Android Adapter

Android Adapter

 

Adapters are the link between a set of data and the AdapterView that displays the data.

AdapterView:

• AdapterViews are ViewGroups that display child views given to it by an adapter.
•  An example of an AdapterView is a ListView. 
• Adapters also provide the child views that display the data in the AdapterView. 
• Adapters are responsible for supplying the data and creating the views representing each item.

 

•  Adapters get the data and pass it, along with a child view, to the parent AdapterView which displays the child view and the data

• The Android Framework has a set of native adapters that are easy to use. You can also create your own custom adapters if you wish.

Two of Android’s common adapters are:

ArrayAdapter:

• An ArrayAdapter is an adapter backed by an array of objects. It links the array to the Adapter View.

• The default ArrayAdapter converts an array item into a String object putting it into a TextView. The text view is then displayed in the AdapterView (a ListView for example).

• When you create the adapter, you need to supply the layout for displaying each array string. You can define your own or use one of Android’s, such as:

android.R.layout.simple_list_item_1 

• There are alternative constructors that you can use for more complex layouts. 
• You can also display images instead of strings.

Here's a tutorial where we use a custom ArrayAdapter to display a list of images and text, Using Bitmaps efficiently.

Example coding: 

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 

 xmlns:tools="http://schemas.android.com/tools"     

android:layout_width="match_parent" 

 android:layout_height="match_parent" 

 android:paddingBottom="@dimen/activity_vertical_margin"     

android:paddingLeft="@dimen/activity_horizontal_margin"     

android:paddingRight="@dimen/activity_horizontal_margin" 

 android:paddingTop="@dimen/activity_vertical_margin" 

 tools:context=".MainActivity" >

    <ListView 

 android:id="@+id/list"         

android:layout_width="wrap_content"         

android:layout_height="wrap_content" >

    </ListView>

</RelativeLayout>

list_singal.xml

<?xml version="1.0" encoding="utf-8"?>

 <TableLayout xmlns:android="http://schemas.android.com/apk/res/android"     

android:layout_width="match_parent" 

 android:layout_height="match_parent" >
    <TableRow>
        <ImageView 

 android:id="@+id/img" 

 android:layout_width="100dp" 

 android:layout_height="100dp"/>

        <TextView 

 android:id="@+id/txt" 

 android:layout_width="wrap_content" 

 android:textSize="40dp" 

 android:layout_height="50dp" />

    </TableRow>
</TableLayout>

MainActivity:

public class MainActivity extends Activity {
    ListView list;
    String[] web = {
            "" +
                    "bird",
            "boy",
            "butterfly",
            "follower",
            "fruits",
            "karthi",
            "nature",
            "rose"    } ;
    Integer[] imageId = {
            R.drawable.bird,
            R.drawable.boy,
            R.drawable.butterfly,
            R.drawable.follower,
            R.drawable.fruits,
            R.drawable.monkey,
            R.drawable.nature,
            R.drawable.rose,


    };

    @Override    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        CustomList1 adapter = new                CustomList1(MainActivity.this, web, imageId);
        list=(ListView)findViewById(R.id.list);
        list.setAdapter(adapter);
        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                Toast.makeText(MainActivity.this, "You Clicked at " +web[+ position], Toast.LENGTH_SHORT).show();

            }
        });

    }

}

CustomList1

public class CustomList1 extends ArrayAdapter<String> {
    private final Activity context;
    private final String[] web;
    private final Integer[] imageId;
    public CustomList1(Activity context,
                      String[] web, Integer[] imageId) {
        super(context, R.layout.list_single, web);
        this.context = context;
        this.web = web;
        this.imageId = imageId;

    }
    @Override    public View getView(int position, View view, ViewGroup parent) {
        LayoutInflater inflater = context.getLayoutInflater();
        View rowView= inflater.inflate(R.layout.list_single, null, true);
        TextView txtTitle = (TextView) rowView.findViewById(R.id.txt);

        ImageView imageView = (ImageView) rowView.findViewById(R.id.img);
        txtTitle.setText(web[position]);

        imageView.setImageResource(imageId[position]);
        return rowView;
    }
}

  Output:

 

SimpleCursorAdapter: 

The SimpleCursorAdapter links the data contained in a Cursor to an Adapter View.

Cursors:

• A cursor is a set of data. You usually get a cursor when you do a database query. The result of your query is contained in the cursor.

• The SimpleCursorAdapter binds the Cursor data to an Adapter View. You define a layout that controls how each row of data is displayed.

• Each row’s view is populated using the column values of the corresponding row in the cursor.

This layout is then displayed in the Adapter View, like a ListView for example.

• The SimpleCursorAdapter gets the data out of the Cursor, puts each row of data in a layout that you define and then displays it in the Adapter View.

• When you construct the SimpleCursorAdapter, you specify which column’s data is to be retrieved from the cursor. 

• You also specify which fields in your layout are to display this data.

•  The adapter then creates a new view for each cursor entry and populates it with the corresponding cursor column values.

Other useful Adapters:

CursorAdapter

• A CursorAdapter links a Cursor’s data to a List View.

•  You must include the database’s _id column as it’s used in processing the list item’s selection.

• The SimpleCursorAdapter is a subclass of CursorAdapter.

• The SimpleCursorAdapter is easier to use while the CursorAdapter requires more work but allows more customization.

SimpleAdapter

• The SimpleAdapter links static data to views defined in a layout file. 

• You specify the data as an ArrayList of Maps. 

• Each entry in the ArrayList will display as a row in a list.

BaseAdapter

• The BaseAdapter is a common base class for an Adapter that can be used in a ListView and a Spinner.

ListAdapter

• The ListAdapter links the data and a ListView displaying the data. 

•  The List View can display any data type provided it’s wrapped in a ListAdapter.

next we see about Listview.