I'm currently utilizing the Navigation Drawer for my Android APP. In my first fragment, I've a fragment that loads data using Facebook's Graph API. Thus, when my App is first loaded, it first goes to the first fragment.
Then, I use the Navigation Drawer to click on another Fragment and view it.
And then finally, I reuse the Navigation Drawer to proceed back to the first Fragment and view it.
My issue that I'm facing is, how do I proceed to utilize the Fragment that has been created once instead of re-creating it whenever the Navigation Drawer Item is selected. My code for the switching of the fragments are as shown below.
private void displayView(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
fragment = new SelectionFragment();
break;
case 1:
fragment = new HomeFragment();
break;
case 2:
fragment = new PhotosFragment();
break;
case 3:
fragment = new CommunityFragment();
break;
case 4:
fragment = new PagesFragment();
break;
case 5:
fragment = new SplashFragment();
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame_container, fragment).commit();
// update selected item and title, then close the drawer
mDrawerList.setItemChecked(position, true);
mDrawerList.setSelection(position);
setTitle(navMenuTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
} else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
}
I noticed that there is indeed a "new" instance of the Fragment every time whenever the option is selected. How do I go about implementing the logic of creating the Fragment instance ONCE and reusing it, so that I do not have to continuously load the Fragment over and over again.
To anyone who encounters the same issue with me,I've managed to find a solution.
In the container frame,I've to define specific fragment views that I'll be utilizing as shown below.
In each Fragment view,I've to "link" it with the actual Fragment itself as shown below via the "android:name" attribute.Do take note of the the path to the Fragment,example for in my case it's com.example.confesssionsrp.SelectionFragment.
<fragment
android:id="#+id/selectionFragment"
android:name="com.example.confessionsrp.SelectionFragment"
android:layout_width="match_parent"
android:layout_height="match_parent" />
In the the MainActivity(or the Activity where we're viewing the fragments),create variables for each of the Fragments as shown below.
Following that,in the Oncreate of the MainActivity(or your specific Activity),initialize the various fragments as shown below.
Proceed onto creating a new Method called "ShowFragment" as shown below.
private void showFragment(int fragmentIndex, boolean addToBackStack) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction transaction = fm.beginTransaction();
for (int i = 0; i < fragments.length; i++) {
if (i == fragmentIndex) {
transaction.show(fragments[i]);
if (Session.getActiveSession().isClosed()) {
mDrawerLayout
.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
}
} else {
transaction.hide(fragments[i]);
}
}
if (addToBackStack) {
transaction.addToBackStack(null);
}
transaction.commit();
}
From then on in the switching of the fragments,manually call upon the "ShowFragment" method with the selected Fragment as shown below.
Doing all of this overall,will not reset the Fragment each time we view it,and therefore is the solution to the answer.Thank you for anyone who has helped me so far :)!
I am using the following code:
#Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
FragmentManager fragmentManager = getFragmentManager();
if(position==0){// selection of tabs content
fragmentManager
.beginTransaction()
.replace(R.id.container,
SimulatorFragment.newInstance(position + 1)).commit();
}else if(position==1){
fragmentManager
.beginTransaction()
.replace(R.id.container,
HudFragment.newInstance(position + 1)).commit();
}else if(position==2){
// Display the fragment as the main content.
fragmentManager
.beginTransaction()
.replace(R.id.container,
SettingsBasicFragment.newInstance(position +1)).commit();
}else{
}
}
You can replace by a new instance the first time and store the fragment, if it is not null, then replace by the stored fragment.
The activity must implement NavigationDrawerFragment.NavigationDrawerCallbacks
The fragment constructor and newInstance methods look like this:
public final class HudFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section number.
* #param simulation
*/
public static HudFragment newInstance(int sectionNumber) {
HudFragment fragment = new HudFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public HudFragment() {
}
To switch fragments by code I use this method inside the NavigationDrawerFragment:
/**
* Select a different section
* #param position
*/
public void select(int position){
selectItem(position);
}
private void selectItem(int position) {
mCurrentSelectedPosition = position;
if (mDrawerListView != null) {
mDrawerListView.setItemChecked(position, true);
}
if (mDrawerLayout != null) {
mDrawerLayout.closeDrawer(mFragmentContainerView);
}
if (mCallbacks != null) {
mCallbacks.onNavigationDrawerItemSelected(position);
}
}
The second option is to start with the example of navigationDrawer that Android SDK offers. I selected that template of activity when creating the project and almost all the code of my previous answer is produced automatically.
If you want to keep the fragments after device rotation or similars it is a different thing, you need then to retain the fragments. If not, you just need to save the new instance of the fragment in a variable and check if it is null to create a new one or use the old one.
In case someone want's a different approach to this: you could find the fragment on the stack:
// check if this fragment is on the backstack to avoid creating a new one
Fragment foundFragment = fragmentManager.findFragmentByTag("unique_fragment_tag");
if (foundFragment != null) {
fragmentManager.popBackStackImmediate("unique_fragment_tag", 0);
return;
}
Related
I am adding a BottomNavigationView with three fragments to my app.
Everything works correctly, except one thing.
In the first fragment, there is an EditText view, in the second a ListView and in the third one some texts and images loaded from a JSON hosted in the server.
This is my code:
bottomNavigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.menu_dash:
fragment = new frg_dash();
break;
case R.id.menu_list:
fragment = new frg_list();
break;
case R.id.menu_info:
fragment = new frg_info();
break;
}
final FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(R.id.contenedor_principal, fragment).commit();
return true;
}
});
The problem is that every time I go from one fragment to another using the bottomNavigationView buttons, the Fragment starts all its execution again.
The result I'm looking for is that if the user in the second fragment is, for example, in the middle of the ListView, it goes to the third fragment and returns again, the ListView continues where it was.
Or if you press the button of the third Fragment in the bottomNavigationView, do not load the data again from the server.
I guess the problem is that when you click on a bottomNavigationView button, the fragment is created again:
... switch (id) {
case R.id.menu_dash:
fragment = new frg_dash();
break; ...
But it's just a guess. I suppose it can be controlled with the onCreate, onActivityCreated and onCreateView methods, but again, they are just my assumptions.
I've tried it with the hide () and show () parameters of the fragments, but without success ... or I'm not applying it well
I greatly appreciate the help in advance.
EDIT
This is my example currently with all the parts related to the answer:
public void replaceFragment(Fragment fragment, #Nullable Bundle bundle, boolean popBackStack, boolean findInStack) {
Log.v("2134", "Dentro");
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
String tag = fragment.getClass().getName();
Log.v("2134", "tag:" + tag);
Fragment parentFragment;
if (findInStack && fm.findFragmentByTag(tag) != null) {
parentFragment = fm.findFragmentByTag(tag);
} else {
parentFragment = fragment;
}
// if user passes the #bundle in not null, then can be added to the fragment
if (bundle != null) {
parentFragment.setArguments(bundle);
} else {
parentFragment.setArguments(null);
}
// this is for the very first fragment not to be added into the back stack.
if (popBackStack) {
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
} else {
ft.addToBackStack(parentFragment.getClass().getName() + "");
}
ft.replace(R.id.contenedor_principal, parentFragment, tag);
ft.commit();
fm.executePendingTransactions();
}
...
bottomNavigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.menu_panel:
fragment = new frg_panel();
break;
case R.id.menu_promos:
fragment = new frg_promociones();
break;
case R.id.menu_catalogo:
fragment = new frg_catalogo();
break;
}
replaceFragment(fragment, null, true, true);
return true;
}
});
Use this code to open your fragment. Your fragment will not create every time. It will get same fragment from stack if exist.
/**
* replace or add fragment to the container
*
* #param fragment pass android.support.v4.app.Fragment
* #param bundle pass your extra bundle if any
* #param popBackStack if true it will clear back stack
* #param findInStack if true it will load old fragment if found
*/
public void replaceFragment(Fragment fragment, #Nullable Bundle bundle, boolean popBackStack, boolean findInStack) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
String tag = fragment.getClass().getName();
Fragment parentFragment;
if (findInStack && fm.findFragmentByTag(tag) != null) {
parentFragment = fm.findFragmentByTag(tag);
} else {
parentFragment = fragment;
}
// if user passes the #bundle in not null, then can be added to the fragment
if (bundle != null)
parentFragment.setArguments(bundle);
else parentFragment.setArguments(null);
// this is for the very first fragment not to be added into the back stack.
if (popBackStack) {
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
} else {
ft.addToBackStack(parentFragment.getClass().getName() + "");
}
ft.replace(R.id.contenedor_principal, parentFragment, tag);
ft.commit();
fm.executePendingTransactions();
}
use it like
Update :
If your fragment is home or dashboard fragment then
Fragment f = new YourFragment();
replaceFragment(f, null, true, true);
Otherwise
Fragment f = new YourFragment();
replaceFragment(f, null, false, true);
Important This code is not replacement of saving all states or variables in fragment. This code will useful because it will not create fragment instance again.
For saving all states and variables in fragment for future use see this answer
I have the slider menu displayview method as:
private void displayView(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
fragment = new HomeFragment();
FragmentManager fm = getSupportFragmentManager();
String tag = fragment.getTag(); // instance method of a to get a tag
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.frame_container, fragment, tag);
ft.addToBackStack(tag);
ft.commit();
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame_container, fragment).commit();
// update selected item and title, then close the drawer
drawerListView.setItemChecked(position, true);
drawerListView.setSelection(position);
setTitle(navMenuTitles[position]);
drawer.closeDrawer(drawerListView);
} else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
}
I have a fragment called home_fragment whose code behind is HomeFragment.java
When I click on this fragment first it works fine, but on clicking next from the siding menu at index 0 I get an error as:
Attempt to write to field 'int android.support.v4.app.Fragment.mNextAnim' on a null object reference
What am I doing wrong? Thanks.
This is where I'm having error:
case OP_REMOVE: {
Fragment f = op.fragment;
f.mNextAnim = exitAnim;
mManager.removeFragment(f, transition, transitionStyle);
} break;
This code is present in BackStackRecord.java
You shouldn't be calling container.removeAllViewsInLayout().
The FragmentManager will handle all the view manipulation on the container when you call FragmentTransaction.replace(), including removing the current fragment view. You are probably getting an error because the FragmentManager expects a fragment's view to be in the container, but you've removed it.
All you need is this:
private void displayView(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
fragment = new HomeFragment();
break;
case 1:
// set fragment to other nav target
fragment = ...
break;
.
.
.
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame_container, fragment).commit();
// update selected item and title, then close the drawer
drawerListView.setItemChecked(position, true);
drawerListView.setSelection(position);
setTitle(navMenuTitles[position]);
drawer.closeDrawer(drawerListView);
} else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
}
Also I noticed you are using getFragmentManager(). Please check your class imports and make sure that you have the right call.
If HomeFragment extends android.app.Fragment, use getFragmentManager().
If HomeFragment extends android.support.v4.app.Fragment, use getSupportFragmentManager().
okay i know there are other questions that on first glance make this one look like a duplicate, but none of these answers work in my case,
What i want is the first fragment displayed to be like a Main Activity in respect to how the back button works, i need whichever fragment i choose from my navigation drawer to go back to the first fragment when the back button is pressed then a user would quit the app by pressing it again.
So ive tried using addToBackStack and when i move to another fragment if i press the back button it comes back to my first fragment (exactly as i want) but pressing the back button again leaves me with a white screen (i wonder if this is due to the transaction animation im using which ive included below) so to get around this i tried overriding the back button and throwing in a call to finish(); but this causes whichever fragment im in to finish instead of going back to the first fragment, ive tried a handful of workarounds from the above mentioned link and many others but cannot find a decent fix any suggestions?
here is my Main Activity displayView
private void displayView(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
fragment = new FirstFragment();
break;
case 1:
fragment = new glideFrag();
break;
case 2:
fragment = new secondGlideFrag();
break;
case 3:
fragment = new thirdGlideFrag();
break;
case 4:
fragment = new forthGlideFrag();
break;
case 5:
fragment = new lgFrag();
break;
case 6:
fragment = new cyanFrag();
break;
case 7:
fragment = new sonyFrag();
break;
case 8:
fragment = new SecondFragment();
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.setCustomAnimations(R.anim.enter,R.anim.exit,R.anim.pop_enter,R.anim.pop_exit);
//fragmentManager.beginTransaction()
fragmentTransaction.replace(R.id.frame_container, fragment).addToBackStack("first Fragment").commit();
// update selected item and title, then close the drawer
mDrawerList.setItemChecked(position, true);
mDrawerList.setSelection(position);
setTitle(navMenuTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
} else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
i found this that looks like a great way around it
private boolean popNext = false;
if(popNext){
if(position == INITIAL_POSITION){
onBackPressed();
mDrawerLayout.closeDrawer(mDrawerList);
popNext = false;
return;
}
getSupportFragmentManager().popBackStackImmediate();
}
else{
if(position == INITIAL_POSITION){
mDrawerLayout.closeDrawer(mDrawerList);
return;
}
popNext=true;
}
but im still fairly new to android and im not sure what to set INITIAL_POSITION to, I tried
private static final INITIAL_POSITION = 0;
but without any luck
When adding the initial fragment, you must not add it to the back stack.
You must only do it for the next ones. When the back stack will be empty, the Activity will just finish.
Edit: Here is an explanation of the problem so you can figure out how to fix it:
Each time you add a fragment transaction to the back stack, you allow the user to revert it by pressing the back button and the Activity will return to the state it was before the transaction. If the initial fragment is added to the back stack, then when the user press back, the screen becomes blank, because there was nothing displayed before you added the initial fragment. That's why the initial fragment transaction which adds the first visible fragment to your Activity must not be added to the back stack. Usually you initialize the initial fragment like this:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState == null) {
Fragment fragment = new FirstFragment();
getSupportFragmentManager().beginTransaction()
.add(R.id.frame_container, fragment)
.commit();
}
}
BladeCoders answer was more trying to tell me how the backstack works rather than answering my question, i ended up not adding any fragments to the back stack, .addToBackStack(null), and overriding back button in MainActivity, feels like a little bit of a hack but works perfectly
#Override
public void onBackPressed() {
FragmentManager fragmentManager = getSupportFragmentManager();
if (fragmentManager.getBackStackEntryCount() < 1){
Fragment fragment = new FirstFragment();
FragmentTransaction fragmentTransaction =
getSupportFragmentManager().beginTransaction();
fragmentTransaction.setCustomAnimations(R.anim.enter, R.anim.exit,
R.anim.pop_enter, R.anim.pop_exit);
getSupportActionBar().setTitle(mDrawerTitle);
fragmentTransaction.replace(R.id.frame_container,
fragment).addToBackStack("first").commit();
}else{
finish();
}
}
You can do it even with out backstack its just my point of view to simplify so that it can help some one.
#Override
public void onBackPressed(){
Fragment f = getSupportFragmentManager().findFragmentById(R.id.container_body);
if(f.getClass().getName().equals(HomeFragment.class.getName())){ // here HomeFragment.class.getName() means from which faragment you actually want to exit
finish();
}else{
displayView(0); //were you want to go when back button is pressed
}
}
private void displayView(int position) {
Fragment fragment = null;
String title = getString(R.string.app_name);
switch (position) {
case 0:
fragment = new HomeFragment();
title = getString(R.string.app_name);
break;
case 1:
fragment = new OffersFragment();
title = getString(R.string.nav_item_offers);
break;
case 2:
fragment = new NotificationFragment();
title = getString(R.string.nav_item_notifications);
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.container_body, fragment);
fragmentTransaction.commit();
// set the toolbar title
getSupportActionBar().setTitle(title);
}
}
I'm working on an android application, that uses a navigation drawer to switch between two fragments. However, each time I switch, the fragment is completely recreated.
Here is the code from my main activity.
/* The click listener for ListView in the navigation drawer */
private class DrawerItemClickListener implements ListView.OnItemClickListener {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
selectItem(position);
}
}
private void selectItem(int position) {
android.support.v4.app.Fragment fragment;
String tag;
android.support.v4.app.FragmentManager; fragmentManager = getSupportFragmentManager();
switch(position) {
case 0:
if(fragmentManager.findFragmentByTag("one") != null) {
fragment = fragmentManager.findFragmentByTag("one");
} else {
fragment = new OneFragment();
}
tag = "one";
break;
case 1:
if(fragmentManager.findFragmentByTag("two") != null) {
fragment = fragmentManager.findFragmentByTag("two");
} else {
fragment = new TwoFragment();
}
tag = "two";
break;
}
fragment.setRetainInstance(true);
fragmentManager.beginTransaction().replace(R.id.container, fragment, tag).commit();
// update selected item and title, then close the drawer
mDrawerList.setItemChecked(position, true);
setTitle(mNavTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
I've set up some debug logging, and every time selectItem is called, one fragment is destroyed, while the other is created.
Is there any way to prevent the fragments from being recreated, and just reuse them instead?
After #meredrica pointed out that replace() destroys the fragments, I went back through the FragmentManager documentation. This is the solution I've come up with, that seems to be working.
/* The click listener for ListView in the navigation drawer */
private class DrawerItemClickListener implements ListView.OnItemClickListener {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
selectItem(position);
}
}
private void selectItem(int position) {
android.support.v4.app.FragmentManager; fragmentManager = getSupportFragmentManager();
switch(position) {
case 0:
if(fragmentManager.findFragmentByTag("one") != null) {
//if the fragment exists, show it.
fragmentManager.beginTransaction().show(fragmentManager.findFragmentByTag("one")).commit();
} else {
//if the fragment does not exist, add it to fragment manager.
fragmentManager.beginTransaction().add(R.id.container, new OneFragment(), "one").commit();
}
if(fragmentManager.findFragmentByTag("two") != null){
//if the other fragment is visible, hide it.
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("two")).commit();
}
break;
case 1:
if(fragmentManager.findFragmentByTag("two") != null) {
//if the fragment exists, show it.
fragmentManager.beginTransaction().show(fragmentManager.findFragmentByTag("two")).commit();
} else {
//if the fragment does not exist, add it to fragment manager.
fragmentManager.beginTransaction().add(R.id.container, new TwoFragment(), "two").commit();
}
if(fragmentManager.findFragmentByTag("one") != null){
//if the other fragment is visible, hide it.
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("one")).commit();
}
break;
}
// update selected item and title, then close the drawer
mDrawerList.setItemChecked(position, true);
setTitle(mNavTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
I also added this bit, but I'm not sure if it's necessary or not.
#Override
public void onDestroy() {
super.onDestroy();
FragmentManager fragmentManager = getSupportFragmentManager();
if(fragmentManager.findFragmentByTag("one") != null){
fragmentManager.beginTransaction().remove(fragmentManager.findFragmentByTag("one")).commit();
}
if(fragmentManager.findFragmentByTag("two") != null){
fragmentManager.beginTransaction().remove(fragmentManager.findFragmentByTag("two")).commit();
}
}
Use the attach/detach method with tags:
Detach will destroy the view hirachy but keeps the state, like if on the backstack; this will let the "not-visible" fragment have a smaller memory footprint. But mind you that you need to correctly implement the fragment lifecycle (which you should do in the first place)
Detach the given fragment from the UI. This is the same state as when it is put on the back stack: the fragment is removed from the UI, however its state is still being actively managed by the fragment manager. When going into this state its view hierarchy is destroyed.
The first time you add the fragment
FragmentTransaction t = getSupportFragmentManager().beginTransaction();
t.add(android.R.id.content, new MyFragment(),MyFragment.class.getSimpleName());
t.commit();
then you detach it
FragmentTransaction t = getSupportFragmentManager().beginTransaction();
t.detach(MyFragment.class.getSimpleName());
t.commit();
and attach it again if switched back, state will be kept
FragmentTransaction t = getSupportFragmentManager().beginTransaction();
t.attach(getSupportFragmentManager().findFragmentByTag(MyFragment.class.getSimpleName()));
t.commit();
But you always have to check if the fragment was added yet, if not then add it, else just attach it:
if (getSupportFragmentManager().findFragmentByTag(MyFragment.class.getSimpleName()) == null) {
FragmentTransaction t = getSupportFragmentManager().beginTransaction();
t.add(android.R.id.content, new MyFragment(), MyFragment.class.getSimpleName());
t.commit();
} else {
FragmentTransaction t = getSupportFragmentManager().beginTransaction();
t.attach(getSupportFragmentManager().findFragmentByTag(MyFragment.class.getSimpleName()));
t.commit();
}
The replace method destroys your fragments. One workaround is to set them to Visibility.GONE, another (less easy) method is to hold them in a variable. If you do that, make sure you don't leak memory left and right.
I did this before like this:
if (mPrevFrag != fragment) {
// Change
FragmentTransaction ft = fragmentManager.beginTransaction();
if (mPrevFrag != null){
ft.hide(mPrevFrag);
}
ft.show(fragment);
ft.commit();
mPrevFrag = fragment;
}
(you will need to track your pervious fragment in this solution)
I guess you can not directly manipulate the lifecycle mechanisms of your Fragments. The very fact that you can findFragmentByTag is not very bad. It means that the Fragment object is not recreated fully, if it is already commited. The existing Fragment just passes all the lifecycle steps each Fragment has - that means that only UI is "recreated".
It is a very convenient and useful memory management strategy - and appropriate, in most cases. Fragment which is gone, has the resources which have to be utilized in order to de-allocate memory.
If you just cease using this strategy, the memory usage of your application could increase badly.
Nonetheless, there are retained fragments, which lifecycle is a bit different and do not correspond to the Activity they are attached to. Typically, they are used to retain some things you want to save, for example, to manage configuration changes
However, the fragment [re]creation strategy depends on the context - that is, what you would like to solve, and what are the trade-offs that you are willing to accept.
Just find the current fragment calling getFragmentById("id of your container") and then hide it and show needed fragment.
private void openFragment(Fragment fragment, String tag) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Fragment existingFragment = fragmentManager.findFragmentByTag(tag);
if (existingFragment != null) {
Fragment currentFragment = fragmentManager.findFragmentById(R.id.container);
fragmentTransaction.hide(currentFragment);
fragmentTransaction.show(existingFragment);
}
else {
fragmentTransaction.add(R.id.container, fragment, tag);
}
fragmentTransaction.commit();
}
Same idea as Tester101 but this is what I ended up using.
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Fragment oldFragment = fragmentManager.findFragmentByTag( "" + m_lastDrawerSelectPosition );
if ( oldFragment != null )
fragmentTransaction.hide( oldFragment );
Fragment newFragment = fragmentManager.findFragmentByTag( "" + position );
if ( newFragment == null )
{
newFragment = getFragment( position );
fragmentTransaction.add( R.id.home_content_frame, newFragment, "" + position );
}
fragmentTransaction.show( newFragment );
fragmentTransaction.commit();
Hide easily in kotlin using extensions:
fun FragmentManager.present(newFragment: Fragment, lastFragment: Fragment? = null, containerId: Int) {
if (lastFragment == newFragment) return
val transaction = beginTransaction()
if (lastFragment != null && findFragmentByTag(lastFragment.getTagg()) != null) {
transaction.hide(lastFragment)
}
val existingFragment = findFragmentByTag(newFragment.getTagg())
if (existingFragment != null) {
transaction.show(existingFragment).commit()
} else {
transaction.add(containerId, newFragment, newFragment.getTagg()).commit()
}
}
fun Fragment.getTagg(): String = this::class.java.simpleName
Usage
supportFragmentManager.present(fragment, lastFragment, R.id.fragmentPlaceHolder)
lastFragment = fragment
Here's what I'm using for a simple 2 fragment case in Kotlin:
private val advancedHome = HomeAdvancedFragment()
private val basicHome = HomeBasicFragment()
override fun onCreate(savedInstanceState: Bundle?) {
...
// Attach both fragments and hide one so we can swap out easily later
supportFragmentManager.commit {
setReorderingAllowed(true)
add(R.id.fragment_container_view, basicHome)
add(R.id.fragment_container_view, advancedHome)
hide(basicHome)
}
binding.displayModeToggle.onStateChanged {
when (it) {
0 -> swapFragments(advancedHome, basicHome)
1 -> swapFragments(basicHome, advancedHome)
}
}
...
}
With this FragmentActivity extension:
fun FragmentActivity.swapFragments(show: Fragment, hide: Fragment) {
supportFragmentManager.commit {
show(show)
hide(hide)
}
}
How about playing with the Visible attribute?
this is a little late response.
if you're using view pager for fragments, set the off screen page limit of the fragment to the number of fragments created.
mViewPager.setOffscreenPageLimit(3); // number of fragments here is 3
I am using ActionBarSherlock and applying this pattern for the tab navigation that I found on android developer site. It's working pretty good but I also want to able to switch between NAVIGATION_MODE_TABS and NAVIGATION_MODE_LIST preserving the association between tabs and the fragments.
The pattern I mentioned above is pretty good for preserving a generic code. So I add listeners to my tabs and associate them with specific fragments like this:
bar.addTab(bar.newTab()
.setText("MyFragment")
.setTabListener(new TabListener<SomeFragment>(this, "myfargment", SomeFragment.class)));
and instantiate the fragment when the associated tab is clicked with the help of generics:
public void onTabSelected(Tab tab, FragmentTransaction ft) {
if (mFragment == null) {
mFragment = Fragment.instantiate(mActivity, mClass.getName(), mArgs);
ft.add(android.R.id.content, mFragment, mTag);
} else {
ft.attach(mFragment);
}
}
My question is how can I achieve a similar way while navigating between my fragments with the list navigation mode. I couldn't find a similar way since the OnNavigationListener for the list on the ActionBar works for the whole list instead of per item basis like the tablistener.
or do I have to do something like this:
#Override
public boolean onNavigationItemSelected(int itemPosition, long itemId) {
switch (itemPosition) {
case 0:
//Replace the current fragment with FragmentA
break;
case 1:
//Replace the current fragment with FragmentB
break;
case 2:
//Replace the current fragment with FragmentC
break;
default:
break;
}
return true;
}
EDIT:
I have noticed an interesting behaviour:
While the navigation mode is set to NAVIGATION_MODE_TABS if I put my phone in landscape mode it converts the tabs to a list and preservers the association between the fragments and the list items(which were tab items before) how can I achieve this result on demand rather than on orientation change?
I dont think its possible if you are in tab mode to manually set to a list navigation. I have the list navigation set for one of my applications when it falls below the "Large" bucket. This is how I am using the navigation listener:
OnNavigationListener mNavigationListener = new OnNavigationListener()
{
int mLastPosition = -1;
#Override
public boolean onNavigationItemSelected(int itemPosition, long itemId)
{
String selectedTag = mFragmentNames.get(itemPosition);
FragmentManager fm = getSupportFragmentManager();
Fragment fragment = fm.findFragmentByTag(selectedTag);
FragmentTransaction ft = fm.beginTransaction();
/** Used to avoid the same fragment being reattached. */
if(mLastPosition != itemPosition)
{
/** Means there was a previous fragment attached. */
if(mLastPosition != -1)
{
Fragment lastFragment = fm.findFragmentByTag(mFragmentNames.get(mLastPosition));
if(lastFragment != null)
ft.remove(lastFragment);
}
if(fragment == null)
{
/** The fragment is being added for the first time. */
fragment = Fragment.instantiate(HomeActivity.this, selectedTag);
ft.add(R.id.rootLayout, fragment, selectedTag);
ft.commit();
} else
{
ft.attach(fragment);
ft.commit();
}
}
/**
* The newly attached fragment will be the last position if changed.
*/
mLastPosition = itemPosition;
return true;
}
};
The variable mFragmentNames is a HashMap that maps a integer position to a fragment name ex. "com.android.myproject.MyFragment"
I hope this helps.