Download Android Content Providers

Android Content Providers &
SQLite
COMP467 MOBILE MODULE
Why Content Providers
 The underlying Linux kernel treats each Android App as
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a separate user/process.
Apps are “sandboxed” such that by default direct data
sharing is not allowed.
Content Providers are a way to share data across apps.
Content Providers centralize data into one place and
have other apps access it.
Together, providers and provider clients offer a
consistent, standard interface to data that also handles
inter-process communication and secure data access.
Content Providers Intro
 Functions much like a database providing query(),
insert(), delete() and update() methods.
 In most cases, data is stored in a SQlite databases or
flat files
Example Content Providers
 Contacts
 MediaStore
 Bookmarks
 User dictionary
 Settings
Content Provider APIs
Client
Provider
Content
Provider
Application
Data
Content Provider Intro
 You must extend the ContentProvider class to create
your content provider.
 E.g.
public class KbContentProvider extends ContentProvider {
//
}
Content URI
 Used to specify a particular content provider
 Four Parts:
 Scheme: For providers is always content://
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Authority: Has to be unique for each content provider. The
convention is to use Java Package rules (reversed domain
name of org + qualifier for each provider.
content://authority/optionalPath/optionalId
Content URI
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Path:This indicates the type of data that this particular
provider provides. For example, if you are getting all the
contacts from the Contacts content provider, then the data
path would be people and URI would look like
this content://contacts/people
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ID: This specifies the specific record requested. For example, if
you are looking for contact number 5 in the Contacts content
provider then URI would look like
thiscontent://contacts/people/5.
Content Provider Methods
 onCreate() This method is called when the
provider is started.
 query() This method receives a request from a
client. The result is returned as a Cursor object.
 insert()This method inserts a new record into the
content provider.
Content Provider Methods Cont.
 delete() This method deletes an existing record
from the content provider.
 update() This method updates an existing record
from the content provider.
 getType() This method returns the MIME type of
the data at the given URI.
Content Types
 First defined in RFC 1049 and refined in RFC 2045.
 Consists of a type and a subtype. Eg. image/png
Using Existing Content Providers
 Use Content Resolver to interact with Content
Provider.
 Content Resolver uses authority part of URI to
determine which provider to use.
 Obtain the ContentResolver object by calling the
getContentResolver() method on the Context object.
Content Resolver
A client application accesses the data from a content provider with
a ContentResolver object.
• The ContentResolver object provides query(), insert(), update(), and
delete() methods for accessing data from a content provider.
• The ContentResolver object invokes identically-named methods on an
instance of a concrete subclass of ContentProvider, which typically
resides in a separate application process.
• The ContentProvider acts as an abstraction layer between its data
store and the external presentation of data.
• The ContentResolver object and the ContentProvider object
automatically handle the details of inter-process communication.
https://newcircle.com/s/post/1375/android_content_provider_tutorial
Content Resolver Methods
 Gives access to Content Provider so it must
implement CRUD.
Method Usage
delete
Deletes the object(s) for the URI provided. The
URI can be item- or directory-based
insert
Inserts one object. The URI must be directorybased
query
Queries for all objects that fit the URI. The URI
can be item- or directory-based
update
Updates one or all object(s). The URI can be
item- or directory-based
Example Content Resolver
 Query operation on UserDictionary
 Here are the parameters to the method
Type
Name
Usage
URI
uri
The URI of the object(s) to access. This is the only argument that must not be null
String[]
projection
This String array indicates which columns/attributes of the objects you want to access
String
selection
With this argument you can determine which records to return
String[]
selectionArgs
The binding parameters to the previous selection argument
String
sortOrder
If the result should be ordered you must use this argument to determine the sort order
 Returns a Cursor object that can be used to traverse
the returned records.
Query Code Snippett
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15}
ContentResolver resolver = getContentResolver();
String[] projection = new String[]{BaseColumns._ID,
UserDictionary.Words.WORD};
Cursor cursor =
resolver.query(UserDictionary.Words.CONTENT_URI,
projection,
null,
null,
null);
if (cursor.moveToFirst()) {
do {
long id = cursor.getLong(0);
String word = cursor.getString(1);
// do something meaningful
} while (cursor.moveToNext());
Insert Snippet
Type
URI
Name
Usage
uri
The directory-based URI to which
to add the object. This argument
must not be null
ContentValues values
The values for the object to add.
This argument also must not be
null
1 ContentValues values = new ContentValues();
2 values.put(Words.WORD, "Beeblebrox");
3 resolver.insert(UserDictionary.Words.CONTENT_URI, values);
Delete Code Snippet
Type
Name
Usage
URI
uri
The URI of the object(s) to access. This
is the only argument which must not be
null
String
selection
With this argument you can determine
which records to delete
String[] selectionArgs
The binding parameters to the previous
selection argument
1 long noDeleted = resolver.delete
2
(Words.CONTENT_URI,
3
Words.WORD + " = ? ",
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new String[]{"Zaphod"});
Update
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values.clear();
values.put(Words.WORD, "Zaphod");
Uri uri = ContentUris.withAppendedId(Words.CONTENT_URI, id);
long noUpdated = resolver.update(uri, values, null, null);
Type
Name
Usage
URI
uri
The URI of the object(s) to access.
This argument must not be null
ContentValues
values
The values to substitute the current
data with. This argument also must
not be null
String
selection
With this argument you can
determine which records to update
String[]
selectionArgs
The binding parameters to the
previous selection argument
Contract Classes
 A contract class defines constants that
help applications work with the content
URIs, column names, and other
features of a content provider.
 Contract classes are not included
automatically with a provider
 The provider’s developer has to define
them and then make them available to
other developers.
Contract Classes Cont.
 Many of the providers included with the Android
platform have corresponding contract classes in the
package android.provider.
 For example, the User Dictionary Provider has a
contract class UserDictionary containing content
URI and column name constants.
 The content URI for the "words" table is defined in
the
constant UserDictionary.Words.CONTENT_URI.
The UserDictionary.Words class also contains
column name constants.
SQliteOpenHelper
 Used to create and update a Sqlite database within
an Android App.
 onCreate() – called when the database is accessed
and has not been created.
 onUpdate() – Called when the version number has
increased in your app code.
 Both methods are passed a SQLiteDatabase object as
a parameter.
Sqlite Example
 Let’s look at this tutorial that creates and uses a
Sqlite database within an app.
 This does not require the content provider
framework
 http://www.androidhive.info/2011/11/androidsqlite-database-tutorial/
 http://www.techotopia.com/index.php/An_Android
_SQLite_Database_Tutorial
References
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https://thenewcircle.com/s/post/1375/android_content_provider_tutorial
http://www.tutorialspoint.com/android/android_content_providers.htm
http://www.vogella.com/tutorials/AndroidSQLite/article.html
http://developer.android.com/guide/topics/providers/content-provider-creating.html
http://www.grokkingandroid.com/android-tutorial-content-provider-basics/