Develop Reference

how to save android recycler view state (scroll position) in an activity with two fragments

I am new to Android and, as a first step, am building an app, for running in a handset, with an activity in which I put two fragments. The first fragment has a recycler view of items that are supposed to represent article titles. When I click on one, the second fragment opens and shows the title (in a text view) and the content (in another text view) of the article (for the moment, for simplicity, I put the article title as fake titles and I have a setting for which the content is not shown but it is shown the title in the content text view too).
I want to save the scroll position of the recycler view.
When I scroll down, having on top of the screen an article title different from the first, I choose an article and my second fragment opens with the expected contents, and that's ok. When I rotate to landscape, the same fragment contains the same content, ok. So:
1) when I press the back button from the landscape, returning to the first fragment, I get the same setting for the recycler view, ok;
2) when I rotate again to portrait, remaining on the second fragment, it is ok too. Now, if I press the back button to return to the first fragment, to the list of articles, the recycler view is NOT set to start with the item I initially scrolled to. What can I do?
I have this code in the first fragment, the one containing the recycler view:
#Override
public void onSaveInstanceState(Bundle state) {
int lastFirstVisiblePosition = ((LinearLayoutManager) recyclerView.getLayoutManager()).findFirstCompletelyVisibleItemPosition();
state.putInt(Articles.RECYCLER_POSITION_KEY, lastFirstVisiblePosition);
super.onSaveInstanceState(state);
}
#Override
public void onActivityCreated(Bundle state) {
super.onActivityCreated(state);
if (state != null) {
int lastFirstVisiblePosition = state.getInt(Articles.RECYCLER_POSITION_KEY);
((LinearLayoutManager) recyclerView.getLayoutManager()).scrollToPosition(lastFirstVisiblePosition);
}
}
What am I missing? Thanks.
[EDIT] In my listener is this, for invoking the second fragment:
ArticleReaderFrag newFragment = new ArticleReaderFrag();
Bundle args = new Bundle();
args.putString(NEW_FRAG_TITLE_KEY, item);
args.putString(NEW_FRAG_BODY_KEY, itemb);
newFragment.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.main_activity, newFragment);
transaction.addToBackStack(null);
transaction.commit();

Reuse Fragment
When the Activity launches for the first time create a new instance of Fragment and use a TAG to save it with FragmentManager. When the activity gets recreated after orientation change. Retreive the old instance using the Tag.
Here is a sample code which you should have in your activity.
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.first_activity);
fragmentManager = getSupportFragmentManager();
if(savedInstanceState==null) {
userFragment = UserNameFragment.newInstance();
fragmentManager.beginTransaction().add(R.id.profile, userFragment, "TAG").commit();
}
else {
userFragment = fragmentManager.findFragmentByTag("TAG");
}
}
How to save scroll position?
That happens by default. Read this answer for more detail.
EDIT
I believe this is your method
public createSecondFragment(int position){
ArticleReaderFrag newFragment = new ArticleReaderFrag();
Bundle args = new Bundle();
args.putString(NEW_FRAG_TITLE_KEY, item);
args.putString(NEW_FRAG_BODY_KEY, itemb);
newFragment.setArguments(args);
FragmentTransaction transaction =
getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.main_activity, newFragment);
transaction.addToBackStack(null);
transaction.commit();
}
Save the position of on rotation and use that position to load the specific fragment.
Call the method when the activity is recreated after orientation change
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.first_activity);
if(savedInstanceState!=null) {
int lastSavedPosition = // Your logic
createSecondFragment(lastSavedPosition )
}
}

Android fragments using v7 appCompat library

I downloaded the fragmentbasics.zip from the Android Training site. At the bottom of the page (from provided link) there is a section stating "If you're using the v7 appcompat library, your activity should instead extend ActionBarActivity, which is a subclass of FragmentActivity". I am using the android-support-v7-appcompat.jar in my project.
I did as the tutorial page says and updated 'MainActivity.java' to extend ActionBarActivity instead of FragmentActivity, I am now getting the below errors...
The hierarchy of the type MainActivity is inconsistent
The type android.support.v4.app.TaskStackBuilder$SupportParentable cannot be resolved. It is indirectly referenced from required .class files
MainActivity.java
public class MainActivity extends ActionBarActivity
implements HeadlinesFragment.OnHeadlineSelectedListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.news_articles);
// Check whether the activity is using the layout version with
// the fragment_container FrameLayout. If so, we must add the first fragment
if (findViewById(R.id.fragment_container) != null) {
// However, if we're being restored from a previous state,
// then we don't need to do anything and should return or else
// we could end up with overlapping fragments.
if (savedInstanceState != null) {
return;
}
// Create an instance of ExampleFragment
HeadlinesFragment firstFragment = new HeadlinesFragment();
// In case this activity was started with special instructions from an Intent,
// pass the Intent's extras to the fragment as arguments
firstFragment.setArguments(getIntent().getExtras());
// Add the fragment to the 'fragment_container' FrameLayout
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, firstFragment).commit();
}
}
public void onArticleSelected(int position) {
// The user selected the headline of an article from the HeadlinesFragment
// Capture the article fragment from the activity layout
ArticleFragment articleFrag = (ArticleFragment)
getSupportFragmentManager().findFragmentById(R.id.article_fragment);
if (articleFrag != null) {
// If article frag is available, we're in two-pane layout...
// Call a method in the ArticleFragment to update its content
articleFrag.updateArticleView(position);
} else {
// If the frag is not available, we're in the one-pane layout and must swap frags...
// Create fragment and give it an argument for the selected article
ArticleFragment newFragment = new ArticleFragment();
Bundle args = new Bundle();
args.putInt(ArticleFragment.ARG_POSITION, position);
newFragment.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
}
}
}
Based on the tutorial I guess I am doing things correctly, any ideas why I would be getting these errors?
Steps to reproduce:
download the sample from provided link (top of post)
right click project -> build path -> add external arhchives
find your v7 appCompat support jar and click open
observe errors

Try to update the android.support.v4

Get data result from second Fragment

In my MainActivity extends FragmentActivity, I have a FragmentA, When I press a Button in FragmentA, I call to FragmentB.
FragmentB f = FragmentB.newInstance(1);
getSupportFragmentManager().beginTransaction().replace(R.id.llMain, f).addToBackStack(null).commit();
In FragmentB, I create a Object People p1(with Name and age) . And When I press a Button B in FragmentB, I call
getFragmentManager().popBackStack();
It will return FragmentA,
So, I want to pass data Object People p1 from FragmentB to FragmentA. What do i have to do?
I try to search but can't find a solution.

create CallBack in your Fragment and handle it in FragmentActivity,
google example has this realization
declaring OnHeadlineSelectedListener callback
public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;
// The container Activity must implement this interface so the frag can deliver messages
public interface OnHeadlineSelectedListener {
/** Called by HeadlinesFragment when a list item is selected */
public void onArticleSelected(int position);
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// We need to use a different list item layout for devices older than Honeycomb
int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?
android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1;
// Create an array adapter for the list view, using the Ipsum headlines array
setListAdapter(new ArrayAdapter<String>(getActivity(), layout, Ipsum.Headlines));
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception.
try {
mCallback = (OnHeadlineSelectedListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnHeadlineSelectedListener");
}
}
#Override
public void onListItemClick(ListView l, View v, int position, long id) {
// Notify the parent activity of selected item
mCallback.onArticleSelected(position);
// Set the item as checked to be highlighted when in two-pane layout
getListView().setItemChecked(position, true);
}
Realize callback method in FragmentActivity and send (by .setArguments()) data from HeadLinesFragment to ArticleFragment, if ArticleFragment is available
public class MainActivity extends FragmentActivity
implements HeadlinesFragment.OnHeadlineSelectedListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.news_articles);
// Check whether the activity is using the layout version with
// the fragment_container FrameLayout. If so, we must add the first fragment
if (findViewById(R.id.fragment_container) != null) {
// However, if we're being restored from a previous state,
// then we don't need to do anything and should return or else
// we could end up with overlapping fragments.
if (savedInstanceState != null) {
return;
}
// Create an instance of ExampleFragment
HeadlinesFragment firstFragment = new HeadlinesFragment();
// In case this activity was started with special instructions from an Intent,
// pass the Intent's extras to the fragment as arguments
firstFragment.setArguments(getIntent().getExtras());
// Add the fragment to the 'fragment_container' FrameLayout
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, firstFragment).commit();
}
}
public void onArticleSelected(int position) {
// The user selected the headline of an article from the HeadlinesFragment
// Capture the article fragment from the activity layout
ArticleFragment articleFrag = (ArticleFragment)
getSupportFragmentManager().findFragmentById(R.id.article_fragment);
if (articleFrag != null) {
// If article frag is available, we're in two-pane layout...
// Call a method in the ArticleFragment to update its content
articleFrag.updateArticleView(position);
} else {
// If the frag is not available, we're in the one-pane layout and must swap frags...
// Create fragment and give it an argument for the selected article
ArticleFragment newFragment = new ArticleFragment();
Bundle args = new Bundle();
args.putInt(ArticleFragment.ARG_POSITION, position);
newFragment.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
}
}

You should use an interface within Activity for communication between fragments. Check this android training lesson.
All Fragment-to-Fragment communication is done through the associated
Activity. Two Fragments should never communicate directly.
You can pass arguments to a Fragment with Bundle. Change your code to:
FragmentB f = FragmentB.newInstance(1);
Bundle args = new Bundle();
args.putString("NAME", name);
args.putInt("AGE", age);
f.setArguments(args);
getSupportFragmentManager().beginTransaction().replace(R.id.llMain, f).addToBackStack(null).commit();
and then retrieve the arguments for example in FragmentA's onCreateView with:
int age = getArguments().getInt("AGE");
//or with a second parameter as the default value
int age = getArguments().getInt("AGE", 0);
If you want to pass the whole People object to the Bundle, you need to make the class serializable. I think it's easier to pass the variables and then recreate the object.

All fragments visible after rotation

i have a problem with fragments when my device is rotate:
i have 5 fragments:
Menu is the first fragment, when activity start, it is launched.
AddUser (simple fragment that i can see when i press a button in menu fragment)
DetailApp (simple fragment that i can see when i press a button in menu fragment)
DetailUser (simple fragment that i can see when i press a button in menu fragment)
ListUser (ListFragment that i can see when i press a button in menu fragment)
When i start my activity in vertical mode, i can see correctly my fragments, when i rotate my smartphone, i can see.. all fragments overlapping!
if i launch ListUser i have:
IllegalArgumentException: No view found for id 0x... for fragment ...
when start my Menu fragments:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_manager);
this is oncreate
// Check whether the activity is using the layout version with
// the fragment_container FrameLayout. If so, we must add the first fragment
if (findViewById(R.id.fragment_container) != null) {
// However, if we're being restored from a previous state,
// then we don't need to do anything and should return or else
// we could end up with overlapping fragments.
if (savedInstanceState != null) {
return;
}
//first frame show a menu
Menu firstFragment = new Menu();
// In case this activity was started with special instructions from an Intent,
// pass the Intent's extras to the fragment as arguments
firstFragment.setArguments(getIntent().getExtras());
// Add the fragment to the 'fragment_container' FrameLayout
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, firstFragment).commit();
}
fragment container at start is void..
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
when i press a button and one of fragments start:
#Override
public void onDetailApp(int position) {
// The user selected the headline of an article from the HeadlinesFragment
// Capture the article fragment from the activity layout
DetailApp appFrag = (DetailApp)
getSupportFragmentManager().findFragmentById(R.id.detailapp_fragment);
if (appFrag != null) {
// If article frag is available, we're in two-pane layout...
// Call a method in the ArticleFragment to update its content
appFrag.updateAppointmentView(position);
} else {
// If the frag is not available, we're in the one-pane layout and must swap frags...
// Create fragment and give it an argument for the selected article
DetailApp newFragment = new DetailApp();
Bundle args = new Bundle();
args.putInt(DetailApp.ARG_APPOINTMENT, position);
newFragment.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
}
}
this is onCreateView from DetailUser, AddUser, DetailApp:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// If activity recreated (such as from screen rotate), restore
// the previous article selection set by onSaveInstanceState().
// This is primarily necessary when in the two-pane layout.
if (savedInstanceState != null) {
mCurrentPosition = savedInstanceState.getInt(ARG_POSITION);
}
// Inflate the layout for this fragment
return inflater.inflate(R.layout.detail_adduser, container, false);
}
Who can help me?

replace
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, firstFragment).commit();
by
getSupportFragmentManager().beginTransaction()
.replace(R.id.fragment_container, firstFragment).commit();
99% of times it solves duplication issues.

i add this on my Manifest activity and override onConfigurationChanged:
android:configChanges="keyboardHidden|orientation|screenSize"
<activity
android:name="com.map.manager.ManagerActivity"
android:configChanges="keyboardHidden|orientation|screenSize"
android:label="#string/title_activity_manager" >
</activity>
and i have no more problems! i can see correctly layout vertical and horizontal (when i rotate the smartphone).
but i found this: why-not-use-always-androidconfigchanges
must i put in "blacklist" all possible configuration change? locale touchscreen screenSize etc?

Android fragment - different layout into fragment

I'm trying to develop an application compatible with smartphones (one pane layout) and tablets (two panes layout). My app is displayed as shown below:
(source: android10.org)
I used the example available in Google developers website.
The example works fine. But for my app, I need to use different layout in the WebView fragment. Each element selected in ListView fragment shows a specific layout into the right fragment.
This is my code called when an element is clicked :
public void onArticleSelected(int position) {
// The user selected the headline of an article from the
// HeadlinesFragment
// Capture the article fragment from the activity layout
BodyFragment articleFrag = (BodyFragment) getSupportFragmentManager().findFragmentById(R.id.body_fragment);
if (articleFrag != null) {
// If article frag is available, we're in two-pane layout...
// Call a method in the ArticleFragment to update its content
articleFrag.updateArticleView(position);
} else {
// If the frag is not available, we're in the one-pane layout and
// must swap frags...
// Create fragment and give it an argument for the selected
// article
BodyFragment newFragment = new BodyFragment();
Bundle args = new Bundle();
args.putInt(BodyFragment.ARG_POSITION, position);
newFragment.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this
// fragment,
// and add the transaction to the back stack so the user can
// navigate back
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
}
}
How can I should make it? I thought to replace dynamically the layout into the fragment, but it is not possible.
Is anybody has a solution?
thanks in advance