Overlapping hidden fragments after application gets killed and restored

Question

I'm switching between fragments by hiding the last fragment and adding a new one (See code below) - adding it to the back-stack as well. This way, users can quickly switch between the fragments without reloading the fragment data.

This works well until the app is killed (Scenario: users uses several other apps and my app is getting persisted and killed).

When a user opens the app, it is being restored and all the fragments are shown - overlapping one another.

Question: How can the restored fragments be restored with their hidden state? Perhaps I'm missing some flag? somewhere? Perhaps there is a better solution for fast switching between fragments (without reloading the data)?

Sample code of adding fragments - invoked several times with different fragments upon clicking somewhere:

FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction(); fragmentTransaction.hide(lastFragment); fragmentTransaction.add(newFragment); fragmentTransaction.addToBackStack(null); fragmentTransaction.commit(); lastFragment = newFragment; 

Answer 1

Hope somebody finds a better solution. I'll wait for one before I accept my solution:

In general, I use generated tags to find the unhidden fragments and hide them.

In details, I generate a unique tag for each fragment (StackEntry) and stack the tags as the fragments themselves get stacked. I persist the stack in the bundel and load it when the app gets restored in order to continure using it. Then I use the list of tags to find all of the unhidden fragments and hide them - except for the last one.

Heres sample code:

public class FragmentActivity extends Activity {      private static final String FRAGMENT_STACK_KEY = "FRAGMENT_STACK_KEY";      private Stack<StackEntry> fragmentsStack = new Stack<StackEntry>();      public FragmentActivity() {     }      @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);          setContentView(R.layout.content_frame);          if (savedInstanceState == null) {             // Init for the first time - not restore             // ...         } else {             Serializable serializable = savedInstanceState.getSerializable(FRAGMENT_STACK_KEY);             if (serializable != null) {                 // Workaround Android bug.                 // See: http://stackoverflow.com/questions/13982192/when-using-an-android-bundle-why-does-a-serialised-stack-deserialise-as-an-arra                 // And: https://code.google.com/p/android/issues/detail?id=3847                 @SuppressWarnings("unchecked")                 List<StackEntry> arrayList = (List<StackEntry>) serializable;                 fragmentsStack = new Stack<StackEntry>();                 fragmentsStack.addAll(arrayList);             }              // Hide all the restored fragments instead of the last one             if (fragmentsStack.size() > 1) {                 FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();                 for (int i = 0; i < fragmentsStack.size()-1; i++) {                     String fragTag = fragmentsStack.get(i).getFragTag();                     Fragment fragment = getFragmentManager().findFragmentByTag(fragTag);                     fragmentTransaction.hide(fragment);                 }                 fragmentTransaction.commit();             }         }         getFragmentManager().addOnBackStackChangedListener(new OnBackStackChangedListener() {             @Override             public void onBackStackChanged() {                 Fragment lastFragment = getLastFragment();                 if (lastFragment.isHidden()) {                     FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();                     fragmentTransaction.show(lastFragment);                     fragmentTransaction.commit();                 }             }         });     }      private Fragment getLastFragment() {         if (fragmentsStack.isEmpty()) return null;         String fragTag = fragmentsStack.peek().getFragTag();         Fragment fragment = getFragmentManager().findFragmentByTag(fragTag);         return fragment;     }      @Override     protected void onSaveInstanceState(Bundle outState) {         super.onSaveInstanceState(outState);         outState.putSerializable(FRAGMENT_STACK_KEY, fragmentsStack);     }      @Override     public void onBackPressed() {         if (!fragmentsStack.isEmpty()) {             fragmentsStack.pop();         }     }      public void switchContent(Fragment fragment) {         FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();         Fragment lastFragment = getLastFragment();         if (lastFragment != null) {             fragmentTransaction.hide(lastFragment);         }         String fragTag;         if (fragment.isAdded()) {             fragmentTransaction.show(fragment);             fragTag = fragment.getTag();         } else {             fragTag = Long.toString(System.currentTimeMillis());             fragmentTransaction.add(R.id.content_frame, fragment, fragTag);         }         if (!isFirstFragment()) {             // Add to backstack only the first content fragment and not the state before (that has nothing)             fragmentTransaction.addToBackStack(null);         }         fragmentTransaction.commit();          fragmentsStack.push(new StackEntry(fragTag));     }      public boolean isFirstFragment() {         return fragmentsStack.size() == 0;     }      private static class StackEntry implements Serializable {         private static final long serialVersionUID = -6162805540320628024L;          private String fragTag = null;         public StackEntry(String fragTag) {             super();             this.fragTag = fragTag;         }         public String getFragTag() {             return fragTag;         }     }       public static class Intent extends android.content.Intent {         public Intent(Context packageContext) {             super(packageContext, FragmentActivity.class);         }     } }