Download Week 6 Power Point Slides

The Android File System
• Onboard: Linux Architecture
• User privileges
– Initially quite limited; some directories hidden
– Rooting gives users super user access
o Procedure is different for different devices
o Destroying the operation of the device: bricking
• Onboard data: Applications have their reserved storage areas (sandbox)
• External data
– SD card or USB connection
– Public shared: /mnt/sdcard/
– Writing to external storage has no security protection
Managing Data (Alternatives)
• Application Direct Access: Read only from res/raw or assets directories
• Web-based: Interact through web-URLs to access cloud-based data
• Direct File I/O: Read/write files onboard or on SD cards
– Use Standard Java stream and Random Access File classes
– Restriction: Onboard file I/O restricted to application sandbox
– Restriction: SD card writes requires access permission
• Preferences: Key/Value pairs of data
• Database Tables: Use the built-in SQL-Lite database facility
• Increase functionality:
– Content Providers: expose data to other applications
– Services: background processes that run detached from any view
Application Direct Access
• Static application files
– Custom codecs that are not widely supported
– XML-based configuration data
• Store either in res/raw or in assets
– res/raw enables creating sub-directories for specific device configurations
– Files stored either in res/raw or in assets are not pre-compiled by Android.
However file names in res/raw are compiled into resource access codes.
– Files stored directly in the application are read-only and cannot be modified
– Access using standard Java I/O operations
InputStream is = app.getResources().openRawResource(R.raw.foo);
in = BufferedReader in = new BufferedReader(new InputStreamReader(is)));
InputStream rawRes = context.getAssets().open("foo.bar");
Reader r = new BufferedReader(new InputStreamReader(rawRes, "UTF8"));
Note: Use lower case alphanumeric to name files in res/raw
Downloading Files
• Downloading quickly degrades battery life
• Solutions
– Pre-fetch: A single large download has less impact
than multiple smaller downloads
– Reuse existing connections rather than
reestablishing them
– Schedule regular downloads at the longest
intervals that are possible
– Bundle non-time sensitive requests together
Reading from the Web
public byte[] getUrlBytes(String urlSpec) throws IOException {
URL url = new URL(urlSpec);
HttpURLConnection c = (HttpURLConnection)url.openConnection();
try{ ByteArrayOutputStream out = new ByteArrayOutputStream();
InputStream in = connection.getInputStream();
if (c.getResponseCode()!=HttpURLConnection.HTTP_OK) {
throw new IOException(c.getResponseMessage() +
": with " + urlSpec);
}
int bytesRead;
byte[] buffer = new byte[1024];
while ((bytesRead = in.read(buffer)) > 0)
{ out.write(buffer, 0, bytesRead); }
out.close();
return out.toByteArray();
} finally { c.disconnect(); }
}
Parsing JSON
JavaScript Object Notation: common format for transferring Internet data
{ "photos"; { "page": 1, "pages": 10, "perpage":100, "total": 1000,
"photo": [
{ "id": "9452133594",
"owner": "44494372@N05",
“secret:“, "d6d20af93e", "server": "7365",
"farm": "8",
"title": "Low and Wisoff at Work",
"ispublic": "1",
"isfriend": "0",
"isfamily": "0"
}, … ]
}, "stat": "ok“ }
Get id for the first item in the array (where index == 0)
getJSONObject("photos")  getJSONArray("photo") 
getJSONObject(index)  getString("id")
Background Tasks
1. Problem: Android terminates applications that do computationally
intense operations on the user interface threads
2. First solution: Create a background thread that does the operations
and notifies the User thread when done.
Disadvantage: requires low level code to implement
3. Second solution: Extend Async task that runs in a background thread
and handles the details of notifying the user level thread.
Disadvantage: The user interface is notified once after completion.
4. Third solution: Use a download handler that notifies the user level
thread multiple times. For example, when each image of a list is
downloaded.
Disadvantage: More flexibility comes at the cost of more complexity
5. Fourth solution: Use the API for one of the download applications
Disadvantage: Less flexible
Async Task to download a File
<type of input, type of progress, type of results>
class Fetch extends AsyncTask<Void,Void,List<GalleryItem>> {
@Override List<GalleryItem> doInBackground(Void... params) {
return new FlickrFetchr().fetchItems();
}
@Override void onPostExecute(List<GalleryItem> items) {
mItems = items; setupAdapter(); }
Download Using Download Manager
DownloadManager m= (DownloadManager)getSystemService(Context.DOWNLOAD_SERVICE);
long myReference = m.enqueue(new Request(Uri.parse(R.string.webLoc)));
BroadcastReceiver receiver = new BroadcastReceiver()
{ @Override public void onReceive(Context context, Intent intent)
{ long reference = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
if (myReference == reference)
{ Query query = new Query();
Cursor cursor = downloadManager.query(query.setFilterById(reference));
if (cursor.moveToFirst())
{ int fileX = cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_FILENAME);
int uriX = cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI);
String fileName = cursor.getString(fileX), fileUri = cursor.getString(uriX);
// TODO Do something with the file.
}
cursor.close();
Note: The cursor object contains
} } };
information about downloaded files
registerReceiver(receiver,
new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE) );
Listen for Downloaded Files
<receiver android:name=".DownloadReceiver"
android:exported="true" // Receive from other applications
android:icon="@drawable/download_icon" > // For notification
<intent-filter>
<action android:name="android.intent.action.DOWNLOAD_COMPLETE"/>
</intent-filter></receiver>
IntentFilter filter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
registerReceiver(receiver,
new BroadcastReceiver()
{ @Override public void onReceive(Context context, Intent intent)
{ String id = DownloadManager.EXTRA_DOWNLOAD_ID;
long[] references = intent.getLongArrayExtra(id); // Array of downloaded file ids
for (long reference : references)
{ String mime = getMimeTypeForDownloadedFile (reference);
{
// Handle files that this activity recognizes.
}
} } }, filter);
Specifying Download Locations
Note: We cannot download to internal storage using DownloadManager
External Storage: Removable storage (ex: SD card) or internal non-removable
storage. External storage files are public and user modifiable via USB storage
• Download cache: Shared download cache with system generated name
• Overriding the download location requires:
<uses-permission android:name =
"android.permission.WRITE_EXTERNAL_STORAGE" />
• To designate an arbitrary path in external storage
Request request = new Request(uri); // DownloadManager.Request
request.setDestinationUri(Uri.fromFile(f));
• To designate a standard external download folder for the application
request.setDestinationInExternalFilesDir(this,
Environment.DIRECTORY_DOWNLOADS, fileName);
• To designate location which shares with music players
request.setDistinationInExternalPublicDir
(Environment.DIRECTORY_MUSIC, fileName);
SD Card File IO
• SD Card path: getExternalStorageDirectory()
• How: Use standard Java File I/O
• Notes:
– Manifest: "android.permission.WRITE_EXTERNAL_STORAGE"
– Application manifests can set preference to SD Card installation
– Check SD Availability in Java:
Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)
• Convention: write to /Android/data/<package_name>/files/
• Example
File sdCard = Environment.getExternalStorageDirectory();
File dir = new File (sdcard.getAbsolutePath()
+ " /Android/data/<package_name>/files/ ");
dir.mkdirs(); // Make directories with missing parents.
File file = new File(dir, "filename"); // Instantiate a file object
FileOutputStream f = new FileOutputStream(file); // Open for writing
Writing to Internal Storage
• Writing to internal storage
– Each application has a designated directory to which to write files
– There is a maximum storage amount, varying per device
– Flags exist to control inter-application access
•
•
•
•
MODE_PRIVATE - No access for other applications
MODE_WORLD_READABLE - Read access for other applications
MODE_WORLD_WRITABLE - Write access for other applications
MODE_WORLD_READABLE | MODE_WORLD_WRITABLE - Read / Write access
• Open file for writing
new BufferedWriter(
new OutputStreamWriter(
openFileOutput(fileName, MODE_PRIVATE)));
Onboard File I/O
• Write to a designated place for each application
– Where: /data/data/package/files/ using onboard storage
– How: Use standard java.io classes, with relative, not absolute, paths
– Applications can:
o Write into its application directory
o Create subdirectories
o Give read/write permissions to other applications
(MODE_PRIVATE, MODE_WORLD_READABLE | MODE_WORLD_WRITABLE)
• Android Helper classes in the Context object
– getDir(String fileName, int permissions): Creates or access directory
– getFilesDir(): Get absolute path to application directory
– getCacheDir(): Get non-permanent temporary storage directory
– openFileInput(String fileName): Open a file for input
– openFileOutput(String fileName, int permissions): Create a new file
Note: There is also a sharedPreferences directory for preferences,
a databases directory for SQLite tables, and a cache directory
Copy File from Server
public void DownloadFile(String fileURL, String fileName)
{ try { HttpURLConnection c = (HttpURLConnection) fileURL.openConnection();
c.setRequestMethod("GET");
c.setDoOutput(false); // True for “POST” with intent to send to server
c.connect();
// Establish connection with server
InputStream in = c.getInputStream(); // Ready to read
}
}
File root = Environment.getExternalFilesDir(null); // Application area
// Prepare output stream
FileOutputStream out = new FileOutputStream(new File(root, fileName));
byte[] buffer = new byte[1024];
int len = 0; // Note the buffer overflow possibility
while ((len = in.read(buffer)) > 0) { out.write(buffer, 0, len); } // Write block
f.close();
} catch (Exception e) { Log.d("Downloader", e.getMessage()); }
Preferences
• Initial Purpose:
– Persistent storage for user options
– Analogous to cookies in Web-based applications
• More General Purpose:
– Maintains the application state across terminations and restarts
– Provides mechanism for applications to persistently store
additional data without using SQL or Files
• Preferences Framework
1. Define preferences
2. Display settings
3. Persist user selections
Accessing Shared Preference Data
// getPreferences is a method in the Activity class
SharedPreferences prefs = getPreferences(Activity.MODE_PRIVATE);
int intValue = prefs.getInt("IntKey", 22);
long longValue = prefs.getLong("LongKey", 0);
String name = prefs.getString("NameKey", "");
int floatValue = prefs.getFloat("FloatKey", 0.0);
int booleanValue = prefs.getBoolean("BoolKey", false);
Set<String> set = prefs.getStringSet("SetKey", 22);
Map<String, ?> prefs.keysAndValues = getAll();
Note: The second argument is the default if the
key was not previously stored
Modifying SharedPreference Data
SharedPreferences preferences = getPreferences(Activity.MODE_PRIVATE);
// or getSharedPreferences("fileName");
SharedPreferences.Editor editor = preferences.edit();
editor.putInt("IntKey", 22);
editor.putLong("LongKey", 0);
editor.putString("NameKey", "");
editor.putFloat("FloatKey", 0.0);
editor.putBoolean("BoolKey", false);
editor.commit();
Notes:
1. puts can be chained: editor.putInt(“intKey”, 22).putLong(“LongKey”, 0);
2. editor.apply() works asynchronously, editor.commit() is synchronous
3. editor.clear() erases all of the preference keys
4. editor.remove(“Key”) deletes a preference
5. Shared preferences use a file name for multi-activity sharing
Preference Views
• Preference Screen


•
The view on the left
View on the right appears
When the user touches after
preference screen
Selection Screen


Modal Dialog on the right
Saves selection and disappears
after a user selection
Step 1: Defining Preferences
XML Listing (in res/xml) for the preferences shown on the previous screen
<?xml version="1.0" encoding="utf-8"?> <!-- /res/xml/flightoptions.xml -->
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
android:key="FlightOptionPreference"
android:title="@string/PrefTitle" >
<ListPreference android:key="@string/SelectedSortOption"
android:title="@string/ListTitle" android:summary="@string/ListSummary"
android:entries="@array/FlightSortOptions"
android:entryValues="@array/FlightSortValues"
android:dialogTitle="@string/ChooseFlightOptions"
android:defaultValue="@string/SortDefaultValue" />
</PreferenceScreen>
public class FlightPreferences extends PreferenceActivity
{ @Override protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.flightoptions);
} }
Define Strings in res/values
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name=“FlightOptionPreference">Preferences Demo</string>
<string name="PrefTitle">My Preferences</string>
<string name="ListTitle">Flight Options</string>
<string name="ListSummary">Set Search Options</string>
<string-array name="FlightSortOptions">
<item>Total Cost</item><item># of Stops</item><item>Airline</item>
</string-array>
<string-array name="FlightSortValues">
<item>0</item><item>1</item><item>2</item>
</string-array>
<string name="ChooseFlightOptions">Choose Flight Options</string>
<string name="SortDefaultValue">1</string>
<string name="SelectedSortOption">Selected_Sort_Option</string>
</resources>
Manifest
<?xml version="1.0" encoding="utf-8"?> <!-- AndroidManifest.xml -->
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.syh" android:versionCode="1" android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/AppName">
<activity android:name=".MainActivity" android:label="@string/AppName">
<intent-filter><action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".FlightPreferences" android:label="@string/PrefTitle">
<intent-filter><action android:name=".FlightPreferences" />
<category android:name="android.intent.category.PREFERENCE" />
</intent-filter>
</activity></application><uses-sdk android:minSdkVersion=“15" /></manifest>
Define Main Android Activity
// This is MainActivity.java
@Override public void onCreate(Bundle savedInstanceState)
{ super.onCreate(savedInstanceState);
setContentView(R.layout.main); // Assuming there is a TextView layout
tv = (TextView)findViewById(R.id.text1);
setOptionText(); // Helper method to get user preference and adjust view
}
@Override public boolean onCreateOptionsMenu(Menu menu)
{ MenuInflater inflater = getMenuInflater();
// Inflate main menu XML with link to preference option
inflater.inflate(R.menu.mainmenu, menu);
return true; // Menu is now active
}
Main Activity Selection Responses
@Override public boolean onOptionsItemSelected (MenuItem item)
{ if (item.getItemId() == R.id.menu_prefs)
{
Intent intent = new Intent().setClass(this, .FlightPreferences.class);
this.startActivityForResult(intent, 0); // Second parameter is for a switch in listener
} else if (item.getItemId() == R.id.menu_quit) { finish(); }
return true;
// Start preference menu when its item is selected
}
@Override public void onActivityResult(int reqCode, int resCode, Intent data)
{ super.onActivityResult(reqCode, resCode, data);
SharedPreferences prefs = getDefaultSHaredPreferences(this);
String key = this.getResources().getString(R.string.SelectedSortOption);
String default = this.getResources().getString(R.string.SortDefaultValue);
String pref = prefs.getString(key , default);
String[] optionText = this.getResources().getStringArray(R.string.FlightSortOptions);
tv.setText("option = " + pref + " (" +optionText[Integer.parseInt(pref)] + ")");
}
CheckBoxPreference
(/res/xml/chkbox.xml)
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen
xmlns:android ="http://schemas.android.com/apk/res/android"
android:key="flight_columns_pref">
<CheckBoxPreference android:key="show_airline_column_pref"
android:title="Airline" android:summary="Show Airline column" />
<CheckBoxPreference android:key="show_departure_column_pref"
android:title="Departure" android:summary="Show Departure column" />
<CheckBoxPreference android:key="show_arrival_column_pref"
android:title="Arrival" android:summary="Show Arrival column" />
<CheckBoxPreference android:key="show_total_travel_time_column_pref"
android:title="Total Travel Time“ android:summary="Show Total Travel Time column“
/>
<CheckBoxPreference android:key="show_price_column_pref"
android:title="Price" android:summary="Show Price column" />
</PreferenceScreen>
Note: For Radio Buttons, use the List Preference
Using Check Box Preferences
// CheckBoxPreferenceActivity.java
import android.os.Bundle;
import android.preference.PreferenceActivity;
public class CheckBoxPreferenceActivity extends PreferenceActivity
{
@Override protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.chkbox);
}
}
// Access preference in an activity
SharedPreferences prefs = getSharedPreferences("fileName");
Boolean option = prefs.getBoolean("show_price_column_pref", false);
EditTextPreference
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android=http://schemas.android.com/apk/res/android
android:title=“Set Package Name"
android:summary="Set the package name for generated code">
<EditTextPreference android:key="package_name_preference"
android:title="Set Package Name" android:dialogTitle="Package Name"
android:summary="Set the package name for generated code" />
</PreferenceScreen>
Categories of Preferences
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
android:key="using_categories_in_root_screen" android:title="Categories"
android:summary="Using Preference Categories">
<PreferenceCategory
android:key="meats_category" android:title="Meats" android:summary="Meat preferences">
<CheckBoxPreference android:key="fish_selection_pref" android:title="Fish"
android:summary="Fish is great for the healthy" />
<CheckBoxPreference android:key="chicken_selection_pref" android:title="Chicken"
android:summary="A common type of poultry" />
<CheckBoxPreference android:key="lamb_selection_pref" android:title="Lamb"
android:summary="Lamb is a young sheep" /></PreferenceCategory>
<PreferenceCategory
android:key="vegi_category" android:title="Vegetables" android:summary="Vegetable preferences">
<CheckBoxPreference android:key="tomato_selection_pref" android:title="Tomato "
android:summary="It's actually a fruit" />
<CheckBoxPreference android:key="potato_selection_pref" android:title="Potato"
android:summary="My favorite vegetable" /></PreferenceCategory></PreferenceScreen>
Purpose: Provide titles to groups of similar preferences
Preference Fragments
• Android versions 3.0 and newer recommend using fragments
for preferences instead of activities
• Check Android Version:
if (Build.VERSION.SKK_INT<Build.VERSION_CODES.HONEYCOME)
{ /* Use preference activity approach */ }
else { /* Use preference fragment approach */ }
• Implementation Steps
1. Define preference screens in XML (as shown on previous slides)
2. Add PreferenceFragment to the activity using the
FragmentManager
3. Create the PreferenceFragment class
Preference Fragment in an Activity
public class PreferenceFragmentActivity extends Activity
{ @Override
public void onCreate(Bundle savedInstanceState)
{ super.onCreate(savedInstanceState);
setContentView(R.layout.main);
FragmentManager manager = getFragmentManager();
FragmentTransaction trans = manager.beginTransaction();
MyFragment fragment = new MyFragment();
trans.replace(android.R.id.content, fragment1);
trans.addToBackStack(null);
trans.commit();
}
}
Note: Don’t add the fragment to the application manifest
Preference Fragment Class
public class MyFragment extends PreferenceFragment
{ @Override public void onCreate(Bundle savedInstanceState)
{ super.onCreate(savedInstanceState);
// configure the preferences from an XML file
addPreferencesFromResource(R.xml.preferences);
PreferenceManager manager = getPreferenceManager();
SharedPreferences shared = manager.getSharedPreferences();
shared.registerOnSharedPreferenceChangeListener(this);
}
onSharedPreferenceChanged(SharedPreferences pref, String key)
{ /* Handle preference change here */ }
}
SQLite
• Android SQLite:
–
–
–
–
Lightweight database system
Standards-compliant
Single Tier (no server involved)
Open source
• Standard SQL queries
“SELECT ID, CITY, STATE FROM STATION WHERE LAT_N > 39.7;”
• Application content providers provide
– Standard interface to SQL tables to other applications
– For application private tables, content providers are not needed
Steps to work with a database
• Define the Schema for an SQL table
• Use database helper to automatically create
or update the table
• Create a Cursor wrapper and add methods to
return appropriate objects
• Implement appropriate add, update, remove,
and get methods in the model
Define Schema
public class CrimeDbSchema {
public final static class CrimeTable {
public static final String NAME = "crimes";
public static final class Cols
public static final String
public static final String
public static final String
public static final String
}
}
}
{
UUID = "uuid";
TITLE = "title";
DATE = "date";
SOLVED = "solved";
DataBase Helper
• Purpose
–
–
–
–
Manage database creation and version management
Responsible for creating and upgrading an SQLite database
Defer database opening and updating to the first use
Avoids blocking application startup with compute intensive database
upgrades
– Contains methods for getWritableDatabase and
getReadableDatabase
– Simplifies Content Provider access to files
– Eliminates concern over whether the application was terminated
• Implementation
– Create a class that extends SQLiteOpenHelper
– Override onCreate() and onUpgrade() methods
DatabaseHelper
public class CrimeBaseHelper extends SQLiteOpenHelper {
private static final int VERSION = 1;
private static final String DATABASE_NAME = "crimeBase.db";
}
public CrimeBaseHelper(Context context) {
super(context, DATABASE_NAME, null, VERSION);
}
@Override public void onUpgrade
(SQLiteDatabase sqLiteDatabase, int i, int i1) {}
@Override public void onCreate(SQLiteDatabase db) {
db.execSQL("create table " + CrimeTable.NAME + "(" +
"_id integer primary key autoincrement, " +
CrimeTable.Cols.UUID + ", " +
CrimeTable.Cols.TITLE + ", " +
CrimeDbSchema.CrimeTable.Cols.DATE + ", " +
CrimeTable.Cols.SOLVED + ")"
);
}
To access: mDatabase = new CrimeBaseHelper
(context.getApplicationContext()).getWritableDatabase();
Helper Example (cont.) Upgrading the DB
Called when the version number in the constructor changes
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
db.execSQL("DROP TABLE IF EXISTS "+employees);
db.execSQL("DROP TABLE IF EXISTS "+depts);
db.execSQL("DROP TRIGGER IF EXISTS dept_id_trigger");
db.execSQL("DROP TRIGGER IF EXISTS dept_id_trigger22");
db.execSQL("DROP TRIGGER IF EXISTS fk_empdept_deptid");
db.execSQL("DROP VIEW IF EXISTS "+viewEmps);
onCreate(db);
}
SQLite View: Pre-packaged select statement
SQLite Trigger: Callback methods invoked to respond to database events
Note: The activity can respond to menu selections to insert, remove, and update rows
CursorWrapper
public class CrimeCursorWrapper extends CursorWrapper {
public CrimeCursorWrapper(Cursor cursor) {
super(cursor); }
public Crime getCrime() {
String uuidString
= getString(getColumnIndex(CrimeTable.Cols.UUID));
String title
= getString(getColumnIndex(CrimeTable.Cols.TITLE));
long date = getLong(getColumnIndex(CrimeTable.Cols.DATE));
int isSolved
= getInt(getColumnIndex(CrimeTable.Cols.SOLVED));
Crime crime = new Crime(UUID.fromString(uuidString));
crime.setTitle(title);
crime.setDate(new Date(date));
crime.setSolved(isSolved !=0 );
return crime;
}
}
Useful Supporting Methods
private static ContentValues getContentValues(Crime crime) {
ContentValues values = new ContentValues();
values.put(CrimeTable.Cols.UUID,
crime.getId().toString());
values.put(CrimeTable.Cols.TITLE, crime.getTitle());
values.put(CrimeTable.Cols.DATE,
crime.getDate().getTime());
values.put(CrimeTable.Cols.SOLVED, crime.isSolved()?1:0);
return values;
}
private CrimeCursorWrapper queryCrimes
(String whereClause, String[] whereArgs) {
Cursor cursor = mDatabase.query(
CrimeTable.NAME, null, // Columns; null selects all
whereClause, whereArgs,
null, /* Group by */ null, /* having */ null /* orderBy */
);
return new CrimeCursorWrapper(cursor);
}
Altering the Database
public void addCrime(Crime c) {
ContentValues values = getContentValues(c);
mDatabase.insert(CrimeTable.NAME, null, values);
}
public void updateCrime(Crime c) {
String uuidString = c.getId().toString();
ContentValues values = getContentValues(c);
mDatabase.update(CrimeTable.NAME, values,
CrimeTable.Cols.UUID + " = ?",
new String[] { uuidString });
}
public void deleteCrime(Crime c) {
String uuidString = c.getId().toString();
mDatabase.delete(CrimeTable.NAME,
CrimeTable.Cols.UUID + " = ?",
new String[] { uuidString });
}
Retrieving from the Database
public Crime getCrime(UUID id) {
CrimeCursorWrapper cursor =
queryCrimes(CrimeTable.Cols.UUID + " = ?",
new String[] {id.toString() } );
try { if (cursor.getCount() == 0) { return null; }
cursor.moveToFirst();
return cursor.getCrime();
} finally { cursor.close() }
}
public List<Crime> getCrimes() {
List<Crime> crimes = new ArrayList<>();
CrimeCursorWrapper cursor = queryCrimes(null, null);
try { cursor.moveToFirst();
while (!cursor.isAfterLast())
{ crimes.add(cursor.getCrime());
cursor.moveToNext(); }
} finally { cursor.close() }
return crimes;
}
Store Files in an SQLite Database
Steps
1.
2.
3.
Create the SQLite table with a column called _data
Get a writeable output stream
Write the file to the reserved column name _data
I/O Example
ContentValues object
contains a set of key/values
//Use a content resolver to insert the record
ContentResolver contentResolver = activity.getContentResolver();
Uri newUri = contentResolver.insert(Notepad.Notes.CONTENT_URI, values);
//Use the content resolver to get an output stream directly
OutputStream outStream = contentResolver().openOutputStream(newUri);
writeFileToRecord(outStream);
outStream.close();
Note: The data is actually stored in a
separate area. The _data column contains
the Uri reference to the data
Content Provider Framework
•
•
•
•
•
•
•
An application registers its content provider using its manifest
The code for the content provider is written
An application requests a provider using the published MIME type
Android looks through the registered manifests for a match
The provider activity is launched to manipulate or return data
If more than one provider exists, the user selects the one to use
Query a content provider using the provider’s URI:
content://media/internal/images/,
content://media/external/images/,
content://contacts/people/
Creating a Provider
• Plan the Database
• Extend the ContentProvider class
• Fill in a variety of methods to be overloaded
– onCreate(): When the database is created
– onUpgrade(): When the database layout changes
– getType(): Return the MIME data type
– query(): Handle queries to the data
– insert(), delete(), and update() methods
• Register the provider in the manifest
Authorities
Purpose: Publish application SQL tables and data for external activity access
• Definition: An authority is a system unique manifest registered name. Authorities
are to Android what domain names are to the web
• Example:
<provider android:name="android.support.v4.content.FileProvider"
android:authorities="com.mydomain.fileprovider"
android:exported="false" android:grantUriPermissions="true">
...
</provider>
• Activity content provider access with a Uniform Resource Identifier (URI)
– Syntax: content://<relative path>
– Access book table: content://com.anroidbook.provider.BookProvider/books
– Access particular book:
content://com.anroidbook.provider.BookProvider/books/12
– grantURIPermission: All data accessible (true) or subsets of data accessible
– exported: Accessible by other applications
MIME Types
Purpose: Indicate a type of data that a content provider deals with
•
•
•
•
•
•
Definition: Industry standard way to indicate a particular data format
Syntax: Two text strings separated by slashes
First part (category): application, audio, image, text, video, etc
Second Part (codec): html, css, xml, pdf, rtf, etc.
Examples: text/htm, application/pdf, image/jpeg, audio/mpeg, etc.
Android MIME Types (Similar syntax as standard MIME types)
– First Part
o Access single items: vnd.android.cursor.item
o Access multiple items: vnd.android.cursor.dir
– Second Part: vnd.yourCompany.type
– Examples: vnd.android.cursor.dir/vnd.google.note
or vnd.android.cursor.item/vnd.google.note
MIME Types
Acronym: Multipurpose Internet Mail Extension
• Specifies the data type an activity can process
– Register in the AndroidManifest.xml file
– Example: "vnd.android.cursor.dir/vnd.google.note"
OR "vnd.android.cursor.dir/vnd.google.note"
• Sample Syntax: vnd.android.cursor.<opt>/vnd.company.type
–
–
–
–
–
vnd: non-standard type (vendor)
android.cursor: required for ContentProvider Manifest registrations
item: single record; dir: collection of records
google: company name
note: content type
• AndroidManifest.xml registration
<data android:mimeType="vnd.android.cursor.dir/vnd.google.note" />
Referring to a Content Provider
• URI and URL
– Uniform resource identifier (URI) Identifies the name of a resource, but not
necessarily information regarding its location
– Uniform resource Location (URL) is a URI, that identifies a resource location
– Text usage: URI for content providers; URL for referring to Web locations
• URI of a content provider
content://com.company.fooProvider/
content://com.acorns.provider.Lessons/
content://com.google.provider.NotePad/
• Note: Android provided shortcut URIs: contacts
• Refer to the notes SQLite notes table
for com.google.android.contacts
content://com.google.provider.NotePad/notes/
• Refer to the tenth note
content://com.google.provider/NotePad/notes/10
Register Content Providers
A well-defined interface to data for application access
• Register an authority using the AndroidManifest.xml file
– Definition: An authority is a registered name
– Analogy: authority is to an Android device what a domain name is
to the Internet
• Syntax: ( Using a package name minimizes redundancies on a system)
<provider android:name="fooProvider"
android:authorities="com.company.fooProvider" />
• Example:
<provider android:name=" com.acorns.LessonProvider"
android:authorities="com.acorns.provider.Lessons" />
• Another application example:
<provider android:name="NotePadProvider"
android:authorities="com.google.provider.NotePad" />
Provider Intent Filter
<activity android:name="NotesList" android:label="@string/title_notes_list">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<data android:mimeType="vnd.android.cursor.dir/vnd.google.note" />
</intent-filter><intent-filter>
<action android:name="android.intent.action.GET_CONTENT" />
<data android:mimeType="vnd.android.cursor.item/vnd.google.note" >
</intent-filter> </activity>
Content Resolver
Interact with a content provider
• Definition: A Content Resolver is an Android class that
matches the URI to an available Content Provider that can
handle the data
• Purpose: Separate provider (controller) from the data
(model), enabling multiple content providers to be available
to handle the same data types
• Access: Use a collection of method calls to insert, retrieve,
delete, update data records
• Example: (insert a new note into the notepad)
ContentResolver resolver = activity.getContentResolver();
Uri newUri = resolver.insert(Notepad.Notes.CONTENT_URI, values);
Note: values is an instance of the ContentValues class
Find media titles and albums
Using the Android provided Media Store Content Provider
String[] projection = { MediaStore.Audio.AudioColumns.ALBUM,
MediaStore.Audio.AudioColumns.TITLE };
Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
Cursor cursor = getContentResolver().query(uri, projection, null, null, null);
int aX= cursor.getColumnIndexOrThrow(MediaStore.Audio.AudioColumns.ALBUM);
int tX = cursor.getColumnIndexOrThrow(MediaStore.Audio.AudioColumns.TITLE);
IllegalArgumentException
String[] result = new String[cursor.getCount()];
while (cursor.moveToNext())
{ String title = cursor.getString(tX), album = cursor.getString(aX);
result[cursor.getPosition()] = title + " (" + album + ")";
}
cursor.close();
Other Native Content Providers: Browser, Contacts, Calendar, Call log
Accessing the Contact List
int iDCol = ContactsContract.Contacts.ID;
int nameCol = ContactsContract.Contacts.DISPLAY_NAME;
Uri uri = ContactsContract.Contacts.CONTENT_URI;
String[] projection = { iDCol, nameCol };
Cursor cursor = getContentResolver().query(uri, projection, null, null, null);
int nameIndex = cursor.getColumnIndexOrThrow(nameCol);
int idIndex = cursor.getColumnIndexOrThrow(contactIDCol);
String[] result = new String[cursor.getCount()];
while(cursor.moveToNext())
{ String name = cursor.getString(nameIndex);
String id = cursor.getString(idIndex);
result[cursor.getPosition()] = name + " (" + id + ")";
}
cursor.close();
Searchable Applications
• Expose the application to search-facilities
• Alternatives
– Search bar appearing after hardware search button
pressed or a program method call
– Search widget placed somewhere on the application
view
– Quick Search implemented as a home screen widget
– Enable voice search
Making an Application Searchable
• In the manifest
– Create an xml file with the searchable attributes
– Mark the application searchable
– Define the intent for the activity processing searches
• Either create a search activity (or SearchFragment)
– Launch when the search is initiated
– Process and display the results
• Or use a search dialog (floating search box)
– Hidden by default, but can be initiated by calling
onSearchRequested(), which is an Activity class method
– If the device doesn’t contain a dedicated search button, add a menu
option or widget that calls onSearchRequested()
• Or use the SearchView widget
Searchable configuration in res/xml
Filename: searchable.xml
<?xml version="1.0" encoding="utf-8"?>
<searchable
xmlns:android=http://schemas.android.com/apk/res/android
android:label="@string/app_label"
android:hint="@string/search_hint" >
</searchable>
• The label (required attribute) becomes visible when search is
launched and contains the search application name
• The hint appears in the search box before users enter a query. It
contains a hint about what can be searched
• Other attributes are for search suggestions and voice search
Searchable launch in Manifest
<application> …
<activity android:name=".SearchActivity“
android:launchMode="singleTop">
<intent-filter>
<action android:name="android.intent.action.SEARCH" />
</intent-filter>
<meta-data android:name="android.app.searchable"
android:resource="@xml/searchable"
/>
</activity>
Note: singleTop prevents multiple instances on the back stack
Note: launched when search is activated
Search Activity
@Override
public void onCreate(Bundle savedInstanceState)
{ super.onCreate(savedInstanceState);
setContentView(R.layout.search);
// Get the intent, verify the action and get the query
Intent intent = getIntent();
if (Intent.ACTION_SEARCH.equals(intent.getAction()))
{ String query = intent.getStringExtra(SearchManager.QUERY);
doMySearch(query); // Process the request
}
}
Services
User selects item to
download
• Services handle background events
onButtonClick() method
separate from a View
gets control in the
• Services reside in the main thread
executing activity
of the launching process! Use
thread facilities to avoid blocking
Main Activity
the main thread
• Only foreground activities have a Activity uses an intent to request the download
higher priority, so services are
from the Service!)
rarely terminated by the OS
• Proper Handling
Service
– Main activity requests services
– Service starts worker threads toStart new worker thread Done downloading!
perform requests
– Bind services to the main
New worker
Worker Thread
thread
thread
(downloading)
– Callbacks to the main activity
Downloading Threads (maybe thread pool?)
completes transactions.
Creating a Service
1. Create a class extending the service class
2. Register the service in the application manifest
<service android:enabled="true"
android:name=".MyService"
android:permission="foo.bar.MY_SERVICE_PERMISSION"/>
4. Start and stop of the service in the main activity
5. Use separate threads for compute-bound operations
Binding the service to the main activity enables the main
activity to call service class methods and then update its user
interface views
6. Self-terminate the service when it is no longer needed
Note: the permission an entity must have for the launch to succeed
Starting and Stopping Services
• Explicitly start My Service
Intent intent = new Intent(this, MyService.class);
startService(intent); }
• Implicitly start a music Service
Intent intent = new Intent(MyMusicService.PLAY_ALBUM);
intent.putExtra(MyMusicService.ALBUM_NAME_EXTRA, "United");
intent.putExtra(MyMusicService.ARTIST_NAME_EXTRA, "Pheonix");
startService(intent);
• Explicitly stop My Service :
stopService(new Intent(this, MyService.class));
• Implicitly stop Music Service
stopService(new Intent(MyMusicService.PLAY_ALBUM));
Creating a Bindable Service
Purpose: Enable activities to access service methods
public class LocalService extends Service
{ private final IBinder binder = new LocalBinder();
public class LocalBinder extends Binder // Binder implements IBinder
{ LocalService getService() { return LocalService.this; } }
@Override public void onCreate()
{ // TODO: Actions to perform when service is created. }
// Return instance after activity call onBindService() call
@Override public IBinder onBind(Intent intent)
{ return binder; }
/* method for clients */
public int getRandomNumber() { return Math.random(); }
}
public class BindingActivity extends Activity
{ LocalService service;
// An Activity using a Bound Service
private ServiceConnection connection = new ServiceConnection() // Anonymous instance
{ @Override public void onServiceConnected(ComponentName name, IBinder binder)
{ service=((LocalBinder)binder).getService(); }
@Override public void onServiceDisconnected(ComponentName arg0)
{ service = null; }
};
@Override protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main); }
@Override protected void onStart()
{ super.onStart();
bindService(new Intent(LocalService.class), connection, Context.BIND_AUTO_CREATE);
}
@Override protected void onStop()
` { super.onStop(); if (service != null) { unbindService(connection); service = null; } }
public void onButtonClick(View v)
{ if (service!=null) { int num = service.getRandomNumber();
Toast.makeText(this, "number: "+num, Toast.LENGTH_SHORT).show(); } }
}
Updating the GUI from a Thread
1. The activity registers a listening object
2. Use a Handler in an activity to process queue of runnables
private final Handler handler = new Handler();
private OnClickListener buttonListener = new OnClickListener()
{ public void onClick(View v)
{ new Thread(new Runnable()
{ pubic void run()
{ //.... hard work in separate thread
handler.post(new Runnable() { public void run() { // ... update the UI } });
}).start();
}
};
}
Note: There are other possibilities. For example, one
could use AsyncTask