Develop Reference

fragment transaction - pop backstack and then add fragment

I am trying to do the following use case in Android Fragments. I have 2 fragments.
Fragment A -> Fragment B
When a user does something in Fragment B, I want to have the back stack as follows
Fragment A -> Fragment C. So, when the user presses back I want the user to go back to Fragment A.
I have tried the following
mFragmentManager.popBackStackImmediate();
FragmentTransaction fragmentTransaction = fMgr.beginTransaction()
.replace(R.id.base, Fragment_C, "1")
.addToBackStack(null)
.commitAllowingStateLoss();
The problem here is that I can see Fragment A for a short period of time before Fragment C is shown
If I do the following
mFragmentManager.popBackStackImmediate();
FragmentTransaction fragmentTransaction = fMgr.beginTransaction()
.replace(R.id.base, Fragment_C, "1")
.addToBackStack(null)
.commitNowAllowingStateLoss();
I get the error
This transaction is already being added to the back stack
I can get Fragment C to show up if I do this BUT
mFragmentManager.popBackStackImmediate();
FragmentTransaction fragmentTransaction = fMgr.beginTransaction()
.replace(R.id.base, Fragment_C, "1")
.commitNowAllowingStateLoss();
This works and I don't see Fragment A and see Fragment C but the back button takes the user out of the application. So, is it possible that we can pop the back stack of the fragment and then add another fragment to the back stack w/o showing Fragment A AND the back button takes the user back to Fragment A

Here is an easy method to add fragments to fragments or to adapters within fragments...
from your base activity, make your fragment manager static. assume this activity is called dashboard.
static FragmentManager support;
Don't forget to initialize this in onCreate.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layout_dashboard);
support = getSupportFragmentManager();
define your new fragment inside your adapter or fragment.
users_item_fragment dialog = new users_item_fragment();
//also, let's add some data...
Bundle args = new Bundle();
args.putString("device", devicesList.get(position));
use the following method to add the fragment easily wherever you would like
//pick an easily remembered tag
public void replace(Fragment fragment, String tag){
FragmentManager man = dashboard.support;
FragmentTransaction fragt = man.beginTransaction();
if(!fragment.isAdded()) {
dashboard.lastTag = dashboard.fragtag;//not needed, but helpful w/ backpresses
fragt.add(R.id.fragment_container, fragment, tag)
.hide(man.findFragmentByTag(fragtag)).commit();
dashboard.fragtag = dashboard.tag;//not needed, but helpful w/ backpresses
}
if(fragment.isAdded() && fragment.isHidden()) {
dashboard.lastTag = dashboard.fragtag;//not needed, but helpful w/ backpresses
fragt.show(fragment);
fragt.hide(man.findFragmentByTag(fragtag)).commit();
dashboard.fragtag = dashboard.tag;//not needed, but helpful w/ backpresses
}
}
To implement this with backpresses working correctly, add this in you onBackPress method of your main activity:
#Override
public void onBackPressed() {
FragmentManager man = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = man.beginTransaction();
fragmentTransaction.hide(getSupportFragmentManager().findFragmentByTag(fragtag))
.show(getSupportFragmentManager().findFragmentByTag(lastTag)).commit();
fragtag = lastTag;// holds the last fragment
}
}
It's easy to see the logic here and easy to manipulate back press events using this.

Activity to Fragment on button click

I have navigation bar on my app. Using that has created fragments. I added regular activities to the app and I have found how to go from a Fragment page to an activity page with using the onclick method.
By the click of a button I want to go from an activity page to a fragment page. How do I go about that?
Thank you

apply on click listner on the button and apply below code :-
Fragment fragment = new VehiclesFragment();
getSupportFragmentManager().beginTransaction().replace(R.id.container,fragment).commit();

If you want to close the current activity to go back to your Fragment-container Activity you may call the finish() method or onBackPressed() method (in case you're not overriding it).
If you want to bring a fragment to the current activity you must have a fragment container and attach it with:
getSupportFragmentManager().beginTransaction.add(R.id.container, fragment, TAG).addToBackStack().commit();

Try this code..
btn.setOnClickListener(new View.OnClickListener()){
#Override
public void onClick(View v) {
Intent intent = new Intent(getActivity(),FragmentTest.class);
getActivity().startActivity(intent);
}
});

If you want to move around in fragment then you have to be using either navigation bar clicks on tabs or use this from one fragment to another on a click of button .. like this
public void onNavigationDrawerItemSelected(int position) {
FragmentManager fragmentManager = getFragmentManager();
Fragment fragment = Fragment.instantiate(MainActivity.this, <name of the fragment>);
Bundle bundle = new Bundle();
bundle.putBoolean(ALL_EVENTS, true);
fragment.setArguments(bundle);
fragmentManager.beginTransaction().replace(R.id.container, fragment).commit();

Simply use this:
Intent(view.context, DestinationActivity::class.java).also {
view.context.startActivity(it)
}

Android How back button returns previous fragment?

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();
}
}

getFragmentByTag() never returns null

I've five fragments in my activity. On the click of fragment drawer list, I'm calling setFrament() method.
It removes the previous fragments from the activity, and adds the new one as per the requirement.
Here's my code for setFragment method.
protected void setFragment(final int position) {
// Remove currently active fragment
if (mActiveFragment != null) {
Fragment previous;
while ((previous = mFragmentManager
.findFragmentByTag(mActiveFragment.toString())) != null) {
mFragmentManager.beginTransaction().remove(previous).commit();
Log.e("in loop", "stuck");
}
}
// It's enum, generated according to position
FragmentType type = getFragmentType(position);
Fragment fragment = mFragmentManager.findFragmentByTag(type.toString());
if (fragment == null) {
fragment = createFragment(type);
}
mFragmentManager
.beginTransaction()
.replace(R.id.containerFrameLayout, fragment,
type.toString()).commit();
// Sets the current selected fragment checked in
// Drawer listview
mFragmentDrawerList.setItemChecked(position, true);
// set Actionbar title
getActionBar().setTitle(type + "");
mActiveFragment = type;
}
Here, while changing the fragment, it keeps prining "stuck" in while loop forever,
my question is,
why remove(Fragment) method doesn't remove the previous fragment from the activity ?

commit() is an asynchronous call that is only executed when the Android system regains control. The fragments won't be removed until some time after you leave the method.
If you want to remove the previous fragment (assuming there's only one), then you can add them to the backstack. Then you can call popBackStack(null, 0) which will pop everything on the back stack. The side catch though is pressing the "back" button will also pop the backstack if the user were to do that. You'll have to override the onBackPressed() and handle it yourself if you don't want that to happen.
EDIT:
One method would be to keep track of all IDs or TAGs and call remove on them individually.
LinkedList<Integer> fragmentIds = new LinkedList<Integer>();
/*** Add fragment to FragmentManager ***/
fragmentIds.add(/** ID of fragment */);
/** Removing all fragments from FragmentManager **/
FragmentManager fm = getFragmentManager();
FragmentTransaction transaction = fm.beginTransaction();
Fragment fragToRemove;
for(Integer id : fragmentIds)
{
fragToRemove = fm.findFragmentById(id);
transaction.remove(fragToRemove);
}
transaction.commit()
fragmentIds.clear();
However, you don't have to call remove on any of them so long as you use replace() method on the same container. replace() will pop the previous fragment and add in the new one. So long as the transaction isn't pushed to the backstack, the previous fragment is detached from the Activity and discarded.

how to know which fragment called another fragment?

I have this issue in Android. Consider three Fragments: A, B, C. C can be called from A or from B. Is there anyway to know from which fragment, C was called?
Edited
Ok guys I'm going to explain what I'm trying to do. Suppose I have this call: A calls B, B calls C.
When I press the back button in C It gets me to B, thats fine. But when I press the back button again, it takes me to C, instead of A.
This is my code:
#Override
public void onBackPressed() {
//this is the current fragment
Fragment fragmentActual = this.getSupportFragmentManager().findFragmentById(android.R.id.tabcontent);
String fragmentTag = fragmentoActual.getTag().toString();
//If I press the back button in C:
if(fragmentTag.equals("TAG C")){
Fragment removefragment = this.getSupportFragmentManager().findFragmentByTag("TAG B");
Fragment fragmentClient = this.getSupportFragmentManager().findFragmentByTag("TAG C");
//If Im NOT passing arguments to B, I know this is a new form
if(removefragment.getArguments()== null){
//I always pass arguments to fragment C, but just in case:
if(fragmentClient.getArguments()!= null){
Bundle mArguments = fragmentClient.getArguments();
//FRAGMENT B
FragmentB fragmentB = new FragmentB ();
fragment.setArguments(mArguments);
FragmentManager manager = this.getSupportFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
ft.addToBackStack(null);
ft.replace(android.R.id.tabcontent,fragmentB,"TAG B");
ft.commit();
}
}else{
super.onBackPressed();
}
}else{
super.onBackPressed();
}
}
Now I'm going to explain the code. Basically what it does is to replace fragment B, when fragment C is called. I do this, because I need to pass arguments to fragment B. But when I do the replacement, the "history" of the fragment B is lost, I mean when I press back button in B, I cant go back to fragment A (HERE IS WHY I WANTED TO KNOW IF I CAN KNOW WHO CALLS WHOM).
The firts time when I call fragment B, I dont pass arguments because is a blank form. But when I call to C, staying in B, I need to pass arguments to fragment B (when back button is pressed), so It can shows updated information.
Please if there something that is not clear, let me know so I can explain myself better.
Edited 2: This issue has something with this https://stackoverflow.com/questions/16703604/back-press-button-when-i-save-a-form-for-the-first-time-a-list-view-is-not-updat. Maybe it does my idea more clear.

The answer of Luksprog I think is the best: "You may want to tackle those issues. You always have the option of passing a Bundle with data to the newly created fragment mentioning who called it. Then using getArgument() in the fragment will know who called it.".
I haven't found another better way.

You can use the setTargetFragment method to set which was the parent fragment. Then you can use the method getTargetFragment to find out who called you.

What you are doing is transitioning between Fragments, call addToBackStack() as part of your FragmentTransaction:
i guess, This is what you need.
private final static String TAG_FRAGMENT = "TAG_FRAGMENT";
private void showFragment() {
final Myfragment fragment = new MyFragment();
final FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.fragment, fragment, TAG_FRAGMENT);
transaction.addToBackStack(null);
transaction.commit();
}
#Override
public void onBackPressed() {
final Myfragment fragment = (Myfragment) getSupportFragmentManager().findFragmentByTag(TAG_FRAGMENT);
if (fragment.allowBackPressed()) { // and then you define a method allowBackPressed with the logic to allow back pressed or not
super.onBackPressed();
}
}

You can use FragmentManager for creating a back stack of your fragments. You also have to work with Fragment Transactions first. Further informations see: http://developer.android.com/guide/components/fragments.html#Transactions