什么是MVP，为什么要用MVP？
网上介绍MVP的很多，百度一下你就知道，至于为什么要用MVP，当然是由于它的优势了：
1.代码简洁
此处的简洁是逻辑的简洁，而不是代码本身 举个栗子

image

比如购物车界面，有很多请求网络的地方：获取购物车商品列表、购物车商品的删除、购物车商品的购买等等， 这么多网络请求，如果都写在一个Activity，而且还有大量逻辑判断，那这个Activity的行数~ 看着就让人头痛， 即便写了注释，维护起来也是比较麻烦的
2.降低耦合，方便维护
MVP的使用，使Activity中的网络请求剥离出来 成为model、presenter，model只负责网络的请求、pesenter负责处理请求网络后的数据处理：加载中 成功 or 失败 取消加载；最后View进行界面的展示

整体的mvp结构图

image.png

Start：介绍一下BaseMvpActivity

MVP的Activity基类：纯粹的 MVP 包装，不要增加任何View层基础功能 如果要添加基类功能，建议写一个所有activity的基类添加

public abstract class BaseMvpActivity<P extends IPresenter> extends Activity implements BaseView {

    protected P mPresenter;

    protected abstract P createPresenter();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mPresenter = createPresenter();
        if (mPresenter == null) {
            throw new NullPointerException("Presenter is null! Do you return null in createPresenter()?");
        }
        mPresenter.onMvpAttachView(this, savedInstanceState);
    }

    @Override
    protected void onStart() {
        super.onStart();
        if (mPresenter != null) {
            mPresenter.onMvpStart();
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        if (mPresenter != null) {
            mPresenter.onMvpResume();
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (mPresenter != null) {
            mPresenter.onMvpPause();
        }
    }

    @Override
    protected void onStop() {
        super.onStop();
        if (mPresenter != null) {
            mPresenter.onMvpStop();
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        if (mPresenter != null) {
            mPresenter.onMvpSaveInstanceState(outState);
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (mPresenter != null) {
            mPresenter.onMvpDetachView(false);
            mPresenter.onMvpDestroy();
        }
    }

}

在这里有人会觉得生命周期怎么会出现onMvpStart 或者onMvpResume等等
下面来解释一下MVP的生命周期：
就是为了定义P层生命周期与 V层同步

public interface IPresenter<V extends BaseView> {

    void onMvpAttachView(V view, Bundle savedInstanceState);

    void onMvpStart();

    void onMvpResume();

    void onMvpPause();

    void onMvpStop();

    void onMvpSaveInstanceState(Bundle savedInstanceState);

    void onMvpDetachView(boolean retainInstance);

    void onMvpDestroy();
}

接下来 我们会用到WeakReference类从字面上了解 他的意思是弱引用

关于 弱引用，强引用、软引用、虚引用，可以参考
https://www.cnblogs.com/gudi/p/6403953.html

public class BasePresenter<V extends BaseView> implements IPresenter<V> {

    private WeakReference<V> viewRef;

    protected V getView() {
        return viewRef.get();
    }

    protected boolean isViewAttached() {
        return viewRef != null && viewRef.get() != null;
    }

    private void attach(V view, Bundle savedInstanceState) {
        viewRef = new WeakReference<V>(view);
    }

    @Override
    public void onMvpAttachView(V view, Bundle savedInstanceState) {
        attach(view, savedInstanceState);
    }

    @Override
    public void onMvpStart() {

    }

    @Override
    public void onMvpResume() {

    }

    @Override
    public void onMvpPause() {

    }

    @Override
    public void onMvpStop() {

    }

    @Override
    public void onMvpSaveInstanceState(Bundle savedInstanceState) {

    }

    private void _detach(boolean retainInstance) {
        if (viewRef != null) {
            viewRef.clear();
            viewRef = null;
        }
    }

    @Override
    public void onMvpDetachView(boolean retainInstance) {
        _detach(retainInstance);
    }

    @Override
    public void onMvpDestroy() {

    }
}

接下来就是 view和model绑定处理数据

public class MainPresenterImpl extends BasePresenter<MainContract.IMainView> implements MainContract.IMainPresenter {
    private LoginMobel mMobel;

    public MainPresenterImpl() {
        mMobel = new LoginMobel();
    }


    @Override
    public void main(String username, String password, String token) {
        //先进行非空判断
        if (isViewAttached()) {
            handleLogin(getView(), username, password, token);
        }
    }

    @Override
    public void login(String username, String password, String token) {
        //先进行非空判断
        if (isViewAttached()) {
         Login(getView(), username, password, token);
        }
    }

    private void Login(final MainContract.IMainView view, String username, String password, String token) {
        mMobel.login(username, password, token, new StringCallbackAdapter() {
            @Override
            public void onError(Call call, Exception e, int id) {
                super.onError(call, e, id);
                view.loginSuccess();
            }

            @Override
            public void onResponse(String response, int id) {
                super.onResponse(response, id);
                view.loginFailed(response);
            }
        });
    }


    private void handleLogin(final MainContract.IMainView view, String username, String password, String token) {
        mMobel.login(username, password, token, new StringCallbackAdapter() {
            @Override
            public void onError(Call call, Exception e, int id) {
                super.onError(call, e, id);
                view.mainSuccess();
            }

            @Override
            public void onResponse(String response, int id) {
                super.onResponse(response, id);
                view.mainFailed(response);
            }
        });
    }
}

使用

public class MainActivity extends BaseMvpActivity<MainContract.IMainPresenter> implements MainContract.IMainView {
  @Override
    protected MainContract.IMainPresenter createPresenter() {
        return new MainPresenterImpl();
    }

 mPresenter.main(username, password, token);

  @Override
    public void mainSuccess() {
        Toast.makeText(this, "mainSuccess", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void mainFailed(String msg) {
        Toast.makeText(this, "mainFailed", Toast.LENGTH_SHORT).show();
    }

时间有限，暂时就先这样，具体可下载Demo查看 ↓

本Demo：https://gitee.com/oubajunping/androidzhimvprumen
MVP快速生成类的插件： https://github.com/githubwing/MVPHelper