STORAGECONTENT PROVIDER

Storage

Internal(Flash Memory)

External(SD card)

Linux OS

File System

..\AppData\Local\Android\sdk\platform-tools\adb

Exploring the file system

File System

Android allows to persists application data via the file system. For each application the Android system creates a data/data/[application package] directory

Storage options• SharedPreference

• Small amount of data• Key-value pairs• Private to an Activity or• Shared among Activities

• Internal storage• Small to medium amount of data• Private to the application

• External storage• Not private data (songs, video files)

• Database (SQLite)• Structured data• Private to the application

Shared Preferences• Persistent map of primitive types

• Automatically persisted among application sessions

• Activity.getPreference(mode)• Returns: SharedPreference is associated to the activity

• not accessible from other activities in the same package• Mode used to create the preference (private is recommended)• Returns a SharedPreference object

• Context.getSharedPreference(Name,mode)• Returns: SharedPreference associated to the package• Name of the file used to store the preferences• Mode

Writing/Reading SharedPreference• Call SharedPreference.edit() method

• Returns an SharedPreference.Editor instance

• Call put methods to add values• Call Editor.commit() to make value persistent• Call get methods to retrieve values

• SharedPreferenceFragment allows for using a simple framework to set preferences

Example

File• Represented by the File class (java.io package)• File can be internal…

• Internal flash memory in the device• Usually used for private small amount of data

• …or external• SD Card• Larger non-private storage area

• A file can be opened for reading or writing…• Standard java way to use the file

File• External file are stored in removable storage (i.e., SD

card)• Check for the presence of the storage before accessing

any file• Environment.getExternalStorageState()

• State: Mounted, ReadOnly, etc.

• Environment is a class (java.os package) providing info about environment variables.

• Requires permission in the manifest file

SQLite• Used for structured information• Small foot-print relational DB

• It supports ACID transaction

• Implements most of the SQL92 standard• Stores data into a text file

• /data/data/<package-name>/databases/

• Options to create in-memory DB• The adb tool has sql3 command to show the db

Content Provider• A content provider manages access to a central repository

of data• A content provider presents data to external applications

as one or more tables that are similar to the tables found in a relational database.

• A row represents an instance of some type of data the provider collects, and each column in the row represents an individual piece of data collected for an instance

• The data itself can be stored in an SQlite database, on the file system, in flat files or on a remote server.

• Permissions are required to use a content provider

Content providerA content provider is identified by URI (content://authority/path/id)It exposes a set of standard operationsAccessed through intent or contentResolverAccessed from other processes

Intent ‘bus’

Intent-Filter

Activity

<uses-permission>

Content Provider’s URI• content://authority/path/id

• Content = means one want to access a content provider• Authority = name of the content provider• Path = specific data set (table) in the content provider• Id = specific row in the table (option)

• For example:• Content://com.android.contacts/contacts

Accessing a Content provider• Clients access to a content provider through a

ContentResolver• ContentResolver allows access to the provider through a

set of db-like methods• Insert,Update,Query,Delete

Main content providers• AlarmClock

• Alarms to fire• CallLog

• contains information about placed and received calls• Contact provider

• Stores all information about contacts.• Calendar provider

• Data stored in the ‘calendar’ (events, etc.)• Media Provider

• contains meta data for all available media on both internal and external storage devices.

• Settings• global system-level device preferences

• User Disctionary• user defined words for input methods to use for predictive text input.

• Full list: adb shell dumpsys (look for Content Provider)

ContentResolver query• ContentResover.query () allows to access specific data

• Similar to an SQL query• Content URI• Columns to retrieve – String []• SQL selection pattern - String• SQL selection arguments – String []• Sort Order - String

• Returns a Cursor object

CursorLoader• It is a class that uses an AsyncTask to perform the query

in background• To use a CursorLoader one has to implement the

LoaderCallbacks interfece

Insert a row

Other methods• ContenteResolver.update(

• URI• ContentValues• SQL selection pattern – String• SQL selection args – String []• Return number of rows updated

• ContentResolver.delete()• URI• SQL Selection pattern – String• SQL Selection args. – String []• Returns number of row deleted

Creating a ContentProvider• Implement a storage system for the data

• For example an SQL DB, but other storage options are good as well

• Define a contract Class• ContantProvider subclass

• Implements update(), etc. methods

• Define manifest file• <provide> tag• Contains authoriries attribute

Example: Contact Provider• Maintains three type of data about a person, each of one

corresponds to an entry into a different table• ContactsContract.Contacts

• A row represents a summary of info about a person • Some column: PHOTO_ID,PHOTO_URI

• ContactsContract.RawContacts• ContactsContracy.Data

Example: Google calendar Provider

Interface(rest,etc)

Calendar’s data model

Accessing Content Provider via Intents

Loading data from the project• A file is also considered a raw resourse• An interesting application is to display an html page into a

webview

WebView• Allows to host a web page • The page can be loaded from internet or stored locally• Requires INTERNET permission in the manifest • It is based on WebKit engine

• Navigate back and forward • Zoom in and out• Load data, etc..

• It may execute javascript code• By default it is disabled

Using web view• An interesting point is that data can be loaded from a local

file (or even passed as a string)• browser.loadData (“<html> <body> Hello!</body></html>”,”UTF-8”);• browser.loadUrl ("file:///android_asset/my_local_webpage1.html");

Binding JavaScript code to Android code

• It is possible to create interfaces between JavaScript code and client-side Android code.

• In other words, JavaScript code can call a method in the Android code

• This is very powerful but it’s also a source of risk • One can write application using JS and HTML (this is

what PhoneGap does)

Binding JavaScript code to Android code

• Public methods are seen as JS function

• The object that is bound to your JavaScript runs in another thread and not in the thread in which it was constructed.

• Only simple data can be passed

• JSON can be useful in this respect

Android Code

HTML + JS..

Android.test()

Add Interface (C,“Android”)

Android.test();

Class Ctest

public method

Navigation functions