MVP模式在Android中的使用

转自：http://blog.youkuaiyun.com/feiduclear_up/article/details/46374653   废墟的树

前一篇文章中学习了MVC框架模式在Android中的使用，不了解什么是MVC框架模式的亲戳这里 框架模式 MVC 在Android中的使用。其实谷歌Android开发团队是鼓励开发者利用MVC框架模式开发项目的，我们平时写代码也或多或少的在使用MVC框架模式开发项目，比如说谷歌自己退出来的Volley网络请求框架就是遵循MVC框架的。我们可以理解为Volley框架是MVC当中的模型，也就是网络数据处理这一块，无需跟View视图有任何关联。也符合视图和模型分离。可能你会觉得MVC框架已经很好用了，也能满足任何项目开发，不错，可是从上一篇博客你会发现，Controller控制器和View视图显示是在一个类Activity中体现出来的，而Android中Activity是担当Controller控制器的角色的，如果界面操作方式繁琐，视图显示复杂，那么我们不得不在Activity中添加更多的View视图显示操作，这样自然增加了Activity的代码量，也导致了Activity承担的任务和逻辑处理太多，职责不清晰。这一篇我们来介绍另外一种框架模式MVP。

MVP

MPV 是从经典的MVC模式演变过来的，其基本思路都是相通的。其中M是model模型，提供业务数据；P和MVC中的C担当的角色相似，是Presenter控制者，进行逻辑处理。V是View视图，显示数据。MVP与MVC有着一个重大的区别：在MVP中View并不直接使用Model，它们之间的通信是通过Presenter (MVC中的Controller)来进行的，所有的交互都发生在Presenter内部，而在MVC中View会从直接Model中读取数据而不是通过 Controller。

MVC框架图
MVP框架图

从上面的框架图可以看出MVC和MVP最大的区别就是 Model和View之间的关系。在MVC框架中，View是可以直接读取Model模型中的数据的，Model模型数据发生改变是会通知View数据显示发生相应的改变。而在MVP中Model和View之间的没有任何联系，是两个完全独立的模块，当Model模型发生数据改变时，通过Presenter通知View视图发生相应的UI改变。因此，个人觉得：MVP才是正真的视图和模型完全分离，也就是Model模型进行业务数据处理和View视图显示没有任何关联。

MVP for Android

在Andorid项目中，我们习惯将Activity作为MVC中的控制者来达到Model模型和View视图分离，但是在MVP框架模式中，通常将Activity作为View视图层，因为在MVC框架模式中Activity和View视图显示关联紧密，Activity中包含大量的View视图显示代码，如果哪天老板说需要修改View视图显示，这时候你是不是感觉需要修改Activity中的大量代码？这么一来会将Activity中控制逻辑破坏，也导致Activity中承担太多的职责。根据单一职责原则，Activity主要起到用户交互作用，也就是接收用户输入，显示请求结果。因此可以通过MVP框架模式来减轻Activity的职责。看看Android项目中怎么实现吧！

同样拿上一篇的天气预报小项目来举例子：

Model模型

和MVC框架模式一样，Model模型处理数据代码不变

<code class="hljs java has-numbering"><span class="hljs-javadoc">/**
 * Created by xjp 2015-6-7
 * 天气Model接口
 */</span>
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">WeatherModel</span> {</span>
    <span class="hljs-keyword">void</span> loadWeather(String cityNO, OnWeatherListener listener);
}
.........

<span class="hljs-javadoc">/**
 * Created by xjp on 2015/6/7.
 * 天气Model实现
 */</span>
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">WeatherModelImpl</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WeatherModel</span> {</span>
    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">loadWeather</span>(String cityNO, <span class="hljs-keyword">final</span> OnWeatherListener listener) {
        <span class="hljs-comment">/*数据层操作*/</span>
        VolleyRequest.newInstance().newGsonRequest(<span class="hljs-string">"http://www.weather.com.cn/data/sk/"</span> + cityNO + <span class="hljs-string">".html"</span>,
                Weather.class, <span class="hljs-keyword">new</span> Response.Listener<Weather>() {
                    <span class="hljs-annotation">@Override</span>
                    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onResponse</span>(Weather weather) {
                        <span class="hljs-keyword">if</span> (weather != <span class="hljs-keyword">null</span>) {
                            listener.onSuccess(weather);
                        } <span class="hljs-keyword">else</span> {
                            listener.onError();
                        }
                    }
                }, <span class="hljs-keyword">new</span> Response.ErrorListener() {
                    <span class="hljs-annotation">@Override</span>
                    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onErrorResponse</span>(VolleyError error) {
                        listener.onError();
                    }
                });
    }
}</code>

通过OnWeatherListener接口回调将Model模型处理的数据返回给Presenter控制者。

Presenter控制器

<code class="hljs java has-numbering"><span class="hljs-javadoc">/**
 * Created by xjp on 2015/6/7.
 * 天气 Presenter接口
 */</span>
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">WeatherPresenter</span> {</span>
    <span class="hljs-javadoc">/**
     * 获取天气的逻辑
     */</span>
    <span class="hljs-keyword">void</span> getWeather(String cityNO);

}
..........


<span class="hljs-javadoc">/**
 * Created by xjp on 2015/6/7.
 * 在Presenter层实现，给Model层回调，更改View层的状态，确保Model层不直接操作View层
 */</span>
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">OnWeatherListener</span> {</span>
    <span class="hljs-javadoc">/**
     * 成功时回调
     *
     *<span class="hljs-javadoctag"> @param</span> weather
     */</span>
    <span class="hljs-keyword">void</span> onSuccess(Weather weather);
    <span class="hljs-javadoc">/**
     * 失败时回调，简单处理，没做什么
     */</span>
    <span class="hljs-keyword">void</span> onError();

}

.........

<span class="hljs-keyword">package</span> org.rocko.demos.mvp.presenter.impl;

<span class="hljs-keyword">import</span> org.rocko.demos.mvp.model.WeatherModel;
<span class="hljs-keyword">import</span> org.rocko.demos.mvp.model.entity.Weather;
<span class="hljs-keyword">import</span> org.rocko.demos.mvp.model.impl.WeatherModelImpl;
<span class="hljs-keyword">import</span> org.rocko.demos.mvp.presenter.OnWeatherListener;
<span class="hljs-keyword">import</span> org.rocko.demos.mvp.presenter.WeatherPresenter;
<span class="hljs-keyword">import</span> org.rocko.demos.mvp.ui.view.WeatherView;

<span class="hljs-javadoc">/**
 * Created by xjp on 2015/6/7.
 * 天气 Presenter实现
 */</span>
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">WeatherPresenterImpl</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WeatherPresenter</span>, <span class="hljs-title">OnWeatherListener</span> {</span>
    <span class="hljs-comment">/*Presenter作为中间层，持有View和Model的引用*/</span>
    <span class="hljs-keyword">private</span> WeatherView weatherView;
    <span class="hljs-keyword">private</span> WeatherModel weatherModel;

    <span class="hljs-keyword">public</span> <span class="hljs-title">WeatherPresenterImpl</span>(WeatherView weatherView) {
        <span class="hljs-keyword">this</span>.weatherView = weatherView;
        weatherModel = <span class="hljs-keyword">new</span> WeatherModelImpl();
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">getWeather</span>(String cityNO) {
        weatherView.showLoading();
        weatherModel.loadWeather(cityNO, <span class="hljs-keyword">this</span>);
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onSuccess</span>(Weather weather) {
        weatherView.hideLoading();
        weatherView.setWeatherInfo(weather);
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onError</span>() {
        weatherView.hideLoading();
        weatherView.showError();
    }
}
</code>

从代码中我们可以看到Presenter控制器同时持有 WeatherModel和WeatherView对象且实现了OnWeatherListener接口取回Model模型数据，因此，WeatherPresenterImpl向WeatherModel发送数据请求，然后通过OnWeatherListener接口实现获取请求结果，在将结果通过接口WeatherView把数据显示到Activity担当的View视图中。从而达到彻底将Model和View完全分离，试想在这种情况下，如果你需要修改Model是完全不会影响View视图代码的修改的，同理，修改View视图层的时候，也完全无需修改Model层。相当于Model和View互相不知道对方的存在，都是通过中间控制器Presenter来传达通信。

View视图

先定义一个View视图显示的接口WeatherView

<code class="hljs java has-numbering"><span class="hljs-javadoc">/**
 * Created by xjp on 2015/6/7.
 */</span>
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">WeatherView</span> {</span>
    <span class="hljs-keyword">void</span> showLoading();

    <span class="hljs-keyword">void</span> hideLoading();

    <span class="hljs-keyword">void</span> showError();

    <span class="hljs-keyword">void</span> setWeatherInfo(Weather weather);
}
</code>

然后实现Activity实现WeatherView接口

<code class="hljs java has-numbering"><span class="hljs-javadoc">/**
 * 天气界面
 */</span>
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">WeatherActivity</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">BaseActivity</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WeatherView</span>, <span class="hljs-title">View</span>.<span class="hljs-title">OnClickListener</span> {</span>
    <span class="hljs-keyword">private</span> Dialog loadingDialog;
    <span class="hljs-keyword">private</span> EditText cityNOInput;
    <span class="hljs-keyword">private</span> TextView city;
    <span class="hljs-keyword">private</span> TextView cityNO;
    <span class="hljs-keyword">private</span> TextView temp;
    <span class="hljs-keyword">private</span> TextView wd;
    <span class="hljs-keyword">private</span> TextView ws;
    <span class="hljs-keyword">private</span> TextView sd;
    <span class="hljs-keyword">private</span> TextView wse;
    <span class="hljs-keyword">private</span> TextView time;
    <span class="hljs-keyword">private</span> TextView njd;

    <span class="hljs-keyword">private</span> WeatherPresenter weatherPresenter;

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onCreate</span>(Bundle savedInstanceState) {
        <span class="hljs-keyword">super</span>.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();

    }

    <span class="hljs-keyword">private</span> <span class="hljs-keyword">void</span> <span class="hljs-title">init</span>() {
        cityNOInput = findView(R.id.et_city_no);
        city = findView(R.id.tv_city);
        cityNO = findView(R.id.tv_city_no);
        temp = findView(R.id.tv_temp);
        wd = findView(R.id.tv_WD);
        ws = findView(R.id.tv_WS);
        sd = findView(R.id.tv_SD);
        wse = findView(R.id.tv_WSE);
        time = findView(R.id.tv_time);
        njd = findView(R.id.tv_njd);

        findView(R.id.btn_go).setOnClickListener(<span class="hljs-keyword">this</span>);

        weatherPresenter = <span class="hljs-keyword">new</span> WeatherPresenterImpl(<span class="hljs-keyword">this</span>); <span class="hljs-comment">//传入WeatherView</span>
        loadingDialog = <span class="hljs-keyword">new</span> ProgressDialog(<span class="hljs-keyword">this</span>);
        loadingDialog.setTitle(<span class="hljs-string">"加载天气中..."</span>);
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onClick</span>(View v) {
        <span class="hljs-keyword">switch</span> (v.getId()) {
            <span class="hljs-keyword">case</span> R.id.btn_go:
                weatherPresenter.getWeather(cityNOInput.getText().toString().trim());
                <span class="hljs-keyword">break</span>;
        }
    }


    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">showLoading</span>() {
        loadingDialog.show();
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">hideLoading</span>() {
        loadingDialog.dismiss();
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">showError</span>() {
        <span class="hljs-comment">//Do something</span>
        Toast.makeText(getApplicationContext(), <span class="hljs-string">"error"</span>, Toast.LENGTH_SHORT).show();
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setWeatherInfo</span>(Weather weather) {
        WeatherInfo info = weather.getWeatherinfo();
        city.setText(info.getCity());
        cityNO.setText(info.getCityid());
        temp.setText(info.getTemp());
        wd.setText(info.getWD());
        ws.setText(info.getWS());
        sd.setText(info.getSD());
        wse.setText(info.getWS());
        time.setText(info.getTemp());
        njd.setText(info.getNjd());
    }

}
</code>

因此，Activity及从MVC中的Controller中解放出来了，这会Activity主要做显示View的作用和用户交互。每个Activity可以根据自己显示View的不同实现View视图接口WeatherView。

总结

1. MVP框架模式完全将Model模型和View视图分离，从而使得代码的耦合性第，利用MVP框架写项目达到解耦作用。
2. MVP和MVC最大的区别是:MVC中的V可以从M中获取数据，而MVP中M和V完全分离，互相不知道对方的存在，Presenter通过接口通信方式将V和M通信。
3. 在Android中MVP框架 Activity担当View视图层和MVC框架模式不一样Activity担当控制器。

源码地址下载：源码地址