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

STORAGE CONTENT PROVIDER

Storage File System Linux OS Internal External (Flash Memory) (SD card) ..\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 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 <uses-permission> Activity Intent-Filter Intent ‘bus’

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 Add Interface (C,“Android”) HTML + JS .. Android.test() Android Code Android.test(); • Public methods are seen as JS function test Class C • The object that is bound to your JavaScript runs in another thread and not in the thread in which it was constructed. public method • Only simple data can be passed • JSON can be useful in this respect

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