MVP 和 RxJava - 在 Android 上处理方向变化

Question

我正在使用类似于 google-samples 存储库的 MVP 和 RxJava。

我想问一下如何正确处理屏幕方向变化。

Answer 1

我是在presenter中将视图的状态封装在特定的ViewStateclass中处理的，测试起来很方便。

public interface BaseViewState {
    void saveState(@NonNull Bundle outState);

    void restoreState(@Nullable Bundle savedInstanceState);
}

class HomeViewState implements BaseViewState {

    static final long NONE_NUM = -1;

    static final String STATE_COMIC_NUM = "state_comic_num";

    private long comicNum = NONE_NUM;

    @Inject
    HomeViewState() {
    }

    @Override
    public void saveState(@NonNull Bundle outState) {
        outState.putLong(STATE_COMIC_NUM, comicNum);
    }

    @Override
    public void restoreState(@Nullable Bundle savedInstanceState) {
        if (savedInstanceState != null) {
            comicNum = savedInstanceState.getLong(STATE_COMIC_NUM, NONE_NUM);
        }
    }

    long getComicNumber() {
        return comicNum;
    }

    void setComicNum(long comicNum) {
        this.comicNum = comicNum;
    }
}

get/set 来自 presenter 中 viewState 的值，这有助于保持更新，以及 presenter 无状态。

public class HomePresenter implements HomeContract.Presenter {

    private HomeViewState viewState;

    HomeViewState getViewState() {
        return viewState;
    }

    @Override
    public void loadComic() {
       loadComic(viewState.getComicNumber());
    }
    ...
}

在 Activity 中，因为视图应启动保存和恢复调用。

public class MainActivity extends BaseActivity implements HomeContract.View {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            ...
            homePresenter.getViewState().restoreState(savedInstanceState);
        }


        @Override
        public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
            super.onSaveInstanceState(outState, outPersistentState);

            homePresenter.getViewState().saveState(outState);
        }
     ...
}

Answer 2

还有另一种策略可以保存演示者状态以及 Observable 的状态：retain Fragment。这样你就省略了将数据保存到 Bundle 中的标准 Android 方法（它只允许保存简单变量而不是网络请求的状态。）

Activity:

public class MainActivity extends AppCompatActivity implements MainActivityView {
    private static final String TAG_RETAIN_FRAGMENT = "retain_fragment";

    MainActivityPresenter mPresenter;

    private MainActivityRetainFragment mRetainFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        initRetainFragment();
        initPresenter();
    }

    private void initRetainFragment() {
        FragmentManager fm = getSupportFragmentManager();
        mRetainFragment = (MainActivityRetainFragment) fm.findFragmentByTag(TAG_RETAIN_FRAGMENT);
        if (mRetainFragment == null) {
            mRetainFragment = new MainActivityRetainFragment();
            fm.beginTransaction().add(mRetainFragment, TAG_RETAIN_FRAGMENT).commit();
        }
    }

    private void initPresenter() {
        mPresenter = mRetainFragment.getPresenter();
        mRetainFragment.retainPresenter(null);
        if (mPresenter == null) {
            mPresenter = new MainActivityPresenter();
        }
        mPresenter.attachView(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (!isFinishing()) {
            mRetainFragment.retainPresenter(mPresenter);
            return;
        }
        mPresenter.detachView();
        mPresenter = null;
    }
}

保留Fragment:

public class MainActivityRetainFragment extends Fragment {
    private MainActivityPresenter presenter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRetainInstance(true);
    }

    public void retainPresenter(MainActivityPresenter presenter) {
        this.presenter = presenter;
    }

    public MainActivityPresenter getPresenter() {
        return presenter;
    }
}

注意 activity 生命周期事件的处理方式。创建 Activity 时，将保留 Fragment 添加到后台堆栈，并在生命周期事件中从后台堆栈恢复。 retain Fragment 没有任何视图，它只是配置更改期间演示者的持有者。注意主要的调用，它可以从 backstack 中恢复完全相同的片段（及其内容）：

setRetainInstance(true)

如果您担心内存泄漏：每次恢复演示者时都会恢复演示者的视图：

mPresenter.attachView(this);

所以之前的 Activity 引用被新的替换了。

这里有更多关于这种配置更改处理的信息here

MVP 和 RxJava - 在 Android 上处理方向变化

MVP and RxJava - Handling Orientation Changes on Android

android

screen-orientation

rx-java

rx-android