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Android: Prevent fragment from becoming "active" while replacing another

I have the following invocations:
context.getSupportFragmentManager().popBackStack(tag.name(), 1);
context.getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment, tag.name()).addToBackStack(tag.name()).commit();
...while I have at least 2 other fragments on the backstack that were opened before. When these two commands will be executed and the latest fragment has been popped off the backstack, for a very short period of time, the fragment before this fragment is going to be active before the popped fragment has been replace by the given one. And that's the problem, because this fragment fetches data from server and is displaying a progress dialog. Sometimes this leads to race conditions and strange behaviour.
How can I prevent the "non-active" fragments from becoming active while replacing another fragment?
Here is a short explanation of the situation:
MainActivity -> opens Fragment1 -> opens Fragment2a -> opens EditActivity -> after "save action", Fragment2a will be popped and a new Fragment2b will be added into the fragment_container of the MainActivity. While this happens, Fragment1 is doing things, but it must not do this. I want to prevent Fragment1 to do any tasks. It should somehow just stay in background and "sleep".

What about using observer pattern? You create an interface with a method to set fragments to busy starte or do some logic.
All fragments implement this interfac and you create a list that contains these interface inside Activity. If a fragment is registered add this fragments to list or remove them with unregister methods for example.
(MyActivity)getActivity.register(this); can be called to register a fragment. Or you can call a method like in active fragment if you wish to set other fragments except this one as busy (MyActivity)getActivity.setActive(this) and inside MyActivity you can declare this method as
public void setActive(IStateController fragment) {
for(IStateController f: listOfSubscribers) {
if(f == fragment) {
// This fragment called the method and should active
// other fragments can be set to busy or waiting state
}
}
}
I really can't say if it works for you but interacting with fragments without being aware of each other can be done this way, or you can check EventBus library.

Just check
if(getActivity() == null || !isAdded){
return; //don't do your code that touches UI if it is not active.
}
but make sure you have your onPause remove your busy indicator then if you don't plan to wait for completion or you will create a memory leak of window leaking.

I'm not sure if I misuse the fragment manager concept so that this situation can occur or if the fragment manager concept is a total crap (like a lot in Android), but I solved it by using some workaround. When I start or replace a new fragment, I store immediately an ID in the application context. When a Fragment is getting started, it checks if is has the correct id. If not, I return a null view and the fragment won't be created. The check looks like this:
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState)
{
return FragmentCreationHelper.createFragmentView(inflater, container, TAG, getFragmentId(), R.layout.fragment_mycoolview);
}
The helper class...
public class FragmentCreationHelper
{
public static View createFragmentView(LayoutInflater inflater, ViewGroup container, String loggingTag, FragmentTag fragmentId, int template)
{
Log.d(loggingTag, "onCreateView()");
if (MyContext.getNextVisibleFragment() == null || fragmentId.equals(MyContext.getNextVisibleFragment()))
{
Log.d(loggingTag, "inflating view...");
return inflater.inflate(template, container, false);
}
else
{
Log.d(loggingTag, "Skipping view inflation. Fragment should not be displayed.");
return null;
}
}
}

Communicating between fragments within an activity

I am trying to write a test app which contains an activity. There are two fragments inside this activity, which are defined as LeftFragment and RightFragment. I used getFragmentManager().findFragmentById() to get connection from each other fragments. By using that methode I am able to get an LeftFragment object from RightFragment, but not RightFragment object from LeftFragment. It just works only oneway. I am doing this, because I want to call some operations from other fragment, that return some values. I was thinking about using EventBus but I failed too. How can I achive that?
Here is my LeftFragment
public class LeftFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
RightFragment rightFragment = (RightFragment) getFragmentManager().findFragmentById(R.id.rightFragment);
if (rightFragment != null){
makeToast(rightFragment.getMessageFromRight());
}else {
makeToast("does not found rightFragment");
}
return inflater.inflate(R.layout.fragment_left, container, false);
}
public String getMessageFromLeft(){
return "Hi! Im left";
}
private void makeToast(String text){
Toast.makeText(getContext(),text,Toast.LENGTH_SHORT).show();
}
}
And here is my RightFragment
public class RightFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
LeftFragment leftFragment = (LeftFragment) getFragmentManager().findFragmentById(R.id.leftFragment);
if (leftFragment != null){
makeToast(leftFragment.getMessageFromLeft());
}else {
makeToast("does not found leftFragment");
}
return inflater.inflate(R.layout.fragment_right, container, false);
}
public String getMessageFromRight(){
return "Hi! Im right!";
}
private void makeToast(String text){
Toast.makeText(getContext(),text,Toast.LENGTH_SHORT).show();
}
}

There are many ways to communicate between 2 fragments . If 2 fragments loaded at the same time. I usaually use one of 2 ways below to do it.
You can use this link using obserable pattern to communication 2 fragments.
you can use EventBus lib for communication, it 's very simple
Your issue:
By using that methode I am able to get an LeftFragment object from
RightFragment, but not RightFragment object from LeftFragment
I think your problem is LeftFragment is intitialized previous, so you can find it from RightFragment. Your solution is ok, using EventBus. YOu need to review your codes to find the issue. You can test by creating other methods, after 2 fragment was initialized.
For ex: click button in LeftFragment, toast a message in RightFragment.

Probably what is happening is that the Left Fragment is getting the OnCreateView() call first, at which point the Right Fragment has not been inflated yet (therefore it can't be "found" by findFragmentbyId()).
I would suggest moving the code that gets the references to the other fragments into onStart(), and only inflate the fragments in onCreateView().

How can I maintain a child view's state when switching fragments?

I am having a hard time understanding how the fragment lifecycle relates to switching between fragments in the back stack. Please bear with me if my question exposes more than one misconception.
Here is my code:
public class SomeFragment extends Fragment {
private SomeCustomView customView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.some_fragment, container, false);
return view;
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
// Create the child view
customView = (SomeCustomView) getView().findViewById(R.id.some_fragment_child_view);
customView.initializeMyCustomView();
}
}
As you can see, my fragment has a child view. The child view is a custom one. Here's code:
public class SomeCustomView extends SurfaceView implements SurfaceHolder.Callback {
private boolean aVariableWhichMustPersistForLifetimeOfApplication;
}
Whenever this fragment is added to the back stack and then later restored, the variable customView is recreated, and so I loose the value of aVariableWhichMustPersistForLifetimeOfApplication. This is creating all sorts of problems for me.
The application started out using an Activity that only displayed SomeCustomView and there were no fragments. Now I have to add functionality and so I have turned the custom view into a fragment, and thus I arrive at this problem.

I found an answer which works for me. The FragmentTransaction class has a number of methods which allow you to switch fragments in/out. (Android documentation for FragmentTransaction is here and a great StackOverflow explanation is here.)
In my case, I wanted SomeFragment to never loose the data contained in its view. To do this, use this code:
SomeFragment fragment = new SomeFragment();
FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.add(R.id.activity_fragment_placeholder, fragment, "some_fragment");
transaction.commit();
and then later:
getFragmentManager().beginTransaction().hide(fragment).commit();
You can now add/attach a different fragment to R.id.activity_fragment_placeholder. Notice that I'm using hide() rather than replace(), that's the key difference that keeps the view from being destroyed. When you want the fragment back, you can use show() or Android will do this automatically when the user clicks "Back" if you use addToBackStack() when adding/attaching your other fragment.

Unable to access layout inflater as child view has not initialised

I have an Android activity that searches a web service for new content to display then either displays a NoResultFragment or a ResultFragment which represents a swipe stack for the user to swipe through the items returned. Because I need to manage the stack, retrieving more data in the background as the stack gets low etc from the Activity, all of the stack details are held at the activity level and the yes/no actions trigger methods on the activity. All good so far.
The problem is I am using the layout inflater in the ResultFragment class to generate dynamic child Views, each one of which represents an item on the stack. These then get returned to the Activity controller which manages them, sends them to the fragment to display, hides them, moves them around etc, so I need access to the child item Views from the activity to do all this. I need to generate the actual child views from within the ResultFragment though, as that is where they will be visually displayed.
I create the ResultFragment, set it to the content area and then try and generate the child views by calling into the fragment created. The error is that the onViewCreate() method has not yet been called on the ResultFragment class as it has only just been added to the content frame, so there is no layoutinflater and my method to return the child View fails. I get the feeling there is something off with my design here, can someone shed some light on how to do this? Is it as simple as just passing through the parent layoutinflater from the Activity class?
Child view creation method
public View getChildView(StorySeed seed, int seedIndex)
{
final View m_view = inflater.inflate(R.layout.fragment_item, null); // Code to populate the view
return m_view;
}
activity method
private void initialiseResults(ArrayList<StorySeed> storySeeds) {
resultsFragment = new ResultsFragment(storySeeds, getApplicationContext());
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.content_frame, resultsFragment)
.commit();
// load the first results to screen
seedIndex = 1;
for (int i = 0; i < seedsToDisplay; i++) {
getNextToStack();
}
}
It is the call to getNextToStack() that is going into the Fragment class and calling the getChildView() method

I would suggest that you create the views in the activity (the controller) and pass them to the fragment as needed. The fragment is your MVC "view" and it should only tell the controller what happened. The controller decides what to do after that.
The way you can have one fragment replace itself by another is to call a method on the activity. Here's a quick example:
interface IAppController {
void onResultsNotFound();
}
class MyActivity extends Activity implements IAppController{
....
public void onResultNotFound(){
//switch fragments
}
}
class MyFragment {
....
void myMethod(){
IAppController controller = (IAppController) getActivity();
controller.onResultsNotFound();
}
}
Hope this helps

Is onCreateView() the constructor of Fragment class?

I am creating a fragment and adding it to a layout using java code. To do this, i created 2 classes and 2 layouts. One of the classes extends Fragment and other extends FragmentActivity. One of the xml files is the container and other is the fragment. Here is my code:
public class FragmentClass extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_layout, container,false);
return v;
}
}
And here is how i add the fragment to the layout:
public class Fragment_Activity extends FragmentActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.container_layout);
FragmentManager fm = getSupportFragmentManager();
Fragment fragment = fm.findFragmentById(R.id.container_layout_eklenecek_yer);
if(fragment==null){
fragment=new FragmentClass();
fm.beginTransaction().add(R.id.container_layout_eklenecek_yer, fragment).commit();
}
}
}
This code works as i expect, but here is my question: I have a piece of code in Fragment_Activity class that says:
fragment=new FragmentClass();
and FragmentClass has no constructors. Is a default, empty constructor is called here, or onCreateView works as a constructor? I am confused here.
Thanks

No.
You need a default constructor with fragments, a constructor that takes no arguments is a "default constructor" (this might be c++ terminology) because it allows you to construct an object, for certain.
Because Android might need RAM or something it can kill your fragments, it might also bring them back.
If you pass stuff to the constructor how will the Android OS know that stuff to pass it to you when it needs to re-create the fragment? It doesn't - this question has no answer.
Hence the default constructor.
When re-creating your fragment Android will attach an activity, and you can use onActivityAttached (or something to that tune, look up fragment life-cycles) to get the activity. If you know the activity implements/extends a whatever you can cast that activity to a whatever and store it, whatever you need to do.
The onCreateview method is what the name says: the thing that is called that returns a view. It is called when Android wants the view that represents your fragment, it is NOT a constructor, neither to be thought of, or in actual fact.