STORAGE CONTENT PROVIDER Storage File System Linux OS Internal - - PowerPoint PPT Presentation

STORAGE CONTENT 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
• f 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 provider

A content provider is identified by URI (content://authority/path/id) It exposes a set of standard operations Accessed through intent or contentResolver Accessed 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 C test

public method

Navigation functions