1. Android Content Providers & SQLite
COMP467 Mobile Module

2. Why Content Providers
The underlying Linux kernel treats each Android App as 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.

3. 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

4. Example Content Providers
Contacts
MediaStore
Bookmarks
User dictionary
Settings

5. Content Provider APIs Client Content Provider Provider Application
Data

6. Content Provider Intro
You must extend the ContentProvider class to create your content provider.
E.g.
public class KbContentProvider extends ContentProvider { // }

7. Content URI Used to specify a particular content provider Four Parts:
Scheme: For providers is always content://
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

8. Content URI
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
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.

9. 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.

10. 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.

11. Content Types First defined in RFC 1049 and refined in RFC 2045.
Consists of a type and a subtype. Eg. image/png

12. 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.

13. 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.

14. 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 directory-based
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

15. Example Content Resolver
Query operation on UserDictionary
Here are the parameters to the method
Returns a Cursor object that can be used to traverse the returned records.
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
selectionArgs
The binding parameters to the previous selection argument
sortOrder
If the result should be ordered you must use this argument to determine the sort order

16. Query Code Snippett 1 ContentResolver resolver = getContentResolver();
2 String[] projection = new String[]{BaseColumns._ID, UserDictionary.Words.WORD};
3 Cursor cursor =
resolver.query(UserDictionary.Words.CONTENT_URI,
projection,
null,
null,
null);
9 if (cursor.moveToFirst()) {
10 do {
long id = cursor.getLong(0);
String word = cursor.getString(1);
// do something meaningful
14 } while (cursor.moveToNext());
15}

17. Insert Snippet Type Name Usage URI 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);

18. Delete Code Snippet 1 long noDeleted = resolver.delete
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
(Words.CONTENT_URI,
Words.WORD + " = ? ",
new String[]{"Zaphod"});

19. Update 1 values.clear(); 2 values.put(Words.WORD, "Zaphod");
3 Uri uri = ContentUris.withAppendedId(Words.CONTENT_URI, id);
4 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

20. Contract classes are not included automatically with a provider
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.

21. 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.

22. 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.

23. 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

24. References