距離上一篇Android MVP從懵逼到入門：登陸業(yè)務(wù)實踐已經(jīng)有一段時間了，這段時間忙著公司的項目，都沒找時間寫寫文章，今天就把這段時間整理的MVP知識再總結(jié)一下，這篇文章主要介紹我是如何使用MVP模式來實現(xiàn)主頁多個Tab切換的場景的。

說是復(fù)雜，其實只是多了一些Fragment而已，在上一篇文章中，我們說Activity的主要作用是創(chuàng)建view和presenter，并把view實例傳入到presenter中，那么，對于多個Tab切換的主頁面（現(xiàn)在的大多數(shù)app都是這樣的主頁），Activity的作用就又多了一個，也是大家都知道的：管理Fragment。其實這沒什么想不到的，在沒說MVP的時候，大家也都是這么做的。

這里我參考網(wǎng)上網(wǎng)友收集的知乎日報的相關(guān)api，使用mvp模式簡單的實現(xiàn)了知乎日報主頁的內(nèi)容。先看一下效果：

主頁效果圖

presenter

先看看presenter怎么寫，應(yīng)該說跟上一篇的實現(xiàn)是一樣的，那就得先寫好契約類--MainContact.java：

public interface MainContract { 
    interface Presenter extends BasePresenter { 
        RootEntity getLatestNews(); 
        RootEntity getSafety(); 
        RootEntity getInterest(); 
        RootEntity getSport(); 
    } 
    interface View extends BaseView<Presenter> { 
        void setTitle(); 
        void refresh(List<StoriesEntity> list); 
    }
}

寫好契約類，那么這個模塊有哪些主要功能基本都清楚了，看view接口，可以知道，頁面可以實現(xiàn)的功能有：

• 1.設(shè)置頁面標(biāo)題--setTitle
• 2.刷新頁面內(nèi)容--refresh

看presenter接口，可以知道，model提供了那些數(shù)據(jù)訪問接口：- 1.獲取今日日報模塊內(nèi)容- 2.獲取網(wǎng)絡(luò)安全模塊內(nèi)容- 3.獲取不許無聊模塊內(nèi)容- 4.獲取體育日報模塊內(nèi)容契約類寫好后，就可以實現(xiàn)presenter接口了，看看MainPresenter.java類：

public class MainPresenter implements MainContract.Presenter {

    private String baseUrl = "http://news-at.zhihu.com";

    private MainContract.View mMainView;
    private Context mContext;

    protected ZhiHuService service;

    public MainPresenter(Context context) {
        this.mContext = context;
    }

    public void setView(MainContract.View view) {
        this.mMainView = view;
        mMainView.setPresenter(this);
        mMainView.setTitle();
        service = getService();
    }

    public ZhiHuService getService() {
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                .build();
        service = retrofit.create(ZhiHuService.class);
        return service;
    }

    @Override
    public RootEntity getLatestNews() {
        return loadData(service.getLatestNews());
    }

    @Override
    public RootEntity getSafety() {
        return loadData(service.getSafety());
    }

    @Override
    public RootEntity getInterest() {
        return loadData(service.getInterest());
    }

    @Override
    public RootEntity getSport() {
        return loadData(service.getSport());
    }

    @Override
    public void start() {

    }

    public RootEntity loadData(Observable<RootEntity> observable) {
        final RootEntity rootEntity = new RootEntity();
        observable.observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io())
                .map(new Func1<RootEntity, ArrayList<StoriesEntity>>() {
                    @Override
                    public ArrayList<StoriesEntity> call(RootEntity rootEntity) {
                        return rootEntity.getStories();
                    }
                })
                .subscribe(new Subscriber<ArrayList<StoriesEntity>>() {
                    @Override
                    public void onCompleted() {

                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onNext(ArrayList<StoriesEntity> storiesEntities) {
                        rootEntity.setStories(storiesEntities);
                        mMainView.refresh(storiesEntities);
                    }
                });

        return rootEntity;
    }
}

view

view其實才是這篇文章的主題，契約類里面定義的一些接口其實是所有的view實現(xiàn)類的集合，比如這里有4個Fragment頁面，每個頁面展示的內(nèi)容是不一樣的，需要的接口也不一樣，這些接口都需要在契約類里面定義，然后每個Fragment都去實現(xiàn)這個接口，完成對應(yīng)接口中的內(nèi)容。

比如這4個Fragment都去實現(xiàn)MainContract.View，各自都實現(xiàn)setTitle和refresh內(nèi)容，如何還有其他需要實現(xiàn)的接口，同樣定義在契約類里面，誰關(guān)心這個接口，誰就去實現(xiàn)這個接口，view不必關(guān)心接口的調(diào)用，只需要實現(xiàn)內(nèi)容就行了，這在MVP中體現(xiàn)的比較明顯：面向接口編程。（我所接觸的面向接口編程的另一種場景就是模塊化編程，感覺有些類似。）

既然有4個Fragment，那么他們肯定有共同之處，至少他們都是Fragment，何不提取基類呢？這相比大家都能想到--Java語言的三大特性即：封裝、繼承、多態(tài)。

來看看BaseFragment的內(nèi)容：

public class BaseFragment extends Fragment implements MainContract.View {

    @BindView(R.id.lv_news)
    ListView mListView;

    protected MainContract.Presenter mPresenter;
    protected ActionBar mActionBar;
    private ZhiHuNewsAdapter mAdapter;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_main_0, container, false);
        ButterKnife.bind(this, view);

        return view;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        mAdapter = new ZhiHuNewsAdapter(getContext());
        mListView.setAdapter(mAdapter);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        if (isAdded()) {
            mActionBar = ((AppCompatActivity)getActivity()).getSupportActionBar();
            setTitle();
        }
    }

    @Override
    public void setPresenter(MainContract.Presenter presenter) {
        this.mPresenter = presenter;
    }

    @Override
    public void refresh(final List<StoriesEntity> list) {
        mAdapter.setNewsList(list);
        mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Intent intent = new Intent(getActivity(), StoryDetailActivity.class);
                intent.putExtra(StoryDetailFragment.STORY_ID, list.get(position).getId());
                intent.putExtra(StoryDetailFragment.STORY_TITLE, list.get(position).getTitle());
                startActivity(intent);
            }
        });
    }

    @Override
    public void setTitle() {
        if (mActionBar != null) {
            mActionBar.setTitle(R.string.app_name);
        }
    }
}

model

因為這里沒有考慮到數(shù)據(jù)的持久化，沒有創(chuàng)建本地數(shù)據(jù)庫，所以，model的實現(xiàn)其實就是一個service，因為是用reftrofit2來完成網(wǎng)絡(luò)請求的，所以，model就是ZhiHuService.java：

public interface ZhiHuService {

    //今日頭條
    @GET("/api/4/news/latest")
    Observable<RootEntity> getLatestNews();

    //互聯(lián)網(wǎng)安全
    @GET("/api/4/theme/10")
    Observable<RootEntity> getSafety();

    //不準(zhǔn)無聊
    @GET("/api/4/theme/11")
    Observable<RootEntity> getInterest();

    //體育日報
    @GET("/api/4/theme/8")
    Observable<RootEntity> getSport();
}

avtivity

最后看看activity，作用有三個：創(chuàng)建view（這里是views）、創(chuàng)建presenter、管理fragemnt：

public class MainActivity extends AppCompatActivity {

    @BindView(R.id.tab_item_main_0)
    TabItem tabItemMain0;

    @BindView(R.id.tab_item_main_1)
    TabItem tabItemMain1;

    @BindView(R.id.tab_item_main_2)
    TabItem tabItemMain2;

    @BindView(R.id.tab_item_main_3)
    TabItem tabItemMain3;

    @BindView(R.id.tab_item_main_4)
    TabItem tabItemMain4;

    @BindView(R.id.toolbar)
    Toolbar toolbar;

    @BindView(R.id.fab)
    FloatingActionButton floatingBar;

    private FragmentManager mFragmentManager;
    private TodayFragment mTodayFragment;
    private InterestFragment mInterestFragment;
    private SafetyFragment mSafetyFragment;
    private SportFragment mSportFragment;
    private OtherFragment mOtherFragment;

    private MainPresenter mPresenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);

        mFragmentManager = getSupportFragmentManager();
        setSupportActionBar(toolbar);

        mPresenter = new MainPresenter(getApplicationContext());

        tabItemMain0.performClick();
    }

    public void showFragment(int tag) {
        if (mFragmentManager != null) {
            FragmentTransaction transaction = mFragmentManager.beginTransaction();
            hideFragments();
            switch (tag) {
                case TagStatic.TAG_FRAGMENT_TODAY:
                    mTodayFragment = (TodayFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_TODAY + "");
                    if (mTodayFragment == null) {
                        mTodayFragment = new TodayFragment();
                        transaction.add(R.id.fragment_content, mTodayFragment, tag + "");
                    } else {
                        transaction.show(mTodayFragment);
                    }
                    mPresenter.setView(mTodayFragment);
                    break;

                case TagStatic.TAG_FRAGMENT_INTEREST:
                    mInterestFragment = (InterestFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_INTEREST + "");
                    if (mInterestFragment == null) {
                        mInterestFragment = new InterestFragment();
                        transaction.add(R.id.fragment_content, mInterestFragment, tag + "");
                    } else {
                        transaction.show(mInterestFragment);
                    }
                    mPresenter.setView(mInterestFragment);
                    break;

                case TagStatic.TAG_FRAGMENT_SAFETY:
                    mSafetyFragment = (SafetyFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_SAFETY + "");
                    if (mSafetyFragment == null) {
                        mSafetyFragment = new SafetyFragment();
                        transaction.add(R.id.fragment_content, mSafetyFragment, tag + "");
                    } else {
                        transaction.show(mSafetyFragment);
                    }
                    mPresenter.setView(mSafetyFragment);
                    break;

                case TagStatic.TAG_FRAGMENT_SPORT:
                    mSportFragment = (SportFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_SPORT + "");
                    if (mSportFragment == null) {
                        mSportFragment = new SportFragment();
                        transaction.add(R.id.fragment_content, mSportFragment, tag + "");
                    } else {
                        transaction.show(mSportFragment);
                    }
                    mPresenter.setView(mSportFragment);
                    break;

                case TagStatic.TAG_FRAGMENT_OTHER:
                    mOtherFragment = (OtherFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_OTHER + "");
                    if (mOtherFragment == null) {
                        mOtherFragment = new OtherFragment();
                        transaction.add(R.id.fragment_content, mOtherFragment, tag + "");
                    } else {
                        transaction.show(mOtherFragment);
                    }
                    mPresenter.setView(mOtherFragment);
                    break;
            }

            transaction.commitAllowingStateLoss();
        }
    }

    private void hideFragments() {
        FragmentTransaction transaction = mFragmentManager.beginTransaction();
        mTodayFragment = (TodayFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_TODAY + "");
        if (mTodayFragment != null) {
            transaction.hide(mTodayFragment);
        }

        mInterestFragment = (InterestFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_INTEREST + "");
        if (mInterestFragment != null) {
            transaction.hide(mInterestFragment);
        }

        mSafetyFragment = (SafetyFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_SAFETY + "");
        if (mSafetyFragment != null) {
            transaction.hide(mSafetyFragment);
        }

        mSportFragment = (SportFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_SPORT + "");
        if (mSportFragment != null) {
            transaction.hide(mSportFragment);
        }

        mOtherFragment = (OtherFragment) mFragmentManager.findFragmentByTag(TagStatic.TAG_FRAGMENT_OTHER + "");
        if (mOtherFragment != null) {
            transaction.hide(mOtherFragment);
        }

        transaction.commitAllowingStateLoss();
    }

    @OnClick({R.id.tab_item_main_0, R.id.tab_item_main_1, R.id.tab_item_main_2,
            R.id.tab_item_main_3, R.id.tab_item_main_4, R.id.fab})
    public void onClick(View view) {
        clearChecked();
        switch (view.getId()) {
            case R.id.tab_item_main_0:
                tabItemMain0.setChecked(true);
                showFragment(TagStatic.TAG_FRAGMENT_TODAY);
                break;

            case R.id.tab_item_main_1:
                tabItemMain1.setChecked(true);
                showFragment(TagStatic.TAG_FRAGMENT_INTEREST);
                break;

            case R.id.tab_item_main_2:
                tabItemMain2.setChecked(true);
                showFragment(TagStatic.TAG_FRAGMENT_SAFETY);
                break;

            case R.id.tab_item_main_3:
                tabItemMain3.setChecked(true);
                showFragment(TagStatic.TAG_FRAGMENT_SPORT);
                break;

            case R.id.tab_item_main_4:
                tabItemMain4.setChecked(true);
                showFragment(TagStatic.TAG_FRAGMENT_OTHER);
                break;

            case R.id.fab:
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_SHORT)
                        .setAction("Action", null).show();
                break;
        }
    }

    private void clearChecked() {
        tabItemMain0.setChecked(false);
        tabItemMain1.setChecked(false);
        tabItemMain2.setChecked(false);
        tabItemMain3.setChecked(false);
        tabItemMain4.setChecked(false);
    }
}

avtivity里的內(nèi)容還是比較少的，只是多了Fragment的顯示和隱藏，沒有變得復(fù)雜和職責(zé)不清，對于管理和維護也很簡單。因為有多個view實現(xiàn)類，所以，我沒有在presenter的初始化時傳入view實例，而是通過在presenter中的setView方法設(shè)置不同的view。

跟retrofit2相關(guān)的內(nèi)容這里不展開說，不知道的、想了解的可以自行搜索，這里是GitHub地址：retrofit，以及本文的項目源碼：Login-MVP-Architecture ，希望對MVP感興趣以及任何想要一起提高Android開發(fā)技能的小伙伴能star一下，以后會繼續(xù)在這個項目上添加新的內(nèi)容，包括一些有用的工具類、各種控件、效果實現(xiàn)、設(shè)計模式的使用等等。

周末愉快(●'?'●)