我有3个片段(片段主页,片段A,片段B和片段C)。首次运行应用程序将显示Fragment Home(设置为Mainactivity)。从导航绘图项可以选择每个片段。每个选定的项目都将显示细节片段。
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Fragment A)时会显示片段A的页面。但是当我旋转设备时,为什么我的片段会回到片段主页并且不会停留在当前片段?如何处理它?<br/>
(2)。在片段B中,我在GridView中显示图像。但是当我旋转设备时,为什么我的片段会回到Fragment Home并且不会停留在当前片段?如何处理它并仍然用现有数据显示这个片段?
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);
}
答案 0 :(得分:1)
解决了这个问题。在MainActivity中添加以下内容:
id
在每个片段中添加条件以检查savedInstanceState是否为空。
谢谢大家
答案 1 :(得分:0)
您需要覆盖片段A和B中的onConfigurationChanged(Configuration newConfig)
方法,告诉他们在应用配置更改时留在那里。例如:
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
// get current fragment
Fragment fragment = mAdapter.getItem(currentItem);
if(fragment!=null){
fragment.onResume();
}
}
答案 2 :(得分:0)
因为每次旋转屏幕都会调用onCreate()方法。
解决
onCreate()方法中的检查 savedInstanceState()是否为空
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(null == savedInstanceState){
//set you initial fragment object
}
else
{
//Load the fragment by tag
}
}
并在所有片段中的onPause()之前保存实例状态
@Override
protected void onSaveInstanceState(Bundle bundle1)
{
super.onSaveInstanceState(bundle1); Log.i(tag,"inside onSaveInstanceState");
bundle1.putInt("tag",n);
}