In my android application, a fragment will be added to the activity by a certain action (for example, the action bar menu).
This is the code I add the fragment:
case R.id.action_add_box:
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.place, BoxEditFragment.newInstance(null, null));
ft.addToBackStack(null);
ft.commit();
break;
Now once the user hit the action menu with id action_add_box two times, then he have to hit the back two times to close the fragment which is not expected.
Is it possible to avoid this?
For example, once user hit the action menu, do nothing if the fragment have been already visible to the user?
And one more question, there are some EditTexts in the fragment, once user complete, I will submit the data and close the fragment, however user may need to open the fragment again, and I want to keep the value of the EditText as last entered by user. Now I save the values when the fragment are detached and reset the value when created using the savedInstanceState.
Also create a new instance of the fragment for each action command is a waste of memory, I wonder if I can use only one fragment instance, then I may not need to save/reset the values manually?
you can use singleton parttern to keep one instance of fragment for eg:
public class MyFragment extends Fragment{
public static MyFragment oneInstance = null ;
private MyFragment(){
super();
}
public static MyFragment getInstance(){
if (oneInstance == null ){
synchronized (MyFragment.class){
if ( oneInstance == null ){
oneInstance = new MyFragment();
}
}
return oneInstance ;
}
}
the above code is also thread safe
MyFragment frag= (MyFragment )getFragmentManager().findFragmentById(R.id.your_fragment_layout);
if(frag == null){
// fragment is not visible
}else{
// fragment is visible
}
Related
I am using NavigationDrawer in my application and each menu item in drawer is a fragment.Whenever user chooses a menu item I replace the current fragment in the main container with the requested one but it recreates the fragment every-time, so i updated my code to reuse the existing fragments instead of creating them again and again as content of fragments remain same. My updated code to show fragment is :
public void showTabFragment() {
TabFragment Tf = (TabFragment) mFragmentManager.findFragmentByTag(Constants.TAB_FRAGMENT);
mFragmentTransaction = mFragmentManager.beginTransaction();
if (Tf != null) {
mFragmentTransaction.replace(R.id.containerView, Tf, Constants.TAB_FRAGMENT);
} else {
mFragmentTransaction.replace(R.id.containerView, new TabFragment(), Constants.TAB_FRAGMENT);
}
mFragmentTransaction.commit();
}
In above code I am trying to get fragments by Tag but it always returns null and executes the else case(new fragment).Could someone please guide me what am I doing wrong in my code?
I guess the code you've shown is for one of your menu fragment? If that's the case, what is probably happening is every time you open a menu item, the container is replaced with the new fragment(say, Fragment B) with its new tag(say, TAG 'B'). So, when you try to open the previous fragment(say, Fragment A) using it's tag(TAG 'A'), it won't be there, because that's what you replaced.
One possible solution is to hold references to the fragment as they are created, in, say a hashmap, and reuse them instead.
private HashMap<String, Fragment> menuFragments = new HashMap<>();
public void showMenu(String fragmentID)
{
MenuFragment fragment = menuFragments.get(fragmentID);
if(fragment == null)
{
fragment = new MenuFragment(); //Create the respective menu fragment based on the ID.
menuFragments.put(fragmentID, fragment);
}
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.containerView, fragment, fragmentID);
transaction.commit();
}
I started a new project using tabbed activity of Android Studio. It created an activity with ViewPager and 3 fragments = fragment1, fragment2 and fragment3.
I changed fragment1 to have a listView and a TextView, that I initialize when the fragment is created. The data in the listView is read from an SQL database.
When the application starts, fragment1 is displayed and the listView shows the data read from SQL.
When I swipe from fragment1 to fragment2 and back, fragment1 shows the listview properly. However, when I swipe to fragment3 and back to fragment1 the listview data is lost and I get a blank screen, although the textview shows properly.
When I change the application to have only 2 fragments it does not happen and I can swipe from fragment1 to fragment2 and back many times without any loss of data. The moment I add the 3rd fragment, the data is lost on first swipe to fragment3, but is not lost if I swipe between fragment 1 and fragment2 only.
Any idea why is it happening?
This is happening because by default ViewPager has a function named setOffscreenPageLimit(int i). This tells ViewPager how many of the Fragments need to store in memory. By default it is '2'. So when you swipe to Fragment 2 from Fragment 1 it will still keep Fragment 1 in memory and won't destroy it from memory. But when you swipe to Fragment 3 it will have Fragment 2 and Fragment 3 in memory so it will remove Fragment 1.
That's why when you come back to your first Fragment it have lost its views or data.
Try to use
mViewPager.setOffscreenPageLimit(your total fragment count +1);
Or much better solution
Do not replace your fragment when you swipe in ViewPager. Push it to the backstack and when you comeback to it, Check for the backstack and if fragment is there then just Pop it and display it.
Here is the code:
public void pushFragments(String tag, Fragment fragment) {
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
if (manager.findFragmentByTag(tag) == null) {
ft.add(R.id.frame_container, fragment, tag);
}
String tagOne="com........Frag_one"; //your fragment class name
String tagTwo="com........Frag_two";
String tagThree="com........Frag_three";
String tagFour="com........Frag_profile";
Fragment fragmentOne = manager.findFragmentByTag(tagOne);
Fragment fragmentTwo = manager.findFragmentByTag(tagTwo);
Fragment fragmentThree = manager.findFragmentByTag(tagThree);
Fragment fragmentFour = manager.findFragmentByTag(tagFour);
manager.executePendingTransactions();
// Hide all Fragment
if (fragmentOne != null) {
ft.hide(fragmentOne);
}
if (fragmentTwo != null) {
ft.hide(fragmentTwo);
}
if (fragmentThree != null) {
ft.hide(fragmentThree);
}
if (fragmentFour != null) {
ft.hide(fragmentFour);
}
// Show current Fragment
if (tag.equals(tagOne)) {
if (fragmentOne != null) {
ft.show(fragmentOne);
}
}
if (tag.equals(tagTwo)) {
if (fragmentTwo != null) {
ft.show(fragmentTwo);
}
}
if (tag.equals(tagThree)) {
if (fragmentThree != null) {
ft.show(fragmentThree);
}
}
if (tag.equals(tagFour)) {
if (fragmentFour != null) {
ft.show(fragmentFour);
}
}
ft.commit();
}
And Here is how you call it:
Fragment fragment = new Frag_one();
pushFragments(fragment.getClass().getName(),fragment);
Issue solved. The problem is due to the adapter keeping 3 fragments in memory, as pointed by #Daniel Nugent. The data in the pages is loaded from DB so that when the view is recreated, when fragments are destroyed and recreated as the user swipes, the listview adapter has lost the data, and one has to repopulate it. The problem does not appear on simple examples because usually the data presented is static and is loaded in the onCreateView method.
I have this activity where I run an asynctask that gathers a series of data. This data can be represented in several ways, for the sake of simplicity let's say there's two ways. I want the user to be able to switch between these two representations (listview and graphical view).
So I created a FragmentActivity with my ListFragment and my GraphicFragment.
How do you switch between these two so that user can go back and forth? I tried using replace but then the previous fragment gets destroyed which is not of my interest since its reference has the data passed by my Activity. (i.e. I don't want to recreate the fragment each times the user switches between views).
I also tried hiding and showing but I can't get it to work, one of the fragments is not showing.
Also, when I rotate I guess the fragments get destroyed because I get a nullpointerexception when trying to access them.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_layout);
pBar = (ProgressBar) findViewById(R.id.analyzingProgress);
// However, if we're being restored from a previous state, then don't
// create the fragment again (please)
if (savedInstanceState == null) {
firstFragment = new DirListFragment();
secondFragment = new GraphViewFragment();
getSupportFragmentManager().beginTransaction().add(R.id.fragment_container, secondFragment).commit();
fragments= new ArrayList<IFragment>();
fragments.add(firstFragment);
fragments.add(secondFragment);
}
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
if(item.getItemId() == R.id.listView){
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
/*transaction.hide(secondFragment);
transaction.show(firstFragment);*/
transaction.replace(R.id.fragment_container, firstFragment);
transaction.addToBackStack(null);
transaction.commit();
}
else if(item.getItemId() == R.id.graph){
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
/*transaction.hide(firstFragment);
transaction.show(secondFragment);*/
transaction.replace(R.id.fragment_container, secondFragment);
transaction.addToBackStack(null);
transaction.commit();
}
return true;
}
The problem comes when I try to access the fragment fields to update their data:
for(IMyFragment frag: fragments){
frag.updateData(data);
}
I get a NullPointerException after rotating the screen.
Also when switching fragmenents, their data is not updated (i.e. I start with list fragment, it's showing the proper data, then switch to graphic, no data is shown, switch back to list, no data again.)
If the fields are null when using setRetainInstance(true);, then you are recreating them (the fragments) in your activity. Make sure you are setting something in onSaveInstanceState() in your activity so in onCreate(), savedInstanceState will not be null, it can even be an empty bundle or useless variable, ex:
#Override
public void onSaveInstanceState(Bundle outstate){
super.onSaveInstanceState(outstate);
outstate.putBoolean("stateChanged", true);
}
Just make sure you call super before adding your arguments.
On another note, I personally have never stored my fragments in an array. I use a FrameLayout as a fragment container in my activities, just like you, and if I need to update something I just call: getSupportFragmentManager().findFragmentById(R.id.fragment_container).setWhatINeed(); This way I always get the visible fragment.
Let me know how the update goes and I'll update this post with any information I can.
I have an application running a single activity with multiple (2) fragments at a given time. I've got a fragment on the left which functions as a menu for which fragment to
display on the right hand side.
As an example lets say the menu consists of different sports; Football, Basketball, Baseball, Skiing, etc. When the user selects a sport, a fragment with details on the specific sport is displayed to the right.
I've set up my app to display two fragments at once in layout-large and layout-small-landscape. In layout-small-portrait however, only one fragment is displayed at a given time.
Imagine this; a user is browsing the app in layout-small-landscape (two fragments at a time) and selects a sport, Football. Shortly after he selects Basketball. If he now chooses to rotate into layout-small-portrait (one fragment at a time) I want the following to happen:
The Basketball fragment should be visible, but if he presses the back button, he should return to the menu and not to the Football fragment (!) which by default is the previous fragment in the back stack.
I have currently solved this like the following:
....
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// static fragments
if(menuFragment == null) menuFragment = new MenuFragment();
if(baseFragment == null) baseFragment = new TimerFragment(); // default content fragment
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
// Determine what layout we're in..
if(app().getLayoutBehavior(this) == LayoutBehavior.SINGLE_FRAGMENT) {
// We are currently in single fragment mode
if(savedInstanceState != null) {
if(!rotateFromSingleToDual) {
// We just changed orientation from dual fragments to single fragment!
// Clear the entire fragment back stack
for(int i=0;i<getSupportFragmentManager().getBackStackEntryCount();i++) {
getSupportFragmentManager().popBackStack();
}
ft.replace(R.id.fragmentOne, menuFragment); // Add menu fragment at the bottom of the stack
ft.replace(R.id.fragmentOne, baseFragment);
ft.addToBackStack(null);
ft.commit();
}
rotateFromSingleToDual = true;
return;
}
rotateFromSingleToDual = true;
ft.replace(R.id.fragmentOne, menuFragment);
} else if(app().getLayoutBehavior(this) == LayoutBehavior.DUAL_FRAGMENTS) {
// We are now in dual fragments mode
if(savedInstanceState != null) {
if(rotateFromSingleToDual) {
// We just changed orientation from single fragment to dual fragments!
ft.replace(R.id.fragmentOne, menuFragment);
ft.replace(R.id.fragmentTwo, baseFragment);
ft.commit();
}
rotateFromSingleToDual = false;
return;
}
rotateFromSingleToDual = false;
ft.replace(R.id.fragmentOne, menuFragment);
ft.replace(R.id.fragmentTwo, baseFragment);
}
ft.commit();
}
This works, at least from time to time. However, many times I get java.lang.IllegalStateException: Fragment already added: MenuFragment (....)
Can anyone please give me some pointers as to how to better implement this? My current code is not pretty at all, and I'm sure many developers out there want to achieve exactly this.
Thanks in advance!
A common way to implement this scenario is to only use the fragment stack when in a mode that shows multiple fragments. When you're in the single fragment mode, you start a new activity that's sole job is to display the single fragment and take advantage of the activity back stack.
In your case you'll just need to remember the currently selected spot on rotate to set it as an argument when starting the new activity.
It's explained much better here:-
http://developer.android.com/guide/components/fragments.html
Hope that helps.
In the example on using fragments in the Android docs, when the application is in 'dualview' mode, the details fragment is recreated whenever the application needs to show details for a different title. FragmentTransaction.replace() is used to swap out each old details fragment instance with a new one.
Is this recommended practice? Isn't it wasteful to create a new UI instance when the real intent (no pun intended) is to update what the UI shows, not the UI itself. It seems to me the only reason to create new instances is if one intends to add them to the backstack so the user can retrace steps. Otherwise, is it safe/advisable to update a fragment directly?
In the case of the example, it would mean a method along the lines of DetailsFragment.setShownIndex(). This would be called, passing in the new title index, instead of recreating DetailsFragment.
Suppose we have a version of the example where one activity manages both fragments, but only shows one at a time, swapping each fragment out as needed. Would it be ok for the activity to create an instance of each fragment, retain references to each, and then simply add or remove these two instances from itself as needed?
One possibly sticky consequence of this would be that, when the titles fragment is in resumed state (i.e. in the 'foreground'), selecting a title will result in a call to DetailsFragment.setShownIndex() at a time when the details fragment is in stopped state.
Good idea? Bad idea?
Thanks in advance.
Like you said, the main reason to create new Fragment instances is for ease of using the back stack. It is also perfectly safe to reuse an existing Fragment (looking it up using either FragmentManager.findFragmentById() or FragmentManager.findFragmentByTag()). Sometimes you'll need to make good use of the Fragment methods like isVisible(), isRemoving() etc. so you don't illegally reference UI components when the DetailsFragment is stopped.
Anyway in your proposed single-pane Activity with 2 fragments, your setShownIndex method could set a private field in DetailsFragment which is loaded in onCreateView or onActivityCreated.
e.g.,
DetailsFragment df = getFragmentManager().findFragmentByTag("details");
if (df != null) {
df.setShownIndex(getSelectedIndex());
} else {
df = DetailsFragment.newInstance(getSelectedIndex());
}
fragmentTransaction.replace(R.id.frame, df, "details").commit();
In both cases, whether df is newly created or reused, onCreateView and onActivityCreated will be called when the DetailsFragment gets added to the container.
But if you want a back stack, I highly recommend just creating new instances, otherwise you're just implementing your own back stack for the contents of the DetailsFragment.
I have tried the following code and it works for me :
private void replaceFragment(Class fragmentClass, String FRAGMENT_NAME, android.support.v4.app.FragmentManager fragmentManager) {
Fragment fragment = null;
String backStateName = fragmentClass.getName(); // nome della classe del Fragment
Log.d("Fragment: ", "Creazione Fragment: "+backStateName);
Boolean fragmentExit = isFragmentInBackstack(fragmentManager, backStateName);
if (fragmentExit) { //Il Fragment รจ presente nello stacback
// Fragment exists, go back to that fragment
//// you can also use POP_BACK_STACK_INCLUSIVE flag, depending on flow
fragmentManager.popBackStackImmediate(fragmentClass.getName(), 0);
} else {
// se non esiste lo aggiungiamo
try {
fragment = (Fragment) fragmentClass.newInstance();
} catch (Exception e) {
e.printStackTrace();
}
// Inizializzo la transazione del Fragment
android.support.v4.app.FragmentTransaction ft = fragmentManager.beginTransaction();
ft.setCustomAnimations(
R.anim.fragment_slide_left_enter,
R.anim.fragment_slide_left_exit,
R.anim.fragment_slide_right_enter,
R.anim.fragment_slide_right_exit);
ft.replace(R.id.frameLayout_contentMain, fragment, FRAGMENT_NAME);
ft.addToBackStack(fragmentClass.getName());
ft.commit();
// Recupero il numero di Fragment presenti
Integer nFragment = fragmentManager.getBackStackEntryCount();
Log.d("Fragment: ", "Numero di Fragment: "+nFragment);
}
}
To determine if the Fragment is already in StackBack execute this function :
public static boolean isFragmentInBackstack(final android.support.v4.app.FragmentManager fragmentManager, final String fragmentTagName) {
for (int entry = 0; entry < fragmentManager.getBackStackEntryCount(); entry++) {
if (fragmentTagName.equals(fragmentManager.getBackStackEntryAt(entry).getName())) {
return true;
}
}
return false;
}
I Hope I could help you