A Fragment
is a section of an Activity
, which has:
- its own lifecycle
- receives its own input events
- can be added or removed while the
Activity
is running.
A Fragment
must always be embedded in an Activity
.
Fragments
are not part of the API prior to HoneyComb (3.0). If you want to use Fragments
in an app targeting a platform version prior to HoneyComb, you need to add the Support Package to your project and use the FragmentActivity
to hold your Fragments
. The FragmentActivity
class has an API for dealing with Fragments
, whereas the Activity
class, prior to HoneyComb, doesn’t.
If your project is targeting HoneyComb or newer only, you should use Activity
and not FragmentActivity
to hold your Fragments
.
Some details:
Use android.app.Fragment
with Activity
. Use android.support.v4.app.Fragment
with FragmentActivity
. Don’t add the support package Fragment
to an Activity
as it will cause an Exception to be thrown.
A thing to be careful with: FragmentManager
and LoaderManager
have separate support versions for FragmentActivity:
If you are using a Fragment
in an Activity
(HoneyComb and up), call
getFragmentManager()
to getandroid.app.FragmentManager
getLoaderManager()
to getandroid.app.LoaderManager
if you are using a Fragment
in a FragmentActivity
(pre-HoneyComb), call:
getSupportFragmentManager()
to getandroid.support.v4.app.FragmentManager
.getSupportLoaderManager()
to getandroid.support.v4.app.LoaderManager
so, don’t do
//don't do this
myFragmentActivity.getLoaderManager();
//instead do this:
myFragmentActivity.getSupportLoaderManager();
or
//don't do this:
android.app.FragmentManager fm = myFragmentActivity.getSupportFragmentManager();
//instead do this:
android.support.v4.app.FragmentManager fm = myFragmentActivity.getSupportFragmentManager()
Also useful to know is that while a fragment has to be embedded in an Activity
it doesn’t have to be part of the Activity
layout. It can be used as an invisible worker for the activity, with no UI of its own.