Android Topics: Fradments, contentObserver etc...,

Fragments

•       A fragment represents a behavior or a portion of user interface in aactivity.we can combine multiple fragments in a activity to build a multi pane UI.

•       While the activity is running we can manipulate each fragment separately.

Types of fragments:

•       DialogFragment :Displays a floating dialog. Using this class to create a dialog is a good alternative to using the dialog helper methods in the Activity class, because you can incorporate a fragment dialog into the back stack of fragments managed by the activity, allowing the user to return to a dismissed fragment.

•       ListFragment : Displays a list of items that are managed by an adapter (such as a SimpleCursorAdapter), similar to ListActivity. It provides several methods for managing a list view, such as the onListItemClick() callback to handle click events.

•       PrefernceFragment :Displays a hierarchy of Preference objects as a list, similar to PreferenceActivity. This is useful when creating a "settings" activity for your application.

Adding fragment:

•       A fragment is usually used as part of an activity's user interface and contributes its own layout to the activity.

•       To provide a layout for a fragment, you must implement the onCreateView() callback method, which the Android system calls when it's time for the fragment to draw its layout. Your implementation of this method must return a View that is the root of your fragment's layout.

•       Note: If your fragment is a subclass of ListFragment, the default implementation returns a ListView from onCreateView(), so you don't need to implement it.

Example:

public static class ExampleFragment extends Fragment {

 @Override

public View onCreateView(LayoutInflaterinflater, ViewGroup container, Bundle savedInstanceState) {

// Inflate the layout for this fragment return

inflater.inflate(R.layout.example_fragment, container, false);

  }

 }

•       The inflate() method takes three arguments:

•       The resource ID of the layout you want to inflate.

•       The ViewGroup to be the parent of the inflated layout. Passing the container is important in order for the system to apply layout parameters to the root view of the inflated layout, specified by the parent view in which it's going.

•       A boolean indicating whether the inflated layout should be attached to the ViewGroup (the second parameter) during inflation. (In this case, this is false because the system is already inserting the inflated layout into the container—passing true would create a redundant view group in the final layout.)

Adding fragment in Manifest:

<LinearLayoutxmlns: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>

Adding fragment programmatically:

FragmentManagerfragmentManager = getFragmentManager()FragmentTransactionfragmentTransaction =  fragmentManager.beginTransaction();

ExampleFragment fragment = new ExampleFragment(); fragmentTransaction.add(R.id.fragment_container, fragment); fragmentTransaction.commit();

// Create new fragment and transaction Fragment newFragment = new ExampleFragment();

FragmentTransaction transaction = getFragmentManager().beginTransaction();

// Replace whatever is in the fragment_container view with this fragment,

// and add the transaction to the back stack transaction.replace(R.id.fragment_container, newFragment); transaction.addToBackStack(null); // Commit the transaction transaction.commit();

Adaptor

•       An Adapter object acts as a bridge between an AdapterView and the underlying data for that view. The Adapter provides access to the data items. The Adapter is also responsible for making a View for each item in the data set.

•       registerDataSetObserver(DataSetObserver observer) Register an observer that is called when changes happen to the data used by this adapter.

•       unregisterDataSetObserver(DataSetObserver observer),Unregister an observer that has previously been registered with this adapter via registerDataSetObserver(DataSetObserver).

•       getCount() How many items are in the data set represented by this Adapter.

•       getItem(int position) Get the data item associated with the specified position in the data set

ArraryAdapter

•       A concrete BaseAdapter that is backed by an array of arbitrary objects.

•       By default this class expects that the provided resource id references a single TextView.

•       TextView is referenced, it will be filled with the toString() of each object in the array. we can add lists or arrays of custom objects. Override the toString() method of our objects to determine what text will be displayed for the item in the list.

Example:

public class ArrayAdapterDemo extends ListActivity {
   TextView selection;
   String[] items = { "this", "is", "a", "really",
   "silly", "list" };
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
setListAdapter(new ArrayAdapter<String>(
      this,
      android.R.layout.simple_expandable_list_item_1,
      items));
selection=(TextView)findViewById(R.id.selection);
   }

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
super.onListItemClick(l, v, position, id);
String text = " position:" + position + "  " + items[position];
selection.setText(text);
}
     
}

Cursor Adapter

•       Adapter that exposes data from a Cursor to a ListView widget. The Cursor must include a column named "_id" or this class will not work.

•       public class MessageAdapter extends CursorAdapter {
   private Cursor mCursor;
   private Context mContext;
   private final LayoutInflatermInflater;


    public MessageAdapter(Context context, Cursor c) {
        super(context, c);
        mInflater=LayoutInflater.from(context);
    mContext=context;
    }

    @Override
    public void bindView(View view, Context context, Cursor cursor) {

        TextViewmobileNo=(TextView)view.findViewById(R.id.mobileNolistitem);
        mobileNo.setText(cursor.getString(cursor.getColumnIndex(TextMeDBAdapter.KEY_MOBILENO)));

        TextView frequency=(TextView)view.findViewById(R.id.frequencylistitem);
        frequency.setText(cursor.getString(cursor.getColumnIndex(TextMeDBAdapter.KEY_FREQUENCY)));

        TextViewrowid=(TextView)view.findViewById(R.id.rowidlistitem);
        rowid.setText(cursor.getString(cursor.getColumnIndex(TextMeDBAdapter.KEY_ID)));

    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        final View view=mInflater.inflate(R.layout.message_list_item,parent,false);
        return view;
    }

} 

SimpleCursorAdapter

•       An easy adapter to map columns from a cursor to TextViews or ImageViews defined in an XML file. we can specify which columns we want, which views we want to display the columns, and the XML file that defines the appearance of these views.

Exampe:

•       public class ContentUserDemo extends Activity {

•       private static final String TAG = "ContentUserDemo";

•        

•           /** Called when the activity is first created. */

•           @Override

•       public void onCreate(Bundle savedInstanceState) {

•       super.onCreate(savedInstanceState);

•       setContentView(R.layout.main);

•        

•             // Get content provider and cursor

•       ContentResolvercr = getContentResolver();

•             Cursor cursor = cr.query(Settings.System.CONTENT_URI, null, null, null, null);

•        

•             // Let activity manage the cursor

•       startManagingCursor(cursor);

•       Log.d(TAG, "cursor.getCount()=" + cursor.getCount());

•        

•             // Get the list view

•       ListViewlistView = (ListView) findViewById(R.id.listView);

•             String[] from = { Settings.System.NAME, Settings.System.VALUE };

•       int[] to = { R.id.textName, R.id.textValue };

•       SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.row, cursor, from, to);

•       listView.setAdapter(adapter);

•           }

•       }

ContentObserver

•       Receives call backs for changes to content. Must be implemented by objects which are added to a ContentObservable.

Example

private class MyContentObserver extends ContentObserver {

        public MyContentObserver() {
            super(null);
        }

        @Override
        public void onChange(booleanselfChange) {
            super.onChange(selfChange);
            System.out.println (" Calling onChange" );
        }

    }

MyContentObservercontentObserver = new MyContentObserver();
context.getContentResolver().registerContentObserver (People.CONTENT_URI, true, contentObserver);