Develop Reference

Handle Fragment Backstack According to the Current Fragment

Problem 1
I have a Navigation Drawer and most of my fragment transactions happens from here.
So say I have 4 Items in my drawer and I am doing the transaction from all of them. So if I am at the fragment [A] and now I click on the fragment [B], I need to come back to the previous fragment i.e. [A]. But if I keep clicking on the Item B of the navigation drawer that opens the fragment [B], I keep adding it to the backstack and when I press the back button, I am still at the same fragment.
Problem 2
How do I achieve the Clear Top behavior that is used for the intents for the fragments. As intents have the power to clear the activities from the stack from the top only, I want to achieve the same behavior.

Problem 1 & 2 solution Idea:
Create an Interface say FragmentInstanceHandler
public interface FragmentInstanceHandler {
public void openFragment(Fragment fragment, String fragmentTag);
}
Create a BaseFragment like below and extend this to all your Fragment classes:
public BaseFragment extends Fragment {
public FragmentInstanceHandler fragmentInstanceHandler;
public void setFragmentInstanceHandler(FragmentInstanceHandler fragmentInstanceHandler) {
this.fragmentInstanceHandler = fragmentInstanceHandler;
}
}
Implement the FragmentInstanceHandler interface to the Activity in which you are going to open all the Fragments. Let's say Activity is MainActivity:
public MainActivity extends Activity implements FragmentInstanceHandler {
private BaseFragment currentFragment;
#Override
public void openFragment(BaseFragment fragment, String fragmentTag) {
FragmentManager fragmentManager = getSupportFragmentManager();
Fragment oldFragmentInstance = fragmentManager .findFragmentByTag(fragmentTag);
boolean fragmentPopped = fragmentManager.popBackStackImmediate (fragmentTag, 0);
if (!fragmentPopped && oldFragmentInstance == null) {
fragment.setFragmentInstanceHandler(this);
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.add(R.id.container, fragment, fragmentTag);
fragmentTransaction.addToBackStack(fragmentTag);
fragmentTransaction.commit();
currentFragment = fragment;
} else if(fragmentPopped ){
currentFragment = oldFragmentInstance;
}
if(mDrawerLayout!= null)
mDrawerLayout.closeDrawers();
}
}
Now whenever you want to open a new Fragment even from any other Fragment you can call method like below, It is advised to provide new tag if you want to have new instance of same Fragment:
fragmentInstanceHandler.openFragment(new MyFragment(), "FragmentNewInstance");
You can tweak FragmentInstanceHandlerto add your own method to replace the current Fragment instead of adding. Above solution just gives you an idea how you can acheive your solution by putting and mananging all your code from one place.

State of nested Fragments is lost when re-attached to their fragment container in bottom tab navigation

I am working on an app that has the following UI structure:
One Activity, called FoodActivity
This Activity implements bottom navigation. Hence, can show three categories of food: fruit, meat and fish
The Activity has a big Fragment container, where I attach the Fragment for fruit, meat and fish as the user interacts with the bottom tabs.
Each outer Fragment (fish, meat and fish) presents navigation between Fragments: it can show a list of fruits, and the the detail for the selected fruit.
Hence, the outer Fragments have another Fragment container in where I attach Fragments for the fruit list or fruit detail.
So, it's one main Activity, which has a big Fragment container where I swap Fragments, which in turn nest other Fragments
To switch from one outer Fragment to another using the tabs (ie: switch from fruit to meat), I perform a Fragment Transaction in the outer Fragment container:
private void switchFragment(Fragment fragment, String fragmentTag) {
final FragmentManager fm = getSupportFragmentManager();
final FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.fragment_outer, fragment, fragmentTag);
ft.commit();
}
The problem is that when switching the first-level Fragments, the state of their ChildFragmentManager is not kept.
For example, imagine that:
- I start in FuitFragment
- The FruitFragment, when created, attaches the nested FruitListFragment
- The user navigates in the nested Fragment container, from FruitListFragment to FruitDetailFragment
- The user switches to another tab
- The user switches back to the fruit tab
- The child `FragmentManager* of the FuitFragment does not automatically put FruitDetailFragment in the nested fragment container.
More specifically, when switching back to the outer Fragment:
onCreate is called, with savedInstance == null
onCreateView is called, with savedInstance == null
Hence, as the outer Fragment onCreate method is called, and I cannot tell whether or not to attach the child Fragment (as one usually does with Activities).
Moreover if I don't attach it (using an instance variable to check if I'm switching back to it) the child Fragment container will be just empty.
Experiments and notes
I have experimented that if I add the outer fragment transaction to the backstack when attaching it, when switching back to it, onCreate method is NOT called and the child FragmentManager will remember and attach the fragment it had before.
However, I cannot add it to the backstack as per Google's specifications on bottom navigation.
Setting setRetainInstace to true does not make any effect.
So, what should I do for properly restoring the state of the child FragmentManager?
Am I doing something wrong, or is it that everything around nested Fragments in Android is not well supported (or a bit broken) and I simply should not provide navigation using nested Fragments?

As Abbas pointed out, the problem was that I was using replace to switch between fragments.
I have changed to code in the Activity that puts the outer Fragment, and it works:
private void showChildFragment(int itemId) {
final FragmentManager fragmentManager = getSupportFragmentManager();
final FragmentTransaction transaction = fragmentManager.beginTransaction();
final Fragment currentFragment = getSupportFragmentManager().findFragmentById(R.id.fragment_outer);
if (currentFragment != null) {
Log.v(TAG, "Detaching item #" + currentFragment);
currentFragment.setMenuVisibility(false);
currentFragment.setUserVisibleHint(false);
transaction.detach(currentFragment);
}
// Do we already have this fragment?
final String tag = makeFragmentTag(container.getId(), itemId);
Fragment fragment = fragmentManager.findFragmentByTag(tag);
if (fragment == null) {
fragment = createFragmentForViewId(itemId);
Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
transaction.add(container.getId(), fragment, tag);
} else {
Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
transaction.attach(fragment);
}
fragment.setMenuVisibility(true);
fragment.setUserVisibleHint(true);
transaction.commitAllowingStateLoss();
fragmentManager.executePendingTransactions();
}
private Fragment createFragmentForViewId(int itemId) {
switch (itemId) {
case FRAGMENT_ID_LIBRARY:
return LibraryNavigationFragment.createInstance();
case FRAGMENT_ID_FEED:
return WebAppFragment.createInstance("feed");
case FRAGMENT_ID_SUGGEST:
return WebAppFragment.createInstance("suggest");
default:
throw new IllegalArgumentException();
}
}
This code is almost copy pasted from android.support.v4.app.FragmentPagerAdapter as ViewPagers using Fragments work like I wanted to.

With getChildFragmentManager() it won't crash.
private void switchFragment(Fragment fragment, String fragmentTag) {
final FragmentManager fm = getChildFragmentManager();
final FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.fragment_outer, fragment, fragmentTag);
ft.commit();
}

Handling the backstack with fragments containing tabs

I'm trying to create an Android application which contains a single activity with a container and a navigation drawer. The initialy empty container loads fragments which has a ViewPager inside a tab layout in which I load a frgment with a FragmentTransaction:
public static void replaceFragmentInContainer(FragmentManager fragmentManager, Fragment fragmentToShow,
boolean addToBackStack)
{
FragmentTransaction transaction = fragmentManager.beginTransaction();
if (addToBackStack)
{
transaction.addToBackStack(null);
}
transaction.replace(R.id.container, fragmentToShow);
transaction.commit();
}
I'm using v4 fragments with a v7 ActionBar in a v7 ActionBarActivity.
Every loaded fragment is a fragment which only loads tabs with other fragments which they hold the actual usability. An example of such tab loading fragment:
public class MainFragment extends TabsFragment
{
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
super.onCreateView(inflater, container, savedInstanceState);
View contentView = inflater.inflate(R.layout.fragment_main, container, false);
initTabsLayout(savedInstanceState, contentView, R.id.pager);
addTab("tabspectag1", "", R.drawable.draw1, Fragment1.class, null);
addTab("tabspectag2", "", R.drawable.draw2, Fragment2.class, null);
addTab("tabspectag3", "", R.drawable.draw3, Fragment3.class, null);
return contentView;
}
The problem I'm facing is with the backstack. When a fragment is added to the backstack and I press the back button, the app does go back to the previous fragment like I want to and I see the tabs layout itself, but the content of the tabs is empty like there was nothing loaded to that tab. When it happens, I manage to reload the tab's content only when choosing that screen again with the navigational drawer.
I've tried overriding the onBackPressed in the activity:
#Override
public void onBackPressed()
{
if (getFragmentManager().getBackStackEntryCount() > 0)
{
getFragmentManager().popBackStack();
} else
{
super.onBackPressed();
}
}
but that like I said, it's like I'm getting back to the previous fragment but the tab inside that fragment is not repainting the fragment it had.
What can be done to solve this issue?
Since I DO see the tabs layout of the original fragment in the backstack but not the fragment inside the tab, is it possible I just need to somehow refresh the tab content meaning repaint it? If I can do such a thing then how can I do it?

You didn't post the entire code but, bear in mind that when using fragments inside fragments, the outer fragment should use the childfragmentmanager instead of the regular fragment manager.
If you have an Activity, then you have a fragment that has a Viewpager and inside that viewpager the views are fragments, those outer fragments must use their own childfragmentmanager instead of the activities fragmentmanager.
Activity uses getFragmentManager() to instantiate and show new fragments. Fragments use getChildFragmentManager() to instantiate and show new inner fragments. (fragments inside fragments).
If you always use the same fragmentmanager to handle the transactions the behaviour will be unpredictable.
Your Viewpager should have an TabsAdapter associated that extends from FragmentStatePagerAdapter to show new fragments(and uses the getChildFragmentManager from the fragment instead of the activity).

ViewPager isn't loading the items after removed and re-added into FrameLayout

I'm trying to make a fragment to display tips for the user. The fragment's createView method returns a ViewPager and setup the PagerAdapter through AsyncTask. This fragment is added dinamically in the FragmentActivity when the user press a button. If the user reaches the last item of press the same button again, this fragment is removed from the FragmentActivity. It's important to note that I add the fragment to the FrameLayout idenfified by android.R.id.content.
Ok, the first time I press the button, it works as expected. But the second time I press the button, the ViewPager doesn't appear. When I use the View Hierarchy to see what's happenning, I see the ViewPager in the right place, but with no items. I debugged and noted that the getCount() of the PagerAdapter is called, but the getItem is never called.
This is the createView method of my fragment:
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View tipsView = inflater.inflate(R.layout.tip_manager_layout, container, false);
this.tipPagerAdapter = new TipPagerAdapter(getFragmentManager(), getArguments().getIntArray(TIP_LAYOUT_IDS_KEY));
this.viewPager = (ViewPager) tipsView.findViewById(R.id.tip_pager);
this.viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageSelected(int position) {
if(position == (tipPagerAdapter.getCount()-1)){
stop();
}
}
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
// Workaround to set the PagerAdapter within a fragment transaction
new SetViewPagerAdapterTask().execute();
return tipsView;
}
I add the fragment this way:
FragmentTransaction fragmentTransaction = fragmentActivity.getSupportFragmentManager().beginTransaction();
fragmentTransaction.add(android.R.id.content, this, TAG);
fragmentTransaction.commit();
And remove the fragment this way:
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.remove(tipManagerFragment);
fragmentTransaction.commit();
This is the layout inflated by the fragment:
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/tip_pager"
android:layout_width="fill_parent"
android:layout_height="175dp"
android:layout_gravity="center_horizontal|bottom"
android:paddingBottom="2dp" />
Could someone help me with this problem?
EDIT:
For a while, I'm using the show and hide methods of the fragment after adding it to the activity. But it's not the correct approach. I can't understand why I can't add again a fragment with a ViewPager. The ViewPager is added and removed correctly, but the second time, it simply doesn't show anything.

After a long time thinking about my problem, I had the following idea: maybe the problem is related to the fact that I'm removing the fragment that has the ViewPager, but I'm not removing the fragments used by the ViewPager. Then, these fragments continues in the FragmentManager and something strange happens when the new ViewPager tries to use them.
So, I started trying to remove all the fragments. To do this, I created a method in my FragmentPagerAdapter this way:
public void destroy(FragmentTransaction fragmentTransaction){
for(Fragment tipFragment : tipFragments){
fragmentTransaction.remove(tipFragment);
}
}
The adapter is using the tipFragments to create its content. So, I get a fragmentTransaction as parameter and I remove all these fragments. When I want to remove my fragment, I use this code:
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
tipPagerAdapter.destroy(fragmentTransaction);
fragmentTransaction.remove(TipManagerFragment.this);
fragmentTransaction.commit();
This way, I remove all the fragments and when I add the fragment which has the ViewPager again, everything works well.

Android added Fragment to screen, but taps fall through new Fragment view to the previous one

I'm working with Fragments for the first time and running into a weird behavior. I have an activity with a Fragment covering the entire view. It contains a ListView. When I tap on an item in the ListView, I want to show a details fragment which contains information about that item.
This is how I'm presenting the new fragment view:
FragmentManager fragmentManager = this.getActivity().getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
DetailsFragment fragment = new DetailsFragment();
transaction.add(R.id.viewRoot, fragment).setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
.addToBackStack("Details").commit();
R.id.viewRoot is the id of the root layout in the first Fragment's layout xml, so the new Fragment fills the entire screen.
My Problem: When the new fragment is visible and covering the entire screen, any clicks or taps which land on the background (i.e. not hitting a button or textfield on the new fragment) appear to be going through the view and landing on the first fragment. So, I tap on a ListView item, which causes the DetailsFragment to get added to the screen. Then when I tap on the background of the DetailsFragment, that tap falls through and lands on the ListView causing another DetailsFragment to be added for whatever item I happened to hit behind the scenes.
Am I adding my new fragment incorrectly? Why are my clicks/taps falling through?
EDIT for caiuspb:
public class BaseFragment extends Fragment {
public void pushNewFragment(Fragment fragment, String description) {
FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.remove(this);
transaction.add(R.id.viewRoot, fragment).setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
.addToBackStack(description).commit();
}
}
All of my fragments extend my BaseFragment class.

I experimented with the suggestions I received, but none of them worked. In the end, my solution was to add an OnTouchListener to the root view of my subfragments which discarded all touches.
View view = inflater.inflate(R.layout.mylayout, container, false);
view.setOnTouchListener(new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
return true;
}
});

There is another post here on StackOverflow about that strange Fragment behaviour. Try to remove your Fragment before you add it because the replace Method seems to be buggy
edit:
Move the Fragment logic into your Activity because your activity contains your Fragments. Today I tried to use the FragmentActivity and Fragments from the Android Support Library. Now I can use the replace method withouht any bugs. This is my approach and this works:
public class DashActivity extends FragmentActivity{
...
private void changeRightFragment(Fragment fragment) {
Log.i(TAG, "Loading Fragment into container: " + fragment.getClass().toString());
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.rightfrag, fragment);
// Add a transition effect
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
// Add the Fragment to the BackStack so it can be restored by
// pressing the Back button
ft.addToBackStack(null);
ft.commit();
}
...
public void setUserFragment(User user) {
UserFragment fragment = new UserFragment(user);
changeRightFragment(fragment);
}
So if you want to invoke a changeFragment method from inside your Fragment use a callback mechanism to the Activity