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Learn about Android Content Providers and SQLite

Scott A. ThisseMarch 20, 2012

Tampa Bay Android Developers Group

March 20, 2012 Tampa Bay Android Developers Group 2 of 32

Learn about Android Content Providersand SQLite

● What are they?

● How are they defined?

● How are they called?

● What do they return?

● SQLite


What Are They?

● Mechanism used to encapsulatedata into services

● Required when sharing data between apps

● Use REST-like URIs


How Are They Defined?

● Registered in AndroidManifest.xml

● Name is called an authority

● 3rd Party ones have FQNs

● Example:<provider

android:name="MyProvider"android:authorities="org.tbadg.MyProvider" />


How Are They Called?

● URIs are used

● Authority is used as a base name similar to how a domain name is used

● content:// is used as the scheme

● URI can identify an individual itemor an entire collection


How Are They Called?

● Input parameters are embedded in URI

● Each URI path segment must be predefined, documented, and interpreted by the provider

● Examples:

content://org.tbadg.MyProvider/content://contacts/people/content://contacts/people/13/


What Do They Return?

● Data returned as an Android cursor

● Callers expected to knowstructure of the returned data

● Returned data structured witha predefined MIME type

● MIME type returned for a given URI if requested via getType()


MIME Types

● Work similar as they do in HTTP

● MIME type returned as 2-part stringin the form <type>/<subtype>

● Type part for indivual items is alwaysvnd.android.cursor.item

● Type part for collections is alwaysvnd.android.cursor.dir


MIME Types

● Subtypes are more flexible

● Prefix with vnd for nonstandard,vendor-specific types

● Examples:vnd.android.cursor.item/vnd.tbadg.info

vnd.android.cursor.dir/vnd.tbadg.info


Accessing Data

● To reiterate, all access is thru URIs

● Base URIs (and columns) are usuallydefined with Java constants

● Easiest access is via managed query

● Built-in data requires a permissionsentry in AndroidManifest.xml


Managed Query

● Takes 5 parameters:● Base URI● Optional Array of properties (columns)● Optional Constraint clause (where)● Optional replacement values● Optional sort statement

● Returns a Cursor object


Managed Query Examples

● With URI based constraint:Cursor cur = managedQuery(“com.someprovider.app/entries/13”, null, null, null, null);

● Without constraints or sort:Cursor cur = managedQuery(android.provider.Browser.BOOKMARKS_URI, null, null, null, null);

● With a property (columns) array:… new String[] {"title"}, null, null, null);


Managed Query Examples (cont)

● With constraints (where) clause:… null, Browser.BookmarkColumns.BOOKMARK + " = 1", null, null);

● With replacement value:… null, "bookmark = ?", new String[] {"1"}, null);

● With sort statement:… null, null, null, "bookmark ASC title DESC");


Cursors

● Need to know names and type of columns

● Columns are identified by number in methods

● Random access collection of data rows

● Use moveToFirst() first and then moveToNext() and isAfterLast()to navigate thru data


Inserts, Updates, Deletes (oh my)

● Handled via a ContentResolver and a ContentValues dictionary

● Populate ContentValues with row'snew or changed values, then

● Call appropriate ContentResolver method

● Example:ContentValues cv = new ContentValues();

ContentResolver cr = getContentResolver();

Uri uri = cr.insert(SOME_PROVIDER_URI, cv);


Extending/Building Content Providers

● Future presentation(s) will show extending and building custom content providers

● See references for assistance before then


Live Example

● AndroidManifest.xml

● main.xml

● strings.xml

● ContentProviders.java


AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.tbadg" android:versionCode="1" android:versionName="1.0">

<uses-sdk android:minSdkVersion="7" /> <uses-permission android:name="com.android.browser.permission.READ_HISTORY_BOOKMARKS" />

<application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".ContentProviders" android:label="@string/app_name"> <intent-filter> <category android:name="android.intent.category.LAUNCHER" /> <action android:name="android.intent.action.MAIN" /> </intent-filter> </activity> </application></manifest>


main.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent">

<LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="wrap_content"> <ToggleButton android:id="@+id/bookmarks" android:layout_width="0dp" android:layout_weight="33" android:layout_height="wrap_content" android:textOn="@string/show_bookmarks_str" android:textOff="@string/noshow_bookmarks_str" android:onClick="onClick"> </ToggleButton>

continued...


main.xml (cont)

...continued

<ToggleButton android:id="@+id/history" android:layout_width="0dp" android:layout_weight="33" android:layout_height="wrap_content" android:textOn="@string/show_history_str" android:textOff="@string/noshow_history_str" android:onClick="onClick"> </ToggleButton>

<ToggleButton android:id="@+id/sort" android:layout_width="0dp" android:layout_weight="33" android:layout_height="wrap_content" android:textOn="@string/sorted_str" android:textOff="@string/unsorted_str" android:onClick="onClick"> </ToggleButton>

</LinearLayout>

continued...


main.xml (cont)

...continued

<TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/output_str" />

<ScrollView android:layout_width="fill_parent" android:layout_height="wrap_content">

<TextView android:id="@+id/output" android:layout_width="fill_parent" android:layout_height="wrap_content" />

</ScrollView></LinearLayout>


strings.xml

<?xml version="1.0" encoding="utf-8"?><resources> <string name="app_name">ContentProviders</string> <string name="show_bookmarks_str">Bookmarks</string> <string name="noshow_bookmarks_str">No Bookmarks</string> <string name="show_history_str">History</string> <string name="noshow_history_str">No History</string> <string name="sorted_str">Sorted</string> <string name="unsorted_str">Unsorted</string> <string name="output_str"><b><u>Output:</u></b></string></resources>


ContentProviders.javapackage org.tbadg;

import android.app.Activity;import android.database.Cursor;import android.os.Bundle;import android.provider.Browser;import android.view.View;import android.widget.TextView;import android.widget.ToggleButton;

public class ContentProviders extends Activity {

// Some handles to UI components: TextView _outputTvw = null; ToggleButton _bookmarksBtn = null; ToggleButton _historyBtn = null; ToggleButton _sortBtn = null;

@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main);

// Set up UI component handles: _outputTvw = (TextView)findViewById(R.id.output); _bookmarksBtn = (ToggleButton)findViewById(R.id.bookmarks); _historyBtn = (ToggleButton)findViewById(R.id.history); _sortBtn = (ToggleButton)findViewById(R.id.sort); }

continued...


ContentProviders.java (cont)

...continued

public void onClick(View v) { String where = null; String sort = null;

// Reset the output: _outputTvw.setText(null); // Determine (a bit redundantly) the data wanted: if (_bookmarksBtn.isChecked()) if (_historyBtn.isChecked()) // Both wanted where = null; else // Just bookmarks where = Browser.BookmarkColumns.BOOKMARK + " = 1"; else // Just history if (_historyBtn.isChecked()) where = Browser.BookmarkColumns.BOOKMARK + " <> 1"; else // neither return; continued...


ContentProviders.java (cont)

...continued

// Determine whether to sort the output (via the query): if (_sortBtn.isChecked()) sort = Browser.BookmarkColumns.TITLE + " ASC"; else sort = null;

// Get the data from the browser content provider: Cursor cur = managedQuery(android.provider.Browser.BOOKMARKS_URI, null, where, null, sort); int titleIndx = cur.getColumnIndex(Browser.BookmarkColumns.TITLE);

// Walk thru the data and add it to the output: cur.moveToFirst(); while (!cur.isAfterLast()) { _outputTvw.append(cur.getString(titleIndx) + "\n"); cur.moveToNext(); } } }


Screenshot


SQLite

● Most common CP data store

● Installed on all Android devices

● Open source, embedded database

● Databases implemented as flat-files

● Executable is named sqlite3


Some Built-in Databases

● AlarmClock

● Browser

● CallLog

● Contacts

● MediaStore

● Settings


Some Useful SQLite Commands

● .mode column – enable column output

● .headers on – enable column headers

● .output <file> – redirect output to file

● .output stdout – redirect output to screen

● .show – display current options

● .help – display command help


Some Useful SQLite Commands (cont)

● .schema – display all database info

● .tables – display table info

● .indexes – display index info

● .dump – export database objects

● .read <file> – import dumped data

● .exit – exit the interpreter


Q & A

Questions?


References

Allen, G. and Owens M. (2010). The Definitive Guide to SQLite, Second Edition. New York, New York: Apress

Content Providers (n.d.). Retrieved March 8, 2012, from http://developer.android.com/guide/topics/providers/content-providers.html

Komatineni, S. et al. (2011). Pro Android 3. New York, New York: Apress

Murphy, M. (2012). The Busy Coder's Guide to Advanced Android Development. Retrieved March 8, 2012 from http://commonsware.com

http://developer.android.com/guide/topics/providers/content-providers.html

http://commonsware.com/

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