I've done some research but I really couldn't find the answer.
I have single activity with side menu, and holder. I have many (non support) fragments, and all of them are using same holder (one at a time).
When user uses menu (it's in main activity), and goes another page, I want to add name of the current fragment to backstack (using .addToBackStack(Fragment1.class.getName())), but I couldn't find how to get current fragment.
I don't want to implement interface etc to keep track of current fragment. There is a super simple way using fragmentManger isn't there?
You can get your current fragment like this:
if (getFragmentManager().getBackStackEntryCount() > 1) {
Fragment f = getFragmentManager().findFragmentById(R.id.content_frame);
if (f instanceof BlankFragment) {
// Do something
}
}
OK,
If you want to get latest entry from backstack(thanks to #AndroidGeek);
fragmentManager.getBackStackEntryAt(fragmentManager.getBackStackEntryCount()-1);
and, if you want to get currently active fragment (thanks to #Salman500 #AndroidGeek);
Fragment f = getFragmentManager().findFragmentById(R.id.fragment_holder);
you can use this to get fragment id for non support fragment
Fragment fragment = getFragmentManager().findFragmentById(R.id.fragment_id);
if(fragment!=null)
{
getFragmentManager()
.beginTransaction()
.addToBackStack(null)
.commit();
}
You can keep track of fragments in the main activity (with variables) and access them there. Example:
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction transaction= manager.beginTransaction();
MyFragment myFragment = new MyFragment();
myFragment.doSomething();
Adding to the back-stack:
FragmentTransaction fragment = getSupportFragmentManager().beginTransaction();
fragment.addToBackStack(fragment);
fragment.commit();
This is answered here: get currently displayed fragment
Just use addToBackStack() before you commit() the fragment trancsaction. See it here
So your code will look like :
...
fragmentTransaction.replace(R.id.holder, newFragmentToShow, newFragmentTag);
fragmentTransaction.addToBackStack();
fragmentTransaction.commit();
...
EDIT : after OP was edited
You do not need the fragment class to call addToBackStack() as you have mentioned in the OP. The String argument is an optional string just to keep the state for the backstack state. You should see the documentation
It is all internally managed and the current active fragment is automatically added to the backStack, you may call it from where ever you want, it will always use current active fragment.
Related
I have a problem with the backstack behaviour. That is what I am doing:
add(fragment1) + addToBackStack(null)
replace(fragment2) + addToBackStack(null)
What is happening:
Fragment 1 is added and in the backstack
Then the second fragment replaces the first one and it is added to the backstack.
Now I want to change my last backstacked fragment with a new transaction which put a new backstack fragment so:
[frag1, frag2] becomes [frag1, frag3]
but this transaction made by a popBackStack + replace is making the frag1 to load by calling its onCreateView and onActivityCreated. I know this is the expected behaviour since this is how backstack works, but I am trying to find a way to avoid this preload.
Edit
In this question I am using the concept of backstack fragment for the transaction to be more clear. Every transaction here is an add+remove (which is a replace).
The code for replace I am using is:
public int replaceFragment(BaseFragment newFragment, boolean addToBackStack, boolean animated, PopStackMode popMode) {
if (popMode != null) {
getSupportFragmentManager().popBackStack(newFragment.getFragmentTag(), popMode == PopStackMode.POP_INCLUSIVE ? FragmentManager
.POP_BACK_STACK_INCLUSIVE : 0);
}
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
if (animated) {
ft.setCustomAnimations(R.anim.slide_in_left, 0, R.anim.slide_out_right, 0);
}
ft.replace(R.id.fragment_container, newFragment, newFragment.getFragmentTag());
if (addToBackStack) {
ft.addToBackStack(newFragment.getFragmentTag());
}
return ft.commit();
}
You can see I am creating a navigation history based on the fragment backstack, as it was kind of a browser. When a "page" is added there is a fragment and a backstack transaction. In this context, I trying to:
Remove the current fragment.
Remove the transaction from the backstack.
Add a new fragment without poping and loading the previous backstack fragment.
I hope it is more clear.
Edit 2
I have filled a request feature for a flag that supports this behavior. Find it here.
First, you should understand that the backstack doesn't save fragments, but it saves transactions instead. When you call popBackStack what it actually does is revert the previous transaction. More on this here.
I think that you can do this:
Name your transactions by providing a unique name to your addToBackStack instead of null. i.e. addToBackStack("frag1").
Don't call popBackStack + replace, but instead just call replace.
Then, in your activity, override your onBackPressed and if the current fragment being displayed is Frag3 (you can check this using findFragmentByTag if you provided a tag in the replace method) you can call getSupportFragmentManager().popBackStackImmediate("frag1", FragmentManager.POP_BACK_STACK_INCLUSIVE); (otherwise call the super.onBackPressed)
I've setup a new Android project that comes with an activity. Here's the boiler plate code:
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
Can someone explain what this is doing exactly? From what I can see, it checks if the activity hasn't been initliazed and then inflates the layout. But what I don't understand is beginTransaction(), ew PlaceholderFragment(), and commit()
Thanks.
You use fragment transactions to add / replace (etc) fragments within a FrameLayout (R.id.container) and new PlaceholderFragment is a new instance of a fragment to be put into the container
//Check whether we're recreating a previously destroyed instance
if (savedInstanceState == null) {
//Execute a transaction, replacing any existing fragment with this one inside the frame.
//Getting FragmentManager object which will control fragment acvitiy
FragmentManager fm = getFragmentManager()
//Starting a FragmentTransaction which will handle transaction to this fragment activity
FragmentTransaction ft = fragmentManager.beginTransaction();
//Add a fragment to the activity state. This fragment may optionally also have its view (if Fragment.onCreateView returns non-null) into a container view of the activity.
ft.add(R.id.container, new PlaceholderFragment());
//Schedules a commit of this transaction.
ft.commit();
}
There is a good explanation to fragment activity here, here and here
FragmentManager is a class which helps in managing the fragments that an activity may need. So here you are basically getting an instance of it and you are beginning a transaction. You need an instance of transaction because it lets the runtime know that some change is going to happen when this is called. Here 'add()' is that change and finally you commit it to save that change.
The arguments to add are the layout where the fragment needs to be added and the PlaceHolderFragment() is the name of the Fragment you need to put in.
As fragments are the way to go, replacing all of many heavy Activites, Eclipse has also adapted to this change which cause the boiler alert. :)
Starting a fragment (which cant be done via Intents) is treated as a transaction just like in database (not a good example i guess).
getFragmentManager() - gets the Activities FragmentManger which is responsible to initiate FragmentTransaction.
beginTransaction() - creates a new Transaction for this particular fragment job.
new PlaceholderFragment() - is an instance of the PlaceholderFragment which you can find if scroll more in the Activity.
commit - a way to commit this trasaction and bring it to effect.
See Android docs. for more details. :)
It is simple my friend.
In simple Coding Language:
if (savedInstanceState == null) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.add(R.id.tab5, new PlaceholderFragment());
fragmentTransaction.commit();
}
If you think that it explain everything, then it is a pleasure for me. Otherwise just ping me to add theory information.
I'm trying to decide and show a fragment in activity's onResume method, but in case a previously added fragment is chosen again, then the activity goes blank.
Sample code (with one fragment):
#Override
protected void onResume(){
FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
trans.replace(R.id.myLayout, fragA);
trans.commit();
getSupportFragmentManager().executePendingTransactions();
}
With above code, when the activity is created for the first time, it shows fragA correctly, but in case I press Home Key and then switch back to my activity (in order to provoke onResume again), it all goes blank (seems like fragA is removed).
Is replacing a previously added fragment removes itself? or how not to loose a fragment if it is replaced by itself?
You can't replace a fragment with itself. The first half of a replace is a removal of the previous fragment at that id. Once a fragment is removed it can no longer be added or used by the fragment manager (so the add portion of the replace will not work properly).
Depending on your use case, you have two options:
Create a new fragment instead of reusing the existing instance
Use some other method to see if its necessary to replace your fragment
Finally, you probably don't need to call executePendingTransactions.
You can try:
if( !(getSupportFragmentManager().findFragmentById(R.id.myLayout) instanceof FragmentA) ) {
FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
trans.replace(R.id.myLayout, fragA);
trans.commit();
}
And I assume that fragA is FragmentA class object.
Finally, I had to put a check before replacing fragments. In case, an (already added) fragment is requested for replace again, I had to check if its already added then ignore the replacement, else proceed. For example:
#Override
protected void onResume() {
if (!fragA.isAdded()) {
FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
trans.replace(R.id.myLayout, fragA);
trans.commit();
//getSupportFragmentManager().executePendingTransactions(); //unnecessary
}
}
When referencing back to a created Fragment please do make sure to try adding the
fragmentTransaction.addToBackStack(null);
method right before committing so that your Fragment is resumed instead of destroyed as mentioned in the developer guides.
If you don't call addToBackStack() when you perform a transaction that removes a fragment, then that fragment is destroyed when the transaction is committed and the user cannot navigate back to it. Whereas, if you do call addToBackStack() when removing a fragment, then the fragment is stopped and is later resumed if the user navigates back.
You can find this at the end of this page.
I was studying Fragments and got little confused on differentiating FragmentTransaction.replace(id, fragment, tag) and FragmentTransaction.addToBackStack(tag) calls. Lets say that my current fragment is FragmentA and then I loaded FragmentB. I want that in future, when I need to load FragmentA, I don't have to reload it. Just load the old one in old state. I used the following code segment:
public void loadFragment(Fragment fragmentB, String tag) {
FragmentManager fm = getSupportFragmentManager();
View fragmentContainer = findViewById(R.id.fragment_container);
FragmentTransaction ft = fm.beginTransaction();
ft.replace(fragmentContainer.getId(), fragmentB, tag);
ft.addToBackStack(tag);
ft.commit();
}
Now I am confused, where should I add the string tag? In replace() or in addToBackStack() or in both calls? Can you explain the difference between these two tag places?
Can you explain the difference between these two tag places?
The documentation for addToBackStack is pretty clear:
An optional name for this back stack state, or null.
While for replace:
Optional tag name for the fragment, to later retrieve the fragment
with FragmentManager.findFragmentByTag(String).
So these two parameters are independent, one identifies the back stack, while the other identifies the fragment within Activity's FragmentManager.
Your code seems correct from this point of view, just that I would not search the fragmentContainer view by its id, only to use then its id for replacing the fragment. Make it simpler:
public void loadFragment(Fragment fragmentB, String tag) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.fragment_container, fragmentB, tag);
ft.addToBackStack(null);
ft.commit();
}
In case you don't need to identify this back stack later on, pass null for addToBackStack. At least I'm always doing it.
In this example you don't need to add tags as identification.
Just do:
ft.replace(R.id.fragment_container,fragmentB);
ft.addToBackStack(null);
ft.commit();
The tag as identification is commonly used when you want to add a fragment without a UI.
Passing null to addtoBackStack(null) means adding the fragment in the Fragment Stack but not adding any TAG which could be further use to identify the particular fragment in a stack before adding again.
.addToBackStack(null);
But passing TAG to addToBackStack helps in identifying the fragment in Fragment stack by TAG.
Like
.addToBackStack(FragmentName.TAG);
Now we can check the fragment before adding it to the Stack :
getFragmentManager().findFragmentByTag(SettingsFragment.TAG);
This will return null if the Fragment is not already added.
Param passed to addToBackStack() can be used to retrieve the whole BackStackEntry object, not just a single fragment. In order to set the fragment tag, consider using 3-param versions of add(int, Fragment, String) and replace(int, Fragment, String)
Prior to adding the Fragment you will be able to check if this Fragment is already in the backstack using :
getFragmentMangager().findFragmentByTag(SettingsFragment.TAG);
This will return null if the Fragment is not already added.
When I press a button, my app creates a fragment. I'd like to make sure that only one of this fragment is created, e.g. disable the button if the fragment already exists.
How do I check that it creates only one fragment? Is it possible to get a Fragment count or is there some option that limits it to creating only one?
You can use the methods that sandrstar mentioned. When attaching a fragment u can first check to see if its already attached.
For example if you are adding the fragment dynamically you can stop the fragment from being re-added by doing the following:
MyFragment myFragment = getFragmentManager().findFragmentByTag("MyFragmentTag")
if(myFragment == null)
{
myFragment = MyFragment.newInstance();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(R.layout.mylayout,myFragment,"MyFragmentTag");
ft.commit();
}