog;
        private RecyclerView recyclerView;
        private ImagesAdapter imagesAdapter;
    
        private MvpPresenter mvpPresenter;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            //初始化控件
            iniViews();
            //初始化Presenter
            mvpPresenter = new MvpPresenter(this);
            //加载数据
            getDatas();
        }
    
        private void getDatas() {
            mvpPresenter.requstNetDatas("福利", "10", "1");
        }
    
        private void iniViews() {
            recyclerView = findViewById(R.id.main_recyclerView);
            imagesAdapter = new ImagesAdapter(this, null);
            recyclerView.setLayoutManager(new GridLayoutManager(this, 2));
            recyclerView.setAdapter(imagesAdapter);
    
            progressDialog = new ProgressDialog(this);
            progressDialog.setCancelable(false);
            progressDialog.setMessage("正在拼命加载中...");
        }
    
        @Override
        public void showProgress() {
            if(!progressDialog.isShowing()){
                progressDialog.show();
            }
        }
    
        @Override
        public void hideProgress() {
            if(progressDialog.isShowing()){
                progressDialog.dismiss();
            }
        }
    
        @Override
        public void loadSuccess(ImagesBean imagesBean) {
            imagesAdapter.setDatas(imagesBean.getResults());
        }
    
        @Override
        public void loadFailure(String msg) {
            Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
        }
    }

这样我们就实现了一个初级版本的MVP模式了，代码感觉清爽多了，Model只负责加载数据，Presenter作为View与Model之间交互的桥梁，Presenter将Model中请求到的结果告诉View，Activity通过实现View接口中的方法去更新数据等等。为什么说这只是一个初级版本呢，试想一下，假设我们在请求网络的过程中由于内存不足，当前的Activity被回收，但是我们的Presenter还持有V层的引用（即对Activity的引用），导致Activity无法被回收，这样就造成了内存泄漏。

## 3.MVP进一步优化 ##

上面说到了当页面关闭了，但Presenter还持有View的引用，导致内存泄漏。解决办法很简单，我们可以进一步优化我们的Presenter

### 3.1 Presenter ###

public class MvpPresenter { 
        private MvpView mvpView;
        private MvpModel mvpModel;
    
        public MvpPresenter(){
            mvpModel = new MvpModel();
        }
    
        /** * 绑定View * @param mvpView */
        public void attachView(MvpView mvpView){
            this.mvpView = mvpView;
        }
    
        /** * 解绑View */
        public void detachView(){
            mvpView = null;
        }
    
        /** * 使用前先检查当前View是否可用 * @return */
        public boolean checkViewAvailable(){
            return mvpView != null;
        }
    
        public void requstNetDatas(String category, String count, String pageSize){
            if(checkViewAvailable()){
                //显示加载进度
                mvpView.showProgress();
                mvpModel.request(category, count, pageSize, new Callback<ImagesBean>() {
                    @Override
                    public void onResponse(Call<ImagesBean> call, Response<ImagesBean> response) {
                        if (checkViewAvailable()) {
                            mvpView.loadSuccess(response.body());
                            mvpView.hideProgress();
                        }
                    }
    
                    @Override
                    public void onFailure(Call<ImagesBean> call, Throwable t) {
                        if (checkViewAvailable()) {
                            mvpView.loadFailure("数据加载失败！");
                            mvpView.hideProgress();
                        }
                    }
                });
            }
        }

主要修改了Presenter的构造器以及添加了绑定View、解绑View/检查当前View是否还可用等几个方法

### 3.2 Activity ###

public class MainActivity extends AppCompatActivity implements MvpView<ImagesBean>{ 
        private ProgressDialog progressDialog;
        private RecyclerView recyclerView;
        private ImagesAdapter imagesAdapter;
    
        private MvpPresenter mvpPresenter;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            //初始化控件
            iniViews();
            //初始化Presenter
            mvpPresenter = new MvpPresenter();
            //绑定View
            mvpPresenter.attachView(this);
            //加载数据
            getDatas();
        }
    
        @Override
        protected void onDestroy() {
            super.onDestroy();
            //页面销毁的时候解绑View
            mvpPresenter.detachView();
        }
    
        private void getDatas() {
            mvpPresenter.requstNetDatas("福利", "10", "1");
        }
    
        private void iniViews() {
            recyclerView = findViewById(R.id.main_recyclerView);
            imagesAdapter = new ImagesAdapter(this, null);
            recyclerView.setLayoutManager(new GridLayoutManager(this, 2));
            recyclerView.setAdapter(imagesAdapter);
    
            progressDialog = new ProgressDialog(this);
            progressDialog.setCancelable(false);
            progressDialog.setMessage("正在拼命加载中...");
        }
    
        @Override
        public void showProgress() {
            if(!progressDialog.isShowing()){
                progressDialog.show();
            }
        }
    
        @Override
        public void hideProgress() {
            if(progressDialog.isShowing()){
                progressDialog.dismiss();
            }
        }
    
        @Override
        public void loadSuccess(ImagesBean imagesBean) {
            imagesAdapter.setDatas(imagesBean.getResults());
        }
    
        @Override
        public void loadFailure(String msg) {
            Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
        }
    }

代码中写了详细的注释，很简单大家都能看懂，这样的话就解决了内存泄漏的问题了，谷歌官方MVP示例demo中是用Fragment来实现View接口，因为Fragment是有生命周期的，所以可以借助Fragment的生命周期，在Activity层关联一个Fragment，在创建Presenter实例的时候将这个Fragment传过去

## 4.MVP继续优化 ##

上面的方式虽然解决了内存泄漏的问题，但是依旧不够优雅，如果每一个Activity都对应一个Model和Presenter的话，试想一下，如果有几百个Activity的话那么是不是也要创建很多个Model和Presenter，关键是很多地方都是重复的可以通用的。所以，创建基类就显得很有必要了

### 4.1 View的基类 ###

这里我们只是简单的定义几个通用的接口方法，比如显示加载进度框、关闭加载框等等  
BaseMvpView

public interface BaseMvpView {
        void showProgressDialog();
        void hideProgressDialog();
    }

### 4.2 Presenter的基类 ###

BaseMvpPresenter

public abstract class BaseMvpPresenter<V extends BaseMvpView> { 
        private V mvpView;
        /** * 绑定View * @param mvpView */
        public void attachView(V mvpView){
            this.mvpView = mvpView;
        }
    
        /** * 解绑View */
        public void detachView(){
            mvpView = null;
        }
    
        /** * 获取View * @return */
        public V getMvpView(){
            return mvpView;
        }
    }

### 4.3 Activity的基类 ###

public abstract class BaseActivity<V extends BaseMvpView, P extends BaseMvpPresenter<V>> extends AppCompatActivity { 
    
        private P presenter;
    
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(getLayoutId());
            //实例化Presenter
            presenter = createPresenter();
            //绑定
            if (presenter != null){
                presenter.attachView((V) this);
            }
            //初始化控件
            iniViews();
            //获取数据
            getRequestDatas();
        }
    
        @Override
        protected void onDestroy() {
            super.onDestroy();
            //解绑
            if (presenter != null){
                presenter.detachView();
            }
        }
    
        protected abstract int getLayoutId();
        protected abstract P createPresenter();
        protected abstract void iniViews();
        protected void getRequestDatas(){}
    
        protected P getPresenter(){
            return presenter;
        }
    }

基类有了，那么针对上面获取妹纸图片数据场景，我们就来写具体的实现类。

MvpPresenterImpl

public class MvpPresenterImpl extends BaseMvpPresenter<MvpViewImpl<ImagesBean>> { 
        private MvpModel mvpModel;
    
        public MvpPresenterImpl(){
            this.mvpModel = new MvpModel();
        }
    
        public void requestNetDatas(String category, String count, String pagesize){
            if (null != getMvpView()) {
                getMvpView().showProgressDialog();
                mvpModel.request(category, count, pagesize, new Callback<ImagesBean>() {
                    @Override
                    public void onResponse(Call<ImagesBean> call, Response<ImagesBean> response) {
                        if (null != getMvpView()) {
                            getMvpView().loadSuccess(response.body());
                            getMvpView().hideProgressDialog();
                        }
                    }
    
                    @Override
                    public void onFailure(Call<ImagesBean> call, Throwable t) {
                        if (null != getMvpView()) {
                            getMvpView().loadFailure("请求失败！");
                            getMvpView().hideProgressDialog();
                        }
                    }
                });
            }
        }
    }

然后就是根据具体的业务场景定义相应的接口了

MvpViewImpl

public interface MvpViewImpl<T> extends BaseMvpView {
    
        /** * 请求成功 * @param data 接口返回的数据 */
        void loadSuccess(T data);
    
        /** * 请求失败 * @param msg 失败原因 */
        void loadFailure(String msg);
    }

最后，我们再来看看Activity类

public class MainActivity extends BaseActivity<MvpViewImpl<ImagesBean>, MvpPresenterImpl> implements MvpViewImpl<ImagesBean>{
        private ProgressDialog progressDialog;
        private RecyclerView recyclerView;
        private ImagesAdapter imagesAdapter;
    
        @Override
        protected int getLayoutId() {
            return R.layout.activity_main;
        }
    
        @Override
        protected void iniViews() {
            recyclerView = findViewById(R.id.main_recyclerView);
            imagesAdapter = new ImagesAdapter(this, null);
            recyclerView.setLayoutManager(new GridLayoutManager(this, 2));
            recyclerView.setAdapter(imagesAdapter);
    
            progressDialog = new ProgressDialog(this);
            progressDialog.setCancelable(false);
            progressDialog.setMessage("正在拼命加载中...");
        }
    
        @Override
        protected void getRequestDatas() {
            //加载数据
            getDatas();
        }
    
        @Override
        protected MvpPresenterImpl createPresenter() {
            return new MvpPresenterImpl();
        }
    
        private void getDatas() {
            getPresenter().requestNetDatas("福利", "10", "1");
        }
    
        @Override
        public void showProgressDialog() {
            if(!progressDialog.isShowing()){
                progressDialog.show();
            }
        }
    
        @Override
        public void hideProgressDialog() {
            if(progressDialog.isShowing()){
                progressDialog.dismiss();
            }
        }
    
        @Override
        public void loadSuccess(ImagesBean data) {
            imagesAdapter.setDatas(data.getResults());
        }
    
        @Override
        public void loadFailure(String msg) {
            Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
        }
    }

当然了，这里只是加载图片，业务比较单一，在activity中直接实现了MvpViewImpl接口，直接明确了泛型类型为ImagesBean实体，业务比较复杂的时候，可能一个页面需要不同的接口得到不同的数据类型，其实我们可以直接这样

public interface MvpViewImpl extends BaseMvpView { 
        //获取到广告位数据
        void loadBannerSuccess(BannerBean bean);
        //获取到推荐数据
        void loadRecommendSuccess(RecommendBean recommendBean);
    }

到此为止简单的封装就完成了，本示例业务比较简单，对于真正项目的话可以视情况扩展。这段时间无意间看到了一个封装的非常不错的一个库，打算利用业余时间好好研究下这个库。下面提供下这个库的地址，大家有兴趣的话也可以去研究研究[https://github.com/JessYanCoding/MVPArms][https_github.com_JessYanCoding_MVPArms]

[Android MVP]: http://blog.csdn.net/u012570402/article/details/51659019
[_MVP]: http://blog.csdn.net/xiaxiazaizai01/article/details/79209288
[http_gank.io_api]: http://gank.io/api
[https_github.com_JessYanCoding_MVPArms]: https://github.com/JessYanCoding/MVPArms