问题
There are some similar answers, but not to this situation.
My situation is simple.
I have an Activity with two different layouts, one in Portrait, another in Landscape.
In Portrait, i use <FrameLayout> and add Fragment into it dynamically.
In Landscape, i use <fragment> so the Fragment is static. (in fact this doesn't matter)
It first starts in Portrait, then i added the Fragment by simply:
ListFrag listFrag = new ListFrag();
getSupportFragmentManager().beginTransaction()
.replace(R.id.FragmentContainer, listFrag).commit();
where ListFrag extends ListFragment.
Then i do a screen rotate. I found the listFrag is re-creating in the Landscape mode.
(In which i noticed the onCreate() method is called again with a non-null Bundle)
i tried to use setRetainInstance(false) like @NPike said in this post. But the getRetainInstance() is already false by default. It does not do what i expected as the docs said. Could anyone please explain?
The fragment i am dealing with, is a ListFragment, which does setListAdapter() in onCreate(). So the if (container == null) return null; method cannot be used here. (or i dont know how to apply).
I got some hints from this post. Should i use if (bundle != null) setListAdapter(null); else setListAdapter(new ...); in my ListFragment? But is there a nicer way to indeed removing/deleting the fragment when it is destroyed/detached, rather than doing it in its creation time? (so as the if (container == null) return null; method)
Edit:
The only neat way i found is doing getSupportFragmentManager().beginTransaction().remove(getSupportFragmentManager().findFragmentById(R.id.FragmentContainer)).commit(); in onSaveInstanceState(). But it will raise another problems.
When screen is partially obscured, like WhatsApp or TXT dialogue boxes pop up, the fragment will be disappeared also. (this is relatively minor, just visual issue)
When screen rotate, the Activity is completely destroyed and re-created. So i can re-add the fragment in
onCreate(Bundle)oronRestoreInstanceState(Bundle). But in the case of (1), as well as switching Activities, neitheronCreate(Bundle)noronRestoreInstanceState(Bundle)will be called when user get back to my Activity. I have nowhere to recreate the Activity (and retrieve data from Bundle).
Sorry I didn't say it clearly that, i already have a decision making, which the getSupportFragmentManager()...replace(...).commit(); line only run in Portrait mode.
Example code
I have extracted the simple code, for better illustration of the situration :)
MainActivity.java
package com.example.fragremovetrial;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
public class MainActivity extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (findViewById(R.id.FragmentContainer) != null) {
System.out.println("-- Portrait --"); // Portrait
ListFrag listFrag = new ListFrag();
getSupportFragmentManager().beginTransaction()
.replace(R.id.FragmentContainer, listFrag).commit();
} else {
System.out.println("-- Landscape --"); // Landscape
}
}
@Override
protected void onResume() {
super.onResume();
if (findViewById(R.id.FragmentContainer) != null) {
System.out.println("getRetainInstance = " +
getSupportFragmentManager().findFragmentById(R.id.FragmentContainer).getRetainInstance());
}
}
}
layout/activity_main.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/FragmentContainer"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />
layout-land/activity_main.xml (doesn't matter)
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
</LinearLayout>
ListFrag.java
package com.example.fragremovetrial;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.widget.ArrayAdapter;
public class ListFrag extends ListFragment {
private String[] MenuItems = { "Content A", "Contnet B" };
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
System.out.println("ListFrag.onCreate(): " + (savedInstanceState == null ? null : savedInstanceState));
setListAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, MenuItems));
}
}
Notice i got the following
Debug messages
-- Portrait --
ListFrag.onCreate(): null
getRetainInstance = false
(rotate Port -> Land)
ListFrag.onCreate(): Bundle[{android:view_state=android.util.SparseArray@4052dd28}]
-- Landscape --
Previously focused view reported id 16908298 during save, but can't be found during restore.
(rotate Land -> Port)
ListFrag.onCreate(): Bundle[{android:view_state=android.util.SparseArray@405166c8}]
-- Portrait --
ListFrag.onCreate(): null
getRetainInstance = false
(rotate Port -> Land)
ListFrag.onCreate(): Bundle[{android:view_state=android.util.SparseArray@4050fb40}]
-- Landscape --
Previously focused view reported id 16908298 during save, but can't be found during restore.
(rotate Land -> Port)
ListFrag.onCreate(): Bundle[{android:view_state=android.util.SparseArray@40528c60}]
-- Portrait --
ListFrag.onCreate(): null
getRetainInstance = false
where the number of Fragment created will not increase infinitely as screen keep rotating, which i cannot explain. (please help)
回答1:
The correct way to handle this is to put the following in your onCreate()
if (savedInstanceState == null) {
// Do fragment transaction.
}
回答2:
I finally come up with a solution to prevent unwanted Fragment re-creating upon the Activity re-creates. It is like what i mentioned in the question:
The only neat way i found is doing
getSupportFragmentManager().beginTransaction().remove(getSupportFragmentManager().findFragmentById(R.id.FragmentContainer)).commit();inonSaveInstanceState(). But it will raise another problems...
... with some improvements.
In onSaveInstanceState():
@Override
protected void onSaveInstanceState(Bundle outState) {
if (isPortrait2Landscape()) {
remove_fragments();
}
super.onSaveInstanceState(outState);
}
private boolean isPortrait2Landscape() {
return isDevicePortrait() && (getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE);
}
and the isDevicePortrait() would be like:
private boolean isDevicePortrait() {
return (findViewById(R.id.A_View_Only_In_Portrait) != null);
}
*Notice that we cannot use getResources().getConfiguration().orientation to determine if the device is currently literally Portrait. It is because the Resources object is changed RIGHT AFTER the screen rotates - EVEN BEFORE onSaveInstanceState() is called!!
If we do not want to use findViewById() to test orientation (for any reasons, and it's not so neat afterall), keep a global variable private int current_orientation; and initialise it by current_orientation = getResources().getConfiguration().orientation; in onCreate(). This seems neater. But we should be aware not to change it anywhere during the Activity lifecycle.
*Be sure we remove_fragments() before super.onSaveInstanceState().
(Because in my case, i remove the Fragments from the Layout, and from the Activity. If it is after super.onSaveInstanceState(), the Layout will already be saved into the Bundle. Then the Fragments will also be re-created after the Activity re-creates. ###)
### I have proved this phenomenon. But the reason of What to determine a Fragment restore upon Activity re-create? is just by my guess. If you have any ideas about it, please answer my another question.
回答3:
In your onCreate() method you should only create your ListFrag if you are in portrait mode. You can do that by checking if the FrameLayout view that you only have in the portrait layout is not null.
if (findViewById(R.id.yourFrameLayout) != null) {
// you are in portrait mode
ListFrag listFrag = new ListFrag();
getSupportFragmentManager().beginTransaction()
.replace(R.id.FragmentContainer, listFrag).commit();
} else {
// you are in landscape mode
// get your Fragment from the xml
}
In the end if you switch from portrait to landscape layout, you don't want to have another ListFrag created, but use the Fragment you have specified in your xml.
回答4:
@midnite ,first of all thanks for your question, I had the same question, on wich I worked for days. Now I wound some tricky resolution to this problem - and want to share this to community. But If someone has better solution, please write in comments.
So, I have same situation - different layouts for two device orientation. In portrait there is no need for DetailsFragment.
I simply in OnCreate trying to find already created fragments:
fragment = (ToDoListFragment) getFragmentManager().findFragmentByTag(LISTFRAGMENT);
frameDetailsFragment = (FrameLayout) findViewById(R.id.detailsFragment);
detailsFragment = (DetailsFragment) getFragmentManager().findFragmentByTag(DETAILS_FRAGMENT);
settingsFragment = (SettingsFragment) getFragmentManager().findFragmentByTag(SETTINGS_FRAGMENT);
Right after that I am adding my main fragment -
if (fragment == null){
fragment = new ToDoListFragment();
getFragmentManager().beginTransaction()
.add(R.id.container, fragment, LISTFRAGMENT)
.commit();
}
And clear back stask of my fragments:
if (getFragmentManager().getBackStackEntryCount() > 0 ) {
getFragmentManager().popBackStackImmediate();
}
And the MOST interesting is here -
destroyTmpFragments();
Here is the method itself:
private void destroyTmpFragments(){
if (detailsFragment != null && !detailsFragment.isVisible()) {
Log.d("ANT", "detailsFragment != null, Destroying");
getFragmentManager().beginTransaction()
.remove(detailsFragment)
.commit();
detailsFragment = null;
}
if (settingsFragment != null && !settingsFragment.isVisible()) {
Log.d("ANT", "settingsFragment != null, Destroying");
getFragmentManager().beginTransaction()
.remove(settingsFragment)
.commit();
settingsFragment = null;
}
}
As you can see, I clean manually all fragments, that FragmentManager gentfully saved for me (great thanks to him). In log I have next lifecycle calls:
04-24 23:03:27.164 3204 3204 D ANT MainActivity onCreate()
04-24 23:03:27.184 3204 3204 I ANT DetailsFragment :: onCreateView
04-24 23:03:27.204 3204 3204 I ANT DetailsFragment :: onActivityCreated
04-24 23:03:27.204 3204 3204 I ANT DetailsFragment :: onDestroy
04-24 23:03:27.208 3204 3204 I ANT DetailsFragment :: onDetach
So in onActivityCreated make your views check for null - in case fragment is not visible. It will be deleted little bit later (It is so maybe cuz fragment manager's remove is async) After, in activity's code we can create brand new Fragment instance, with proper layout (fargmnet's placeholder) and fragment will be able to find it's views for example, and will not produce NullPointerException
But, fragments that are in back stack are deleted pretty fast, without call to onActivityCreated (with th help of above code:
if (getFragmentManager().getBackStackEntryCount() > 0 ) {
getFragmentManager().popBackStackImmediate();
}
At last, at the end i add fragment if I am in land orientation -
if (frameDetailsFragment != null){
Log.i("ANT", "frameDetailsFragment != null");
if (EntryPool.getPool().getEntries().size() > 0) {
if (detailsFragment == null) {
detailsFragment = DetailsFragment.newInstance(EntryPool.getPool().getEntries().get(0), 0);
}
getFragmentManager().beginTransaction()
.replace(R.id.detailsFragment, detailsFragment, DETAILS_FRAGMENT)
.commit();
}
}
来源：https://stackoverflow.com/questions/15496362/handle-fragment-duplication-on-screen-rotate-with-sample-code