Andriod Fragments

A Fragment represents a behavior or a portion of user interface in an Activity. You can combine multiple fragments in a single activity to build a multi-pane UI and reuse a fragment in multiple activities. You can think of a fragment as a modular section of an activity, which has its own lifecycle, receives its own input events, and which you can add or remove while the activity is running (sort of like a "sub activity" that you can reuse in different activities).


You should design each fragment as a modular and reusable activity component.

public static class ExampleFragment extends Fragment {    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,                             Bundle savedInstanceState) {        // Inflate the layout for this fragment        return inflater.inflate(R.layout.example_fragment, container, false);    }}


For example, here's the layout file for an activity with two fragments:
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="horizontal"    android:layout_width="match_parent"    android:layout_height="match_parent">    <fragment android:name="com.example.news.ArticleListFragment"            android:id="@+id/list"            android:layout_weight="1"            android:layout_width="0dp"            android:layout_height="match_parent" />    <fragment android:name="com.example.news.ArticleReaderFragment"            android:id="@+id/viewer"            android:layout_weight="2"            android:layout_width="0dp"            android:layout_height="match_parent" /></LinearLayout>


programmatically add the fragment to an existing ViewGroup.
At any time while your activity is running, you can add fragments to your activity layout. You simply need to specify a ViewGroup in which to place the fragment.

To make fragment transactions in your activity (such as add, remove, or replace a fragment), you must use APIs from FragmentTransaction. You can get an instance of FragmentTransaction from your Activity like this:

FragmentManager fragmentManager = getFragmentManager()FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();You can then add a fragment using the add() method, specifying the fragment to add and the view in which to insert it. For example:

ExampleFragment fragment = new ExampleFragment();fragmentTransaction.add(R.id.fragment_container, fragment);fragmentTransaction.commit();The first argument passed to add() is the ViewGroup in which the fragment should be placed, specified by resource ID, and the second parameter is the fragment to add.

Once you've made your changes with FragmentTransaction, you must call commit() for the changes to take effect.


Communicating with the Activity:
Although a Fragment is implemented as an object that's independent from an Activity and can be used inside multiple activities, a given instance of a fragment is directly tied to the activity that contains it.

Specifically, the fragment can access the Activity instance with getActivity() and easily perform tasks such as find a view in the activity layout:

View listView = getActivity().findViewById(R.id.list);Likewise, your activity can call methods in the fragment by acquiring a reference to the Fragment from FragmentManager, using findFragmentById() or findFragmentByTag(). For example:

ExampleFragment fragment = (ExampleFragment) getFragmentManager().findFragmentById(R.id.example_fragment);