Lecture Mobile Application Development (119310)

Android Framework Basics

Agenda

• Framework Components Part III - Lists
  • ListActivity
  • ListView
  • Adapter
• Framework Components Part IV - Content Provider
  • Querying a ContentProvider
  • Example MediaStore

Adapter Implementation Examples

• ArrayAdapter
  • Holds an Array of arbitrary objects
  • Each object is displayed in a single TextView
  • TextView will be filled with the „toString()“ of every object
• SimpleAdapter
  • Maps data from an array to a layout defined in an XML file, e.g. a CheckBox, TextView or ImageView
• SimpleCursorAdapter
  • Maps the data results from an database query to the list items in the ListView

ArrayAdapter

• Example code using an ArrayAdapter in a ListActivity

final List<String> bandlist = asList("Deichkind", "Metallica","Queen","U2");
		
ArrayAdapter<String> bandArray = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1,bandlist);

setListAdapter(bandArray);

SimpleAdapter

• Example Layout for SimpleAdapter grid

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >
   <TextView
        android:id="@+id/item1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
   <TextView
        android:id="@+id/item2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
   <TextView
        android:id="@+id/item3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

Simple Adapter

• Example code for initializing a SimpleAdapter

      ListView lv = (ListView) findViewById(R.id.listview);
      // create content items
      String[] from = new String[]{"rowid","col_1","col_2"};
      int[] to = new int[]{R.id.item1, R.id.item2, R.id.item3};
  
      // prepare the list of all records
      List<HashMap<String, String>> fillMaps = 
  					new ArrayList<HashMap<String, String>>();
  
      for(int i = 0; i<10;i++){
          HashMap<String, String> map = new HashMap<String, String>();
          map.put("rowid", ""+i);
          map.put("col_1", "col_1_item_"+i);
          map.put("col_2", "col_2_item_"+i);
          fillMaps.add(map);
      }
      // fill in the layout
      SimpleAdapter adapter = new SimpleAdapter(this,fillMaps,
      			R.layout.simple_adapter_layout, from, to);
      lv.setAdapter(adapter);
  

Framework Components Part IV

Content Provider

Content Provider

• Standardized interface for sharing
data between and within applications
• Models content in a relational DB
  • Users of Content Providers can perform queries equivalent to SELECT, UPDATE, INSERT, DELETE
  • Data can be stored in SQLite Database or in a file
• URI addressing scheme
  • content://<authority>/<table>/[<id>]
  • Example: content://contacts/people/10

MediaStore

• Standard Android Content Provider to work with media on your device
• URI: content://media/external/audio/media
• Example data structure:

Content Resolver

• The ContentResolver can be used to query the ContentProvider, e.g.

ContentResolver resolver = getContentResolver();
Cursor cursor = resolver.query(
		        MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, //URI to CP
		        projection, //Array defining the data to select
		        selection, //String defining the criteria of the data selection
		        selectArgs, //parametes for the data selection
		        sortOrder); //specifies the result order

Content Resolver Parameters

• URI: Identifies the content using the content schema, e.g. MediaStore.Audio.Media.EXTERNAL_CONTENT_URI
• Projection
  • Define all data (table cols) that are of interest in a String[] String[] projection = { MediaStore.Audio.Media._ID, MediaStore.Audio.Media.ARTIST, MediaStore.Audio.Media.TITLE, MediaStore.Audio.Media.DATA, MediaStore.Audio.Media.DISPLAY_NAME, MediaStore.Audio.Media.DURATION };

Content Resolver Parameters

• Selection
  • Define the selection criteria like an SQL WHERE clause
  • The ? are replaced by the arguments given in the selectionArgs parameter
    • Works similar to the prepared statements in SQL queries and should be used in order to prevent SQL injection
    • Can be null if no selection conditions should be applied
  • Example selecting by artist name:

String selection = MediaStore.Audio.Media.ARTIST + " LIKE ?";

Content Resolver Parameters

• SelectionArgs
  • Replace the ? in the Selection String
  • null if no arguments exist

String[] selectionArgs = new String[]{"blur"};

Content Resolver Parameters

• SelectionArgs
  • Replace the ? in the Selection String
  • null if no arguments exist

String[] selectionArgs = new String[]{"blur"};

• SortOrder
  • Defines the order of the data returned in the Cursor or null if no order should be applied
  • Example ordering by the duration of the title

String sortOrder = MediaStore.Audio.Media.DURATION;

Content Resolver

• Overview of parameters of the query() method

Cursor

• The result of the ContentProvider query is stored in a Cursor object providing random read-write access to the result set
• Example iterating over a cursor´s result set

final List<String> songs = new ArrayList<String>();

while(cursor.moveToNext()){		                                                 		     

	songs.add(cursor.getString(1));

}

SimpleCursorAdapter

• Example code using a SimpleCursorAdapter to fill a ListView:

ContentResolver resolver = getContentResolver();
Cursor cursor = resolver.query(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,
	new String[]{MediaStore.Audio.Media._ID,MediaStore.Audio.Media.ARTIST,
    			MediaStore.Audio.Media.ALBUM}, null, null, null);
//define which content should be placed where in the layout
String[] from = new String[]{MediaStore.Audio.Media.ARTIST,MediaStore.Audio.Media.ALBUM};
int[] to = new int[]{R.id.artist,R.id.album};

SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.artist_list,
		cursor, from, to, SimpleCursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);
//artistList is the ListView object
artistList.setAdapter(adapter);

Android Assignment

• Conduct the Android assignment 04 on ListViews
  • Create an app with a ListView and use an Adapter to fill the list with data loaded from a ContentProvider (in this case the MediaStore)

Summary

• A ListView uses the delegate pattern
  • The Adapter is the delegate the defines the content and how the list is presented
    • This is the same pattern used on iOS for TableViews
• ContentProvider is the standard interface to access device specific data on Android such as
  • Contacts, Calendar or Media
• ContentResolver allows to query data from a ContentProvider
  • The result set is accessible using the Cursor

Recab Questions

• Which Software Architecture Pattern is used with the ListAdapter?
• How do you retrieve Data from a ContentProvider?
• What is the “?” used for in the selection string?
• What is a Cursor?
• How do you define the list’s cell content?