CONTENT PROVIDER

Content providers store and retrieve data and make it accessible to all applications. They're the only way to share data across applications; there's no common storage area that all Android packages can access. Android ships with a number of content providers for common data types (audio, video, images, personal contact information, and so on). You can see some of them listed in the android.provider package. You can query these providers for the data they contain (although, for some, you must acquire the proper permission to read the data).

If you want to make your own data public, you have two options: You can create your own content provider (a ContentProvider subclass) or you can add the data to an existing provider if there's one that controls the same type of data and you have permission to write to it.

9.1 CONTENT PROVIDER BASICS

How a content provider actually stores its data under the covers is up to its designer. But all content providers implement a common interface for querying the provider and returning results — as well as for adding, altering, and deleting data.

It's an interface that clients use indirectly, most generally through ContentResolver objects. You get a ContentResolver by calling getContentResolver() from within the implementation of an Activity or other application component:

ContentResolver cr = getContentResolver();

Content providers expose their data as a simple table on a database model, where each row is a record and each column is data of a particular type and meaning. For example, information about people and their phone numbers might be exposed as follows:

ID	NUMBER	NUMBER_KEY	LABEL	NAME	TYPE
13	(425) 555 6677	425 555 6677	Kirkland office	Bully Pulpit	TYPE_WORK
44	(212) 555-1234	212 555 1234	NY apartment	Alan Vain	TYPE_HOME
45	(212) 555-6657	212 555 6657	Downtown office	Alan Vain	TYPE_MOBILE
53	201.555.4433	201 555 4433	Love Nest	Rex Cars	TYPE_HOME

Every record includes a numeric _ID field that uniquely identifies the record within the table. IDs can be used to match records in related tables — for example, to find a person's phone number in one table and pictures of that person in another.

A query returns a Cursor object that can move from record to record and column to column to read the contents of each field. It has specialized methods for reading each type of data. So, to read a field, you must know what type of data the field contains.

9.2 URIs

If you're defining a content provider, it's a good idea to also define a constant for its URI, to simplify client code and make future updates cleaner. Android defines CONTENT_URI constants for all the providers that come with the platform. For example, the URI for the table that matches phone numbers to people and the URI for the table that holds pictures of people (both controlled by the Contacts content provider) are:

android.provider.Contacts.Phones.CONTENT_URI
android.provider.Contacts.Photos.CONTENT_URI

The URI constant is used in all interactions with the content provider. Every ContentResolver method takes the URI as its first argument. It's what identifies which provider the ContentResolver should talk to and which table of the provider is being targeted.

Using a Content Provider
Here are some of Android's most useful built-in content providers

Content Provider	Intended Data.
Contacts	Contact details.
Browser	Browser bookmarks, browser history, etc.
Call Log	Missed calls, call details, etc.
Media Store	Media files such as audio, video and images.
Settings	Device settings and preferences.

An example to display, display name from contacts

package a.b.c;

import java.util.ArrayList;

import android.app.ListActivity;

import android.content.ContentResolver;

import android.database.Cursor;

import android.os.Bundle;

import android.provider.ContactsContract;

import android.provider.ContactsContract.PhoneLookup;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.ArrayAdapter;

import android.widget.Button;

public class TrialcontentActivity extends ListActivity {

Button b1,b2;

ArrayList<String> results = new ArrayList<String>();

ArrayAdapter<String> arraydpter;

@Override

protected void onCreate(Bundle savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

arraydpter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,results);

b1 = (Button)findViewById(R.id.bttn1);

b1.setOnClickListener(new OnClickListener() {

public void onClick(View arg0) {

// TODO Auto-generated method stub

ContentResolver cr= getContentResolver();

System.out.println("1");

Cursor people = cr.query(ContactsContract.Contacts.CONTENT_URI, null, null, null, null);

while(people.moveToNext())

{

System.out.println("2");

int nameFieldColumnIndex = people.getColumnIndex(PhoneLookup.DISPLAY_NAME);

String contact = people.getString(nameFieldColumnIndex);

results.add(contact);

}

people.close();

setListAdapter(arraydpter);

arraydpter.notifyDataSetChanged();

}

});

b2 = (Button)findViewById(R.id.bttn2);

b2.setOnClickListener(new OnClickListener() {

public void onClick(View arg0) {

// TODO Auto-generated method stub

results.remove(0);

arraydpter.notifyDataSetChanged();

}

});

}

main.xml

<?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="fill_parent"

android:orientation="vertical" >

<TextView

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/hello" />

<Button

android:id="@+id/bttn1"

android:text="Click to get contacts"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

<Button

android:id="@+id/bttn2"

android:text="Click to delete"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

<ListView

android:id="@android:id/list"

android:layout_width="wrap_content"

android:layout_height="wrap_content"></ListView>

</LinearLayout>

Manifest file

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

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

package="a.b.c"

android:versionCode="1"

android:versionName="1.0" >

<uses-sdk android:minSdkVersion="10" />

<application

android:icon="@drawable/ic_launcher"

android:label="@string/app_name" >

<activity

android:label="@string/app_name"

android:name=".TrialcontentActivity" >

<intent-filter >

</intent-filter>

</activity>

</application>

<uses-permission android:name="android.permission.READ_CONTACTS"/>

</manifest>

Note that in this case we need to add permission to access contacts from phone.

Android

Monday, May 21, 2012