Android 如何处理旋转屏幕并将数据保存在片段中？

我有3个片段（片段Home、片段A、片段B和片段C）。应用程序首次运行时将显示片段主页（在Mainactivity中设置）。从导航绘图项可以选择每个片段。每个选定项目都将显示详细信息片段

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（例如片段a）时，将显示片段a的页面。但是当我旋转设备时，为什么我的片段返回到片段主页而不是停留在当前片段？如何处理它？

(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片段主页而不是停留在当前片段？如何处理它并仍然使用现有数据显示此片段？

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);
}

公共类FragmentB扩展了Fragment{
私有静态最终字符串LOG_TAG=FragmentB.class.getSimpleName（）；
专用图像适配器；
私人电影导演；
公共碎片{
超级（）；
}
@凌驾
创建时的公共void（@Nullable Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setRetainInstance（真）；
}
@可空
@凌驾
创建视图时的公共视图（LayoutFlater充气机、@Nullable ViewGroup容器、@Nullable Bundle savedInstanceState）{
视图根视图=充气机。充气（R.layout.fragment_b，容器，false）；
GridView GridView=（GridView）rootView.findViewById（R.id.gridviewNowPlaying）；
imageAdapter=新的imageAdapter（getContext（），R.layout.fragment_b，movieList）；
如果（savedInstanceState==null）{
movieList=newarraylist（）；
}否则{
movieList=（ArrayList）savedInstanceState.get（“movieList”）；
}
setAdapter（imageAdapter）；
返回rootView；
}
@凌驾
SaveInstanceState上的公共无效（束超出状态）{
杰出的电影艺术家（MovieList，MovieList）；
super.onSaveInstanceState（超出状态）；
}

您需要覆盖片段A和B中的

OnConfiguration Changed（Configuration newConfig）

方法，以便在应用程序配置更改时告诉它们留在那里。例如：

      @Override
        public void onConfigurationChanged(Configuration newConfig) {
                super.onConfigurationChanged(newConfig);
                // get current fragment
                Fragment fragment = mAdapter.getItem(currentItem);
                if(fragment!=null){
                     fragment.onResume();
                }
        }

---

因为每次旋转屏幕时都会调用onCreate（）方法

解决问题

在onCreate（）方法中，检查savedInstanceState（）是否为null

@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if(null == savedInstanceState){
             //set you initial fragment object 
        }
    else
        {
        //Load the fragment by tag
        }
  }

并在所有片段中保存onPause（）之前的实例状态

@Override 
protected void onSaveInstanceState(Bundle bundle1)
{ 
super.onSaveInstanceState(bundle1); Log.i(tag,"inside onSaveInstanceState");      
bundle1.putInt("tag",n); 

}

---

已解决此问题。在MainActivity中添加以下内容：

@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null

---

谢谢大家

尝试在片段中设置

setRetainInstance（true）

@emdadhosain已经尝试了，但仍然无法。您能举一些例子吗？

@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);
}