I have two fragments FragmentA and FragmentB.
From Fragment A i update Views in Fragment B by passing custom object as a parameter to a method in Fragment B.
For example below is the Fragment B:
public class FragmentB extends Fragment {
private ArrayList<String> customObj = new ArrayList<String>();
public void updateViews(ArrayList<String> obj) {
customObj = obj;
}
#Override
public void onSaveInstanceState(Bundle outState) {
System.out.println("Custom Object : "+customObj);//custom object is always empty
}
Now, whenever i rotate the screen, the custom object is al;ways empty.
Note
Here I am just updating the views of Fragement B. The object is passed as a parameter from Fragment A to the method updateViews of Fragment B.
Also, i am not looking forward to define static for custom object.
You can do two things
1. Store that custom object somewhere which is not created every time orientation is changed i.e. Application class, Service etc.
2. Store that object inside the Bundle which you get as a parameter inside OnSaveInstanceState() and use that Bundle to set the Object in OnRestoreInstanceState() or OnCreate()...
For Example,
#Override
protected void onCreate(Bundle savedInstanceState) {
Logger.d("Dash onCreate");
super.onCreate(savedInstanceState);
...
// create fragments to use
if (savedInstanceState != null) {
//get your Object
}
if (yourObject != null)
//restore the View using yourObject
...
}
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
}
Now in your Custom Class you will have to either implement Serializable or Parcelable for storing that inside a Bundle. Serialization is simple but if you implement Parcellable you have more control on it.
Some other similar threads on SO related to this topic are
Similar Example
Another good example
You can get a similar Example in Android Documentations for Fragments.
Related
When my activity containing viewpager is killed by system in background and then restores its state, fragments are correctly created and viewpager adapter can also point to them correctly.
But when I get a fragment reference and try to access its fields, they are all null (checked by using breakpoint).
I checked this by placing breakpoints in fragment onCreateView() and in my activity button's clickListener.
((WelcomeFragment)homeActivityFragmentPageAdapter.getItem(POSITION_HOME)).setdata(myData);
Now this method will through null pointer exception since setdata(data) is internally accessing arraylist field of fragment.
This creates a problem for me since, my activity has to continuously feed network data to the fragment by calling its public method (as suggested by documentation).
How to insure that after state restored; correct instance is pointed in my activity.
Try to use instantiateItem adapter method instead getItem.
((WelcomeFragment)homeActivityFragmentPageAdapter.instantiateItem(mViewPager, POSITION_HOME)).setdata(myData);
Method getItem is overrided method, and common use is creation of child fragments.
EDIT:
In case of the question's scenario, you also need to store the state of FragmentStatePagerAdapter manually:
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
savedInstanceState
.putParcelable("pages",homeActivityFragmentPageAdapter.saveState());
super.onSaveInstanceState(savedInstanceState);
}
Then you can retrieve the state in oncreate:
#Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState != null) {
homeActivityFragmentPageAdapter.restoreState(savedInstanceState.getParcelable("pages"),this.getClassLoader());
welcomeFragment = (WelcomeFragment) homeActivityFragmentPageAdapter.instantiateItem(mViewPager, POSITION_HOME);
}
else { //simply create a new instance here}
homeActivityFragmentPageAdapter.addFragmentToAdapter(welcomeFragment);
homeActivityFragmentPageAdapter.notifyDataSetChanged();
}
I know this question is very common and I have read so many different answers but none fits in my problem. In my application, I have an activity and in rhye activity I load a fragment. I also send some data(in the form of Bundle) to the fragment. So my Problem is when the screen is rotated, I save the fragment in onSaveInstanceState Activity method and check in onCreate Method weather savedInstance is null or not and on that basis I load the fragment.
Activity code :
#Override
public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
super.onSaveInstanceState(outState, outPersistentState);
outState.putParcelable(Const.TAG_REQ_CUSTOM,DetailsItems);
outState.putString(Const.TAG_FLOW, Const.TAG_MAIN_FLOW);
getSupportFragmentManager().putFragment(outState,"current_fragment",fragment);
}
onCreate Method :
if (findViewById(R.id.fragment_frame) != null) {
if (savedInstanceState != null) {
// this invoke when screen rotate but the app crash
DetailsItems = savedInstanceState.getParcelable(Const.TAG_REQ_CUSTOM);
String flow = savedInstanceState.getString(Const.TAG_FLOW);
ft = getSupportFragmentManager().getFragment(savedInstanceState,"current_fragment");
mFragmentManager=getSupportFragmentManager();
mFragmentTransaction = mFragmentManager.beginTransaction();
bundle= new Bundle();
bundle.putString(Const.TAG_FLOW, flow);
bundle.putParcelable(Const.TAG_REQ_BOOKING_DETAILS, bookingDetailsItems);
ft.setArguments(bundle);
mFragmentTransaction.replace(R.id.fragment_frame, ft).commit();
}else{
// load fragment on first time
}
}
So my Question is: Where do I have to save the custom Object(in parent Activity or in fragment) ?
When my saved Instance is not null than app crashesh and logs is :
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
You should use ViewModel. ViewModel is specifically made for this purpose.
From the docs:
ViewModel is a class that is responsible for preparing and managing the data for an Activity or a Fragment. It also handles the communication of the Activity / Fragment with the rest of the application (e.g. calling the business logic classes).
use this code in Activity :
if (findViewById(R.id.fragment_frame) != null) {
if (savedInstanceState != null) {
fragment =getSupportFragmentManager().getFragment(savedInstanceState,"current_fragment");
}else{
// load fragment on first time
}
}
and in fragment :
//save custom object
#Override
public void onSaveInstanceState(Bundle outState){
super.onSaveInstanceState(outState);
outState.putParcelable("key",customObject);
}
//now retrieve here
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
if (savedInstanceState != null)
customObject= savedInstanceState.getParcelable("key");
}
Take a look at onRetainNonConfigurationInstance() and getLastNonConfigurationInstance()
From docs:
Called by the system, as part of destroying an activity due to a configuration change, when it is known that a new instance will immediately be created for the new configuration. You can return any object you like here, including the activity instance itself, which can later be retrieved by calling getLastNonConfigurationInstance() in the new activity instance.
I have two activities says Activity A and Activity B.
Activity A contains Fragments AF1,AF2.
Activity B contains Fragments BF1,BF2.
Currently I am in AF1.
How can we pass data(bundle) from AF1 to AF2?
How can we pass data (bundle) from AF1 to BF2?
The first approach is to use interfaces. Here is a breakdown of the steps:
Create an interface in your AF1 fragment - a method in that interface will be called and the data passed back through the arguments passed to it. In your activity, you implement that interface and override the method. Once the method is called, you could create another method in AF2 which you can easily call and pass the corresponding values.
The above described process has been shown in this tutorial: how to communicate between fragments and activities
FragmentOne.java
public class FragmentOne extends Fragment{
private Activity activity;
#Override
public void onAttach(Activity act){
super.onAttach(act);
activity = act;
}
#Override
public View onCreateView(..........){
/* somethind was clicked here*/
try{
((OnSomethingClickedListener) activity).updateActivity(position);
}catch(ClassCastException e){}
return view;
}
public interface OnSomethingCllickedListener{
void updateActivity(int position);
}
}
In your activity, implement the interface and override the method above:
public class ActivityOne extends Activity implements FragmentOne.OnSomethingCllickedListener{
#Override
public void onCreate(Bundle saveInstanceState){
/* as usual here */
}
#Override
public void updateActivity(int position){
/* call FragmentTwo's method here to update the view based on the position of item clicked here*/
FragmentTwo.updateView(position);
}
}
Secondly, to decouple your activities from your fragments, use EventBus library. This is quite simple and goes like this:
Download the jar file and add it to your project.
Create an Event class
Register for Events in your activities (unregister inside onDestroy)
When you want to notify the activity of the events, just call EventBus' post method and pass back the respective data.
Inside your activity, you need a method onEvent(YourEventClassName event) then you can pass the values respectively to your fragments as needed.
I hope this helps.
Code to pass and retrieve data:
Bundle bundle =new Bundle();
bundle.putString("message", message);
Frag1 _fragment = new Frag1();
fragmentTransaction.replace(android.R.id.content, _fragment);
fragmentTransaction.commit();
Bundle bundle=getArguments(); //get data
if(bundle!=null)
{
message=bundle.getString("message") ;
}
i need to save a custom object that i use in a fragment so it will not be lost when the screen rotates (when the app calls onDestroy and then recalls onCreate)
now the normal way to do so is to implement Parcelable interface and save it to the bundle as a Parcelable object.
that is a very tedious way of doing things.
is there a way to just pass the object along as "putObject" method?
You can save your data in fragment, retained during a configuration change like in example.
Extend the Fragment class and declare references to your stateful
objects.
public class RetainedFragment extends Fragment {
// data object we want to retain
private MyDataObject data;
// this method is only called once for this fragment
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// retain this fragment
setRetainInstance(true);
}
.. getter and setter
}
Then use FragmentManager to add the fragment to the activity.
public class MyActivity extends Activity {
private RetainedFragment dataFragment;
#Override
public void onCreate(Bundle savedInstanceState) {
..
// find the retained fragment on activity restarts
FragmentManager fm = getFragmentManager();
dataFragment = (RetainedFragment) fm.findFragmentByTag(“data”);
// create the fragment and data the first time
if (dataFragment == null) {
// add the fragment
dataFragment = new DataFragment();
fm.beginTransaction().add(dataFragment, “data”).commit();
} else {
// available dataFragment.getData()
..
// save data in onDestroy dataFragment.setData(yourData);
The best way is to implement Parcelable (Faster).
Easier (not efficient) way is to implement Serializable and add the object into the bundle as serializable.
well searching i found no official way of doing so, so here are two "hacks" i found around the problem:
1)create a class that extends Application class, in it add an arrayList of objects.
inside onSaveInstanceState call:
getApplication().getObjectArray().add(YourObject);
save the Object index inside the bundle using putInt.
extract it inside the method onReturnestoreInstanceState.
2)my less favorite one:
android automatically saves the states of its views
therefor a way to save an object will be to create a view set its visibility to none so it wont show on the screen and then add each object we want to the view using the methods:
view.setTag(key,Object); or view.setTag(Object);
now inside onReturnestoreInstanceState get the view and extract the tags.
unfortunately i couldn't find a more simple way of saving an object
hope this one helps you out (in my app i ended up using the first method)
I have a Fragment Activity with a FragmentTabHost. I add the fragments to the tab using the following code:
mTabHost.addTab(mTabHost.newTabSpec(tab1Name).setIndicator(tabIndicator1),
EventSettingsStep1Fragment.class, null);
mTabHost.addTab(mTabHost.newTabSpec(tab2Name).setIndicator(tabIndicator2),
EventSettingsStep2Fragment.class, null);
When I switch to different tabs, I'd like to retain all the values (view state, etc) so that I have the same data when I switch back to the tab.
I overrode the onSaveInstanceState method & in there, I added values that I want retained to the bundle.
I ran through the methods being called and I have the following:
Switching from Tab1 to Tab2: Tab1:onPause then Tab2:onCreateView, Tab2:onResume
Switching from Tab2 to Tab1: Tab2:onPause then Tab1:onCreateView, Tab1:onResume
onSaveInstanceState is not being called.
Here is the code for one of my fragments:
public class EventSettingsStep1Fragment extends Fragment implements View.OnClickListener {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
Log.d(TAG, "onCreateView");
if (savedInstanceState != null) {
Log.d(TAG, "restoring onSavedInstanceState");
Gson gson = new Gson();
event = gson.fromJson(savedInstanceState.getString("event"), Event.class);
}
if (event != null) {
//set views
}
return v;
}
#Override
public void onResume() {
super.onResume();
Log.d(TAG, "onResume");
}
#Override
public void onPause() {
super.onPause();
Log.d(TAG, "onPause");
}
#Override
public void onSaveInstanceState(Bundle outState) {
Log.d(TAG, "onSaveInstanceState");
super.onSaveInstanceState(outState);
Gson gson = new Gson();
outState.putString("event", gson.toJson(event));
}
}
Why is onSaveInstanceState not being called? Is it only triggered through the FragmentActivity?
onSaveInstanceState is not being called because the framework simply reuses the already-existing instance of the fragment. onSaveInstanceState only gets called when the instance is about to be destroyed and then recreated. This happens for example when you rotate the display and force the hosting activity to be recreated.
onSaveInstanceState is also not called when you push a fragment on the backstack of a FragmentManager. You will have to restore the state from the already existing instance, which can be very annoying. See SO questions How can I maintain fragment state when added to the back stack? and Once for all, how to correctly save instance state of Fragments in back stack? for example.
Basically you will have to do what the answers to these questions suggest: continue using the values of your instance variables and do not rely on a saved instance state.