Develop Reference

is fine to open a new fragment in fragment?

I want to separate logic fragment from activity but the problem is I make api call and save data in fragment. And when user click a item in fragment. I need to send parcelable data to other fragment to show detail info about item.
Is launching fragment in fragment anti pattern for android ?
I would like to hear some opinion about this matter.

Yes, is totally an anti-pattern, remember that you need to see the Activity as a container and fragments as independent sub-screens, so is the Activity responsibility to manage the fragments. I.e.: If you have a Post activity you can have a PostText fragment, a PostImage fragment and all of that is manage by the activity, every fragment is attached to an Activity.

It is not a common practice to have a nested fragment inside a fragment even it can be done. However, it would be better to have an activity as the centric container for all your fragments. You can use EventBus (GreenRobot / Otto) to separate the concerns and do all the API calls in another class and send the results by subscribing to this event.

Update Activity title from fragment in FragmentPagerAdapter

I have v4.ViewPager inside Activity and use SlidingTabLayout from google's examples SlidingTabBasics. The problem I encounter is that each fragment retrieved from getItem(position) in v4.FragmentPagerAdapter has to refresh activity title. I have already learnt the hard way that FragmentPagerAdapter causes fragments to have really weird life callbacks so I can't probably use onResume or onStart. I noticed though that onCreateOptionsMenu(menu,inflater) gets called exactly when I want to refresh activity title. Is there a callback to supply actions when ViewPager has settled the fragment and it should change activity title?
Setting callback on ViewPager.onPageSelected(position) is inconvenient because I want this information to be propagated from fragment, not to fragment.
Currently I 'steal' onCreateOptionsMenu(menu,inflater) to do the work for me but it causes optimisation issues when no menu should be inflated but I still want the fragment to be able to affect activity title.

Have you tried this code in your fragment:
if(getActivity() != null){
getActivity().setTitle("new title");
}
Take into consideration that getActivity() will be null if the fragment is not yet attached to the activity.
Godspeed.

You can do this in different ways.
You can use interfaces in fragments that can be implemented by activity. But the drawback is, if you do have large number of fragments you must implement all of them.

Where to put the Fragment functional code?

Just a general question about working with Fragments and Activitys for android development: where does the business end of the functional code go for Fragments loaded into an Activity dynamically? (i.e. a fragment's OnClickListeners, OnCheckedChangedListeners, button logic methods...)
Do they go in the Fragment class, or the Activity class?

All the GUI logic for views attached to a fragment should be contained inside the fragment itself.
Thus a fragment should be as self contained as possible.
You can, though, if necessary do callbacks to your activity based on fragment GUI interaction. This can easily be done like this inside the fragment:
#Override
public void onAttach(Activity activity) {
if (!(activity instanceof SherlockFragmentActivity)) {
throw new IllegalStateException(getClass().getSimpleName()
+ " must be attached to a SherlockFragmentActivity.");
}
mActivity = (SherlockFragmentActivity) activity;
super.onAttach(activity);
}
In this specific case the reason for gaining a reference to SherlockFragmentActivity is to gain access to the support menu inflater mActivity.getSupportMenuInflater(), hence the construction can of course also serve to gain information from the underlying activity.

This probably depends on how much the Fragment's functionalities have in common, and how many, let's say Buttons, have to be handled.
I personally (and it's probably most common practice) handle onClick(...) events separately for each Fragment, meaning that I let each Fragment implement it's own OnClickListener.
Furthermore, when handling everything through the Activity, probably not all the components that react to click-events are in memory at all times and can be reached via findViewById(...), depending on which Fragment is currently displayed and how your user-interface is built up in general.

they always in fragment class because fragment is one type of component in android which we can reuse it. if we put onclick and oncheckchanged in activity then what meaning of reusing that component??
for more information about please go through following step:
Link 1 for basic level of information about fragment and how to handle them
Link 2 for dealing with multi pane fragment
Standard site for fragment

It depends:
If fragment can handle logic which is self sufficient(complete) then that code can be handled by fragment. e.g. on click call phone number.
If fragment have UI whose action is activity specific, then you want to add listener in activity.
e.g. master detail view like email client, on tablet user click on title fragment1 which have list of email titles, then handler on click in activity can show detail fragment2 in activity.
In all you want to keep fragment reusable.

Communication fragments/activities

In my existing app I am porting two activities to fragments. The case is the classic dual panel mode with a list on the left and the content on the right.
The doc says that I should avoid to manipulate fragments within fragments, passing instead through the host activity. Said that I am using callbacks to the activity.
The first doubt (maybe banal) I have is:
How to avoid to duplicate the same code in the activity that hosts the
2 fragments and into the activity that wraps the fragment when not in
dual mode?
I'll try to explain. So I have:
ListFragment and ListFragmentActivity
ContentFragment and ContentFragmentActivity
because both fragments can live independently from each other, then:
HostActivity
that implements a listener invoked from ListFragment for adding/replacing the ContentFragment
My question is: when ListFragment is instead hosted from ListFragmentActivity, how to avoid to duplicate the code present in the HostActivity into ListFragmentActivity.
Guess I am missing something, thanks in advance.

Get rid of ListFragmentActivity. Have HostActivity handle the case where there is either one or both fragments. Then, by definition, there is no code duplication. See: https://github.com/commonsguy/cw-omnibus/tree/master/LargeScreen/EU4You

How to load new fragment in same space as current fragment

I'm looking for some advice on the best way to handle fragments which launch other fragments.
I'm converting an app which I started writing using a more Activity based approach and have since begun moving it over to using Fragments. I have some Fragments which used to launch a new Activity and I want to move them over to launching other Fragments in the same view that the current Fragment is residing.
For example - I have an Activity which has a WebView which uses a WebViewClient to handle internal js->java interactions. My WebViewClient can launch other Activities, which I used to do with :
i = new Intent(context, GoogleMapActivity.class);
startActivity(i);
This webview activity can either be fullscreen or in a view with a menu on the side, but I want the webview to respect the layout - so if the menu is present, it should stay present when launching new Fragments - I just don't know the best approach to writing the code which launches the Fragments.
So...is there a way, within a Fragment, of essentially telling a new Fragment to load in to the same space as the current Fragment or does there need to be some interaction with the Activity?
** EDIT **
Given that there are a few different layouts which could be used, I don't always know which id I should be targeting to put the fragment in - hence I need to know if there's a way to do this without knowing the id (as in the replace method for example).

getFragmentManager().beginTransaction()
.replace(((ViewGroup) getView().getParent()).getId(), fragment)
.addToBackStack(null)
.commit();
This should replace parent container with desired fragment.

That should be doable via FragementManager.replace(). Have a look at the documentation for Fragment and especially the longer example in the "Layout" section there.

If you want to add Fragment rather replace it, use:
getFragmentManager().beginTransaction().add(R.id.fragment_container, new Fragment()).commit();