I need to display multiple set of instructions to the user. For each instruction(FragmentA) the user can navigate to another screen (FragmentA1). I have used a ViewPager that hold list of fragments. When user navigates to the first fragment(FragmentA) the user can click a button and move to a (FragmentA1) detailed view of the instruction. So each page of the viewpager is capable of opening another fragment.
All works fine till here. Issue I am facing is with the backstack. The activity with the viewpager adapter handles the moveToNext() and moveToPrevious() methods. Below is my implementation of onBackPressed() method:
#Override
public void onBackPressed() {
FragmentManager fm = getSupportFragmentManager();
for (Fragment frag : fm.getFragments()) {
if (frag.isVisible()) {
FragmentManager fm = frag.getFragmentManager();
if (fm.getBackStackEntryCount() > 0) {
fm.popBackStack();
return;
} else {
moveToPrevious();
return;
}
}
}
super.onBackPressed();
}
With the above implementation is:
If I traverse FragA->FragA1->FragB->FragB1->FragC->FragC1
When I am at FragC1 and I press back button, then I am directly navigated to FragB1 instead of FragC and then to FragA1. I need to follow the same path backwards as traversed forward.
I am not sure what is wrong but it is not able to pop the nested fragment and display its parent fragment.
Shouldn't fm.popBackStack() show the parent fragment ?
I solved it this way. Get the fragment that is visible. When there are no child fragments to pop anymore just move to previous page.
#Override
public void onBackPressed() {
FragA fragment = (FragA) pagerAdapter.instantiateItem(viewPager, viewPager.getCurrentItem());
if (fragment.getChildFragmentManager().getBackStackEntryCount() != 0) {
fragment.getChildFragmentManager().popBackStack();
}
else {
moveToPrevious();
}
}
Related
My app contains one empty activity and a couple of fragments. The onCreate of the activity replaces the empty view in activity_main.xml with a MainFragment that contains some buttons. Each button launches a separate fragment, and user can navigate from one fragment to another, etc.
On the press of back key, the current fragment correctly gets replaced with the previous fragment, until you get to the MainFragment. When user presses back from MainFragment, it hides the main fragment and you see the white empty background of the main activity. But I want to exit from the activity at this point, as that would be the sensible behaviour.
I am able to achieve this by calling super.onBackPressed() for a second time from onBackPressed if there are no fragments left in the fragment manager.
#Override
public void onBackPressed() {
super.onBackPressed();
FragmentManager manager = getSupportFragmentManager();
List<Fragment> fragments = manager.getFragments();
if (fragments == null || fragments.size() == 0) {
Log.d(TAG, "No more fragments: exit");
super.onBackPressed();
}
}
Is this acceptable thing to do - would it create any issues in the activity workflow? Is there a better/standard way to handle this scenario?
There is no problem to do that, but probably it would be easier if when you add the main fragment to the activity you do NOT call .addToBackStack()
You don't really need to override onBackPressed in your Activity. I would suggest implementing a method for adding fragments in your Activity:
protected void addFragment(Fragment fragment, boolean addToBackStack) {
String tag = fragment.getClass().getName(); //It's optional, may be null
FragmentTransaction transaction = getSupportFragmentManager()
.beginTransaction()
.add(R.id.your_container_id, fragment, tag);
if (addToBackStack) {
transaction.addToBackStack(tag);
}
transaction.commit();
}
And modify your onCreate method of activity like in the following snippet:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
// Add your fragment only if it is a first launch,
// otherwise it will be restored by system
addFragment(new YourFirstFragment(), false);
}
}
For all other fragments use:
addFragment(new OtherFragment(), true);
I've created a fragment that shows gridview and when any griditem is clicked it leds to another fragment. But when I press the physical backbutton the app closes instead of going back to previous fragment (i.e. fragment containing gridview). How can I solve this?
try this one
#Override
public void onBackPressed() {
if (getFragmentManager().getBackStackEntryCount() > 0 ){
getFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}
'addToBackStack' is used for moving back to previous fragment, you can use a common Function
in your Main activity for changing fragment.
public void change_fragment(Fragment fragment, int frame) {
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction trans = manager.beginTransaction();
//trans.setCustomAnimations(R.anim.enterfrom_left, R.anim.exit_to_right,R.anim.enterfrom_left, R.anim.exit_to_right);
trans.replace(frame, fragment);
trans.addToBackStack("hai" + frame);
trans.commit();
}
you can call it from Main activity like this
change_fragment(new Frag(),R.id.fl_main_frag_container);
you can call it from another fragment like this
((MainActivity)getContext()).change_fragment(new Frag(), R.id.fl_main_frag_container);
I have 4 fragments in a FragmentPagerAdapter.
When I am in the 4th fragment and press the back button, it can be returned to previous fragment, it may be the 3rd or 2nd fragment.
But If the previous one is the 3rd one, the app will automatically exit after clicking the back button. What I want is the app can stay on the 3rd fragment after user click the back button on the 4th fragment without automatically exiting. The reason why it happens is because that the two neighbored fragments will taking actions synchronously when user click back button.
How to implement it? Thx.
public void onBackPressed() {
moveTaskToBack(true);
System.out.println(123456);
ViewPager mViewPager = (ViewPager) this.findViewById(R.id.pager);
App atp = this.getApplication();
int count = atp.getFragmentStack().size();
if (count == 0) {
//additional code
} else {
mViewPager.setCurrentItem(2);
}
}
UPDATES（answering comment 1）：
My app use FragmentPagerAdapter ,
so I want to use
ViewPager mViewPager = (ViewPager) this.findViewById(R.id.pager);
mViewPager.setCurrentItem(2);
to chang the fragment. Commit does not work, I also need to change the selection bar.
You need to add to back stack your fragments or replace:
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(here_your_fragment);
//OR ADD
//fragmentTransaction.add(here_your_fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
So for you solution is:
In activity create variable
public int fragmentPosition;
Then, put the value of your activity or fragment into your adaper. In method where your fragments instantiate or gets pass the position of your fragment to the value of fragmentPosition, like this
yourActivityOrFragment.fragmentPosition = position;
And after that, in method onBackPressed() check for position of fragments
public void onBackPressed() {
if (fragmentPosition == 3) {
finish();
} else {
super.onBackPressed();
}
}
I have an Activity and many fragments inflated in same FrameLayout
<FrameLayout
android:id="#+id/content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
example: mainActivity > any fragment (press back button) > activity is blank.
In onCreate:
layout = (FrameLayout)findViewById(R.id.content_frame);
layout.setVisibility(View.GONE);
When I start a fragment:
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, profileFragment);
ft.addToBackStack(null);
ft.commit();
layout.setVisibility(View.VISIBLE);
I suppose I need to make the frameLayout's visibility GONE again on back pressed, but how do I do this?
I tried onBackPressed and set layout.setVisibility(View.GONE); but I cannot go back through fragments, as I go directly to main page.
If you have more than one fragment been used in the activity or even if you have only one fragment then the first fragment should not have addToBackStack defined. Since this allows back navigation and prior to this fragment the empty activity layout will be displayed.
// fragmentTransaction.addToBackStack() // dont include this for your first fragment.
But for the other fragment you need to have this defined otherwise the back will not navigate to earlier screen (fragment) instead the application might shutdown.
#Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
}
else {
int fragments = getSupportFragmentManager().getBackStackEntryCount();
if (fragments == 1) {
finish();
} else if (getFragmentManager().getBackStackEntryCount() > 1) {
getFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}
}
To add a fragment
getSupportFragmentManager().beginTransaction()
.replace(R.id.layout_main, dashboardFragment, getString(R.string.title_dashboard))
.addToBackStack(getString(R.string.title_dashboard))
.commit();
Sorry for the late response.
You don't have to add ft.addToBackStack(null); while adding first fragment.
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, profileFragment);
// ft.addToBackStack(null); --remove this line.
ft.commit();
// ... rest of code
If you want to track by the fragments you should override the onBackPressed method, like this
public void onBackPressed() {
if (getFragmentManager().getBackStackEntryCount() == 1) {
finish();
} else {
super.onBackPressed();
}
}
You can override onBackPressed and check to see if there is anything on the backstack.
#Override
public void onBackPressed() {
int fragments = getFragmentManager().getBackStackEntryCount();
if (fragments == 1) {
// make layout invisible since last fragment will be removed
}
super.onBackPressed();
}
Just don't add the first fragment to back stack
Here is the Kotlin code that worked for me.
val ft = supportFragmentManager.beginTransaction().replace(container, frag)
if (!supportFragmentManager.fragments.isEmpty()) ft.addToBackStack(null)
ft.commit()
On a recent personal project, I solved this by not calling addToBackStack if the stack is empty.
// don't add the first fragment to the backstack
// otherwise, pressing back on that fragment will result in a blank screen
if (fragmentManager.getFragments() != null) {
transaction.addToBackStack(tag);
}
Here's my full implementation:
String tag = String.valueOf(mCurrentSectionId);
FragmentManager fragmentManager = mActivity.getSupportFragmentManager();
Fragment fragment = fragmentManager.findFragmentByTag(tag);
if (fragment != null) {
// if the fragment exists then no need to create it, just pop back to it so
// that repeatedly toggling between fragments doesn't create a giant stack
fragmentManager.popBackStackImmediate(tag, 0);
} else {
// at this point, popping back to that fragment didn't happen
// So create a new one and then show it
fragment = createFragmentForSection(mCurrentSectionId);
FragmentTransaction transaction = fragmentManager.beginTransaction()
.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
.replace(R.id.main_content, fragment, tag);
// don't add the first fragment to the backstack
// otherwise, pressing back on that fragment will result in a blank screen
if (fragmentManager.getFragments() != null) {
transaction.addToBackStack(tag);
}
transaction.commit();
}
irscomp's solution works if you want to end activity when back button is pressed on first fragment. But if you want to track all fragments, and go back from one to another in back order, you add all fragments to stack with:
ft.addToBackStack(null);
and then, add this to the end of onCreate() to avoid blank screen in last back pressed; you can use getSupportFragmentManager() or getFragmentManager() depending on your API:
FragmentManager fm = getSupportFragmentManager();
fm.addOnBackStackChangedListener(new OnBackStackChangedListener() {
#Override
public void onBackStackChanged() {
if(getSupportFragmentManager().getBackStackEntryCount() == 0) finish();
}
});
Final words: I don't suggest you to use this solution, because if you go from fragment1 to fragment 2 and vice versa 10 times, when you press back button 10 times it will do it in back order which users will not want it.
Almost same as Goodlife's answer, but in Xamarin.Android way:
Load fragment (I wrote helper method for that, but it's not necessary):
public void LoadFragment(Activity activity, Fragment fragment, string fragmentTitle = "")
{
var fragmentManager = activity.FragmentManager;
var fragmentTransaction = fragmentManager.BeginTransaction();
fragmentTransaction.Replace(Resource.Id.mainContainer, fragment);
fragmentTransaction.AddToBackStack(fragmentTitle);
fragmentTransaction.Commit();
}
Back button (in MainActivity):
public override void OnBackPressed()
{
if (isNavDrawerOpen()) drawerLayout.CloseDrawers();
else
{
var backStackEntryCount = FragmentManager.BackStackEntryCount;
if (backStackEntryCount == 1) Finish();
else if (backStackEntryCount > 1) FragmentManager.PopBackStack();
else base.OnBackPressed();
}
}
And isNavDrawerOpen method:
bool isNavDrawerOpen()
{
return drawerLayout != null && drawerLayout.IsDrawerOpen(Android.Support.V4.View.GravityCompat.Start);
}
I still could not fix the issue through getBackStackEntryCount() and I solved my issue by making the main page a fragment too, so in the end I have an activity with a FrameLayout only; and all other fragments including the main page I inflate into that layout. This solved my issue.
I had the same problem when dealing with Firebase's Ui Login screen. When back button was pressed it left a blank screen.
To solve the problem I just called finish() in my onStop() method for said Activity. Worked like a charm.
If you have scenario like me where a list fragment opens another details fragment, and on back press you first need to show the list fragment and then get out the whole activity then, addToBackStack for all the fragment transactions.
and then on the activity, do like this (courtesy: #JRomero's answer, #MSaudi's comment)
#Override
public void onBackPressed() {
int fragments = getFragmentManager().getBackStackEntryCount();
if (fragments == 1) {
// make layout invisible since last fragment will be removed
}
super.onBackPressed();
}
Just Comment or Remove transaction.addToBackStack(null) in your code.Below is code to change fragment in kotlin.
fun ChangeFragment(activity: MainActivity, fragment: Fragment) {
val transaction: FragmentTransaction =
activity.getSupportFragmentManager().beginTransaction()
transaction.replace(R.id.tabLayoutContainer, fragment)
transaction.commit()
}
Does the Back Stack support interaction with nested Fragments in Android?
If it does, what am I doing wrong? In my implementation, the back button is completely ignoring the fact that I added this transaction to the back stack. I'm hoping it is not because of an issue with nested fragments and just me doing something incorrectly.
The following code is inside of one of my fragments and is used to swap a new fragment with whatever nested fragment is currently showing:
MyFragment fragment = new MyFragment();
FragmentTransaction ft = getChildFragmentManager().beginTransaction();
ft.setCustomAnimations(R.animator.slide_in_from_right, R.animator.slide_out_left, R.animator.slide_in_from_left, R.animator.slide_out_right);
ft.addToBackStack(null);
ft.replace(R.id.myFragmentHolder, fragment);
ft.commit();
I have the same problem, I would like to nest fragments, and to keep a back stack for each nested fragment.
But... it seems that this case is not handled by the v4 support library. In the FragmentActivity code in the library, I can find :
public void onBackPressed() {
if (!mFragments.popBackStackImmediate()) {
finish();
}
}
The mFragments represents the FragmentManager of the activity, but it does not seem this manager "propagates" the pop to children managers.
A workaround would be to manually call the popBackStackImmediate() on the child manager, like this in the activity inherited from FragmentActivity :
private Fragment myFragmentContainer;
#Override
public void onBackPressed() {
if (!myFragmentContainer.getChildFragmentManager().popBackStackImmediate()) {
finish(); //or call the popBackStack on the container if necessary
}
}
There might be a better way, and a more automated way, but for my needs it is allright.
In my current project we have multiple "nested layers" so I've come up with following workaround to automatically pop backstack only for top level fragment managers:
#Override
public void onBackPressed() {
SparseArray<FragmentManager> managers = new SparseArray<>();
traverseManagers(getSupportFragmentManager(), managers, 0);
if (managers.size() > 0) {
managers.valueAt(managers.size() - 1).popBackStackImmediate();
} else {
super.onBackPressed();
}
}
private void traverseManagers(FragmentManager manager, SparseArray<FragmentManager> managers, int intent) {
if (manager.getBackStackEntryCount() > 0) {
managers.put(intent, manager);
}
if (manager.getFragments() == null) {
return;
}
for (Fragment fragment : manager.getFragments()) {
if (fragment != null) traverseManagers(fragment.getChildFragmentManager(), managers, intent + 1);
}
}
As of API 26 there is a setPrimaryNavigationFragment method in FragmentTransaction that can be used to
Set a currently active fragment in this FragmentManager as the primary navigation fragment.
This means that
The primary navigation fragment's child FragmentManager will be called first to process delegated navigation actions such as FragmentManager.popBackStack() if no ID or transaction name is provided to pop to. Navigation operations outside of the fragment system may choose to delegate those actions to the primary navigation fragment as returned by FragmentManager.getPrimaryNavigationFragment().
As mentioned by #la_urre in the accepted answer and as you can see in FragmentActivity's source, the FragmentActivity's onBackPressed would call its FragmentManager's popBackStackImmediate() which in turn would check whether there is an mPrimaryNav (primary navigation, I assume) fragment, get its child fragment manager and pop its backstack.
#Override
public void onBackPressed() {
FragmentManager fm = getSupportFragmentManager();
if (fm.getBackStackEntryCount() > 0) {
fm.popBackStack();
return;
}
finish();
}