如何处理屏幕旋转并在Fragment中保存数据? [英] How to handle rotate screen and save data in Fragment?

问题描述

我有3个片段(片段首页，片段A，片段B和片段C).首次运行应用程序时将显示"Fragment Home"(在主活动"中设置).从导航绘图项目可以选择每个片段.每个选定的项目都会显示详细的片段.

I have 3 Fragment (Fragment Home, Fragment A, Fragment B and Fragment C). First time app run will display Fragment Home (Set in Mainactivity). From Navigation Draw Item can choose every fragment. Every selected item will display detail Fragment.

我在处理数据和保留片段时遇到问题:

(1).当我选择一个片段(例如Fragment A)时，将显示Fragment A的页面.但是，当我旋转设备时，为什么我的片段回到Fragment Home而不停留在当前的Fragment上?如何处理?

(2).在片段B中，我在GridView中显示图像.但是，当我旋转设备时，为什么我的片段返回到Fragment Home而不停留在当前的Fragment上?如何处理它并仍然使用现有数据显示该片段?

I have problems to handle data and retain fragment :

(1). When I select a fragment (for example Fragment A) will show the page of Fragment A. But when I rotate the device, why my fragment back to Fragment Home and not stay at current Fragment ??How to handle it ?

(2). In Fragment B, I show image in GridView. But when I rotate the device, why my fragment back to Fragment Home and not stay at current Fragment ??How to handle it and still display this fragment with existing Data?

这是我的代码:

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

private static final String LOG_TAG = MainActivity.class.getSimpleName();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
        this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    displaySelectedItem(R.id.nav_home);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    displaySelectedItem(item.getItemId());

    return true;
}

private void displaySelectedItem (int itemId) {
    Fragment fragment = null;

    switch (itemId){
        case R.id.nav_home:
            fragment = new FragmentHome();
            break;
        case R.id.nav_a:
            fragment = new FragmentA();
            break;
        case R.id.nav_b:
            fragment = new FragmentB();
            break;
        case R.id.nav_c:
            fragment = new FragmentC();
            break;
        case R.id.nav_d:
            fragment = new FragmentD();
            break;
    }

    FragmentManager fragmentManager = MainActivity.this.getSupportFragmentManager();
    List<Fragment> fragments = fragmentManager.getFragments();
    if (fragments != null) {
        for(Fragment f : fragments){
            fragmentManager.popBackStack();

        }
    }


    //replace the fragment
    if (fragment != null) {
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.content_frame, fragment, "TAG_FRAGMENT");
        fragmentTransaction.commit();
    }

    DrawerLayout drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawerLayout.closeDrawer(GravityCompat.START);
}

片段A:

public class FragmentA extends Fragment {
public FragmentA() {
    super();
}

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

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_a, container, false);
    return rootView;
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    getActivity().setTitle("Fragment A");
}
}

片段B:

public class FragmentB extends Fragment {
private static final String LOG_TAG = FragmentB.class.getSimpleName();

private ImageAdapter imageAdapter;
private ArrayList<Movie> movieList;

public FragmentNowPlaying() {
    super();
}

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

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_b, container, false);
    GridView gridView = (GridView) rootView.findViewById(R.id.gridviewNowPlaying);

    imageAdapter = new ImageAdapter(getContext(), R.layout.fragment_b, movieList);
    if (savedInstanceState == null) {
        movieList = new ArrayList<Movie>();
    }else{
        movieList = (ArrayList<Movie>) savedInstanceState.get("MovieList");
    }

    gridView.setAdapter(imageAdapter);
    return rootView;
}

@Override
public void onSaveInstanceState(Bundle outState) {
    outState.putParcelableArrayList("MovieList",movieList);
    super.onSaveInstanceState(outState);
}

推荐答案

解决了此问题.在MainActivity中添加以下内容:

Solved this issue. In MainActivity add this :

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt(STATE_SELECTED_POSITION, mCurrentSelectedPosition);
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    mCurrentSelectedPosition = savedInstanceState.getInt(STATE_SELECTED_POSITION, 0);
    Menu menu = navigationView.getMenu();
    menu.getItem(mCurrentSelectedPosition).setChecked(true);
}

在每个片段中添加条件以检查savedInstanceState是否为空.

In every fragment add condition to check savedInstanceState null or not.

谢谢大家

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