擁有生命週期的Presenter的MVP框架，支援Multi P

結合自己對MVP的理解，加上個人習慣，整理出這麼一份Android MVP框架

• 通過註解動態注入Presenter
• Presenter擁有完整生命週期
• 支援多Presenter注入
• 狀態復原

0x00 前言

此框架可以說是Fork nucleus 而來，只不過結合了個人理解和習慣進行更改，放上此框架連結 github.com/izyhang/Dam…

0x01 介紹

先介紹一下Damon的簡單使用

新建View、Presenter

Presenter具有與Activity一樣的生命週期，這裡展示部分生命週期

interface MainView {
    fun log(msg: String)
}

class MainPresenter : BasePresenter<MainView>() {
    override fun onCreate(arguments: Bundle?, savedState: Bundle?) {
        super.onCreate(arguments, savedState)
        view.log("MainPresenter.onCreate")
    }

    override fun onResume() {
        super.onResume()
        view.log("MainPresenter.onResume")
    }

    override fun onPause() {
        super.onPause()
        view.log("MainPresenter.onPause")
    }

    override fun onDestroy() {
        super.onDestroy()
        view.log("MainPresenter.onDestroy")
    }
}
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修改MainActivity

為MainActivity繫結Presenter，想要拿到Presenter通過@BindPresenter獲取

@RequiresPresenter(MainPresenter::class)
class MainActivity : BaseActivity(), MainView {
    @BindPresenter
    private var mainPresenter: MainPresenter? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        mainPresenter.xxx()
    }

    override fun log(msg: String) {
        println(msg)
    }
}
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多Presenter注入

@RequiresPresenter(value = [MainPresenter::class, SecondPresenter::class])
class MainActivity : BaseActivity(), MainView, SecondView {
    @BindPresenter
    private var mainPresenter: MainPresenter? = null
    @BindPresenter
    private var secondPresenter: SecondPresenter? = null

    override fun log(msg: String) {
        println(msg)
    }
}
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0x02 工作原理

下面介紹一下Damon的工作原理

Presenter的動態注入和賦值

用註解代替手動例項化Presenter更加方便，並且在封裝好的Activity實現了狀態恢復，避免重複建立Presenter

在介面建立之時會傳入當前class到ReflectionPresenterFactory，通過cls.getAnnotation拿到@RequiresPresenter註解並儲存，在這裡也對當前class有@BindPresenter註解的成員進行儲存

@Nullable
public static ReflectionPresenterFactory fromViewClass(Object host, Class<?> cls) {
    RequiresPresenter annotation = cls.getAnnotation(RequiresPresenter.class);
    Class<? extends MvpPresenter>[] pClass = null != annotation ? annotation.value() : null;
    if (null == pClass) {
        return null;
    }
    List<Field> fields = new ArrayList<>();
    for (Field field : cls.getDeclaredFields()) {
        Annotation[] annotations = field.getDeclaredAnnotations();
        if (annotations.length < 1) {
            continue;
        }
        if (annotations[0] instanceof BindPresenter) {
            fields.add(field);
        }
    }
    return new ReflectionPresenterFactory(host, pClass, fields);
}
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Presenter的建立

上面講過Damon的Presenter是具有完整生命週期的，看到封裝的Activity MvpAppCompatActivity.java

在Activity的生命週期通過PresenterLifecycleDelegate去控制Presenter的方法呼叫，賦予其生命週期。其中還過載了onSaveInstanceState輔助Presenter狀態恢復機制

public class MvpAppCompatActivity extends AppCompatActivity implements MvpView {

    private static final String PRESENTER_STATE_KEY = "presenter_state";
    private PresenterLifecycleDelegate mPresenterDelegate =
            new PresenterLifecycleDelegate(ReflectionPresenterFactory.fromViewClass(this, getClass()));

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mPresenterDelegate.onCreate(this, getIntent().getExtras(), null != savedInstanceState ? savedInstanceState.getBundle(PRESENTER_STATE_KEY) : null);
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putBundle(PRESENTER_STATE_KEY, mPresenterDelegate.onSaveInstanceState());
    }

    @Override
    public void onStart() {
        super.onStart();
        mPresenterDelegate.onStart();
    }

    @Override
    public void onResume() {
        super.onResume();
        mPresenterDelegate.onResume();
    }

    @Override
    public void onPause() {
        mPresenterDelegate.onPause();
        super.onPause();
    }

    @Override
    public void onStop() {
        mPresenterDelegate.onStop();
        super.onStop();
    }

    @Override
    public void onDestroy() {
        mPresenterDelegate.onDestroy(!isChangingConfigurations());
        super.onDestroy();
    }
}
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PresenterLifecycleDelegate

最重要的就是此類，連線Activity和Presenter的樞紐，控制Presenter的建立、恢復、生命週期

public class PresenterLifecycleDelegate {

    private static final String PRESENTER_KEY = "presenter - ";
    private static final String PRESENTER_ID_KEYS = "presenter_ids";

    @Nullable
    private PresenterFactory mPresenterFactory;
    @Nullable
    private List<? extends MvpPresenter> mPresenters;

    private boolean mPresenterHasView;

    public PresenterLifecycleDelegate(@Nullable PresenterFactory presenterFactory) {
        this.mPresenterFactory = presenterFactory;
    }

    public void onCreate(MvpView view, @Nullable Bundle arguments, @Nullable Bundle savedState) {
        if (mPresenterFactory == null) {
            return;
        }
        Bundle presenterBundle = null;
        if (savedState != null) {
            presenterBundle = ParcelFn.unmarshall(ParcelFn.marshall(savedState));
        }
        createPresenter(presenterBundle);
        if (mPresenters != null && !mPresenters.isEmpty()) {
            mPresenterFactory.bindPresenter(mPresenters);
            for (MvpPresenter presenter : mPresenters) {
                //noinspection unchecked
                presenter.create(view, arguments, null != presenterBundle ? presenterBundle.getBundle(PRESENTER_KEY.concat(presenter.getClass().getSimpleName())) : null);
            }
        }
    }

    private void createPresenter(Bundle presenterBundle) {
        if (presenterBundle != null) {
            mPresenters = PresenterStorage.INSTANCE.getPresenter(presenterBundle.getStringArray(PRESENTER_ID_KEYS));
        }

        if (mPresenters == null) {
            //noinspection ConstantConditions
            mPresenters = mPresenterFactory.createPresenter();
            PresenterStorage.INSTANCE.add(mPresenters);
        }
    }

    public void onStart() {
        if (mPresenters != null && !mPresenters.isEmpty()) {
            for (MvpPresenter presenter : mPresenters) {
                presenter.start();
            }
        }
    }

    public Bundle onSaveInstanceState() {
        Bundle bundle = new Bundle();
        if (mPresenters != null && !mPresenters.isEmpty()) {
            String[] ids = new String[mPresenters.size()];
            for (MvpPresenter presenter : mPresenters) {
                Bundle presenterBundle = new Bundle();
                presenter.save(presenterBundle);
                bundle.putBundle(PRESENTER_KEY.concat(presenter.getClass().getSimpleName()), presenterBundle);

                ids[mPresenters.indexOf(presenter)] = PresenterStorage.INSTANCE.getId(presenter);
            }
            bundle.putStringArray(PRESENTER_ID_KEYS, ids);
        }
        return bundle;
    }

    public void onResume() {
        if (mPresenters != null && !mPresenters.isEmpty() && !mPresenterHasView) {
            for (MvpPresenter presenter : mPresenters) {
                presenter.resume();
            }
            mPresenterHasView = true;
        }
    }

    public void onPause() {
        if (mPresenters != null && !mPresenters.isEmpty() && mPresenterHasView) {
            for (MvpPresenter presenter : mPresenters) {
                presenter.pause();
            }
            mPresenterHasView = false;
        }
    }

    public void onStop() {
        if (mPresenters != null && !mPresenters.isEmpty()) {
            for (MvpPresenter presenter : mPresenters) {
                presenter.stop();
            }
        }
    }

    public void onDestroy(boolean isFinal) {
        if (isFinal && mPresenters != null && !mPresenters.isEmpty()) {
            for (MvpPresenter presenter : mPresenters) {
                presenter.destroy();
            }
            mPresenters.clear();
            mPresenters = null;
        }
    }
}
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0x03 講在最後

該框架實現的Presenter恢復機制，儲存的id不止是單純的Presenter類名，大可不必擔心Presenter複用混亂的情況，具體可以看 PresenterStorage.java 的實現

此次說講Multi Presenter版本的Damon是新變支的2.0.0-alpha，未經過大量測試。 不過此前的Single Presenter版本的Damon，版本號1.1.0，則在開發環境穩定執行許久

最後再放上專案連結github.com/izyhang/Dam…

歡迎大家指出不足、留下您的意見~