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Page References

Incoming links Outgoing links
Coursera-android...nobody
Coursera-android

Version management

Difference between version and

At line 24 changed 3 lines
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.. not many notes on this subject , no time and interest this time....
__MultiMedia__
Important MultiMedia classes:
* AudioManager & SoundPool
* RingtoneManager & RingTone
* MediaPlayer & MediaRecorder
* Camera
__AudioManager__
* manages volume, system sound, effects and ringer mode control
* acquire AudioManager instance via Context.getSystemService(Context.AUDIO_SERVICE)
* then Load and Play sound Effects, manage the volume, manage Peripherals
__SoundPool__ represents a collection of audio, multiple sample at the same time
__RingToneManager__ provides access to audio clips used for incoming phone calls, notifications, alarms etc.
It allows application to get and set ringtones and to stop/play them.
__MediaPlayer__ controls the playback of audio and video streams and files.
common methods
* setDataSource() - which streams to play
* prepare() - initializes the player and loads the streams (it is synchronous, there is also an asynchronous version)
* start()
* pause()
* seekTo()
* stop()
* release()
__VideoView__ is a subclass of SurfaceView. Used for displaying video.
__MediaRecorder__ used to record audio and video (state machine). Use ''setAudioSource()'' , ''setVideoSource()'', and the other usual ones.
__Camera__ - access the camera service. Your application can capture images, start/stop preview. You need CAMERA permissions of course. Also specify the ''uses-feature'' tag in AndroidManifest.xml.
Commona approach:
* get camera instance
* set camera parameters
* setup and start the preview display (so the user can see what the camera sees)
* take a picture & process image data
* release the camera
! week 7
__Sensors__
Sensors are hardware devices that measure the physical environment.
There are 3 type of sensors:
* Motion (speed and acceleration)
* Position (magnetic compass)
* Environment (pressure, ambient light)
Important classes:
* SensorManager (''getSystemService(Context.SENSOR_SERVICE)''), to access a specific sensor : ''SensorManager.getDefaultSensor(int type)'' :
** Sensor.TYPE_ACCELEROMETER
** Sensor.TYPE_MAGNETIC_FIELD
** Sensor.TYPE_PRESSURE
* SensorEventListener interface must be implemented to get callbacks when there are new sensor readings or when a sensor's accuracy changes. (''onAccuracyChanged(Sensor sensor, int accuracy)'' or ''onSensorChanged(SensorEvent event)'' ) also make sure to call ''un/registerSensor()''
For registration you also pass in the rate at which you want your callbacks.
For unregistration you pass in the listener and a bitmask that specifies the Sensors to release.
* SensorEvent
** data is sensor-specific
** sensor type
** timestamp
** accuracy
** measurement data
__Sensor Coordinate System__
This does not change if the orientation changes.
* X - right to left
* Y - top to bottom
* Z - down to up
Sensor values will vary constantly, for example, you cannot hold your device exactly straight or steady.
So these values can be filtered, in multiple ways:
* Low-pass filter
** deemphasize small transient force changes
** emphasize long term constant forces
** for example : een waterpas
* high -pass filter
** should ignore long term changes
** emphasize short term changes
** for example : a percussion instrument
__Location & maps__
Classes :
* Location
** represent position on the earth
** has : latitude, longitude, timestamp
** optionally : accuracy, altitude, speed, bearing
* LocationProvider
** represents a location data source, actual data may come from Satellites, Cell phone towers, Wifi APs
** LocationProvider types:
*** network (wifi and cell tower) ==> permission ACCESS_COARSE_LOCATION
*** GPS - satellite ==> permission ACCESS_FINE_LOCATION
*** passive - piggyback on the readings requested by other applications ==> permission ACCESS_FINE_LOCATION
Different __Tradeoffs__ for each provider between:
* cost
* accuracy
* availability
* timeliness
* GPS - expensive, accurate, slower, available outdoors
* Network - cheaper, less accurate, faster, but wifi or cell phone tower required
* passive - cheapest, fastest, not always available
LocationManager options:
* determine last know location
* register for location updates (LocationListener interface)
* register to receive intents when device nears or moves away from given geographic area
Procedure for getting location:
* start listening for location updates
* maintain a "current best estimate" of location
* determine when good enough, en then unregister the listener
* use best estimate
__MAPS__
A visual presentation of area.
Android provides maps support through the Google Maps Android V2 API
Map types:
* normal maps (tradition road map)
* satellite maps (aerial photograph)
* hybrid maps (both combined)
* terrain maps (topographic details)
Customizing the map:
* change the camera position (zoom)
* add markers and ground overlays
* respond to gestures (pinch and zoom)
* indicate current location
Some map classes:
* GoogleMap
* MapFragment
* Camera
* Marker
Setting up Maps application:
* set up the google play services SDK
* obtain an API key
* specify settings in AndroidManifest.xml
* add map to project
Required permissions:
* INTERNET (to get the maps from google)
* ACCESS_NETWORK_STATE (to determine if maps can be downloaded)
* WRITE_EXTERNAL_STORAGE (to save map data)
* com.google.android.providers.gsf.permission.READ_GSERVICES
* one or more LOCATION perms
! week 8
__Data management__
__SharedPreferences__\\
Small amounts of primitive data.\\
A persistent map, key-values, are persisted across application sessions.
''Activity.getPreferences(mode)'' (mode=private) for one activity.\\
''Context.getSharedPreferences(name, mode)'' for data shared across multiple activities.
SharedPreferences.edit() returns a SharedPreferences.Editor object, and then things like ''putInt() putString() and remove(key)'', and finally ''Editor.commit()''.
retrieving sharedprefs:
* getAll()
* getString()
* getBoolean()
__PreferenceFragment__\\
To display and modify User Preferences.
__File Storage__
__Internal Storage__\\
Small to medium amounts of private data, private to the applications.
__File API__
''FileOutputStream.openFileOutput(String name, int mode) '' opens private file for writing, creates it if it does not exist.
__External Storage__\\
Larger amounts of data that is non-private, such as media files.
Media can appear and disappear without warning. So first determine the state of the storage, with ''Environment.getExternalStorageState()''.
* MEDIA_MOUNTED - read/write access
* MEDIA_MOUNTED_READ_ONLY
* MEDIA_REMOVED
Requires permission: __WRITE_EXTERNAL_STORAGE__
__Cache files__
* removed when storage is low
* removed when app is uninstalled
''Context.getCacheDir()'' returns absolute path to directory for temporary files.
''Context.getExternalCacheDir()''
__Databases__\\
Small to medium amounts of structured private data.
__SQLite__ is full fledged, implements most of SQL92 and supports ACID transactions (Atomic, Consistent, Isolated, Durable).\\
* Create subclass '' SQLiteOpenHelper''. Call super() from subclass constructor to init the db.
* override the onCreate() and onUpgrade()
* use open and return methods
Database are stored in ''/data/data/<packagename>/databases'' directory
__Content Providers__
Centralized repository of structured data to be shared by multiple applications
''ContentResolver'' class provides a db-style interface to the content provider (query , insert ,delete, update), also supports listeners (for updated information for example)
''Context.getContentResolver()'' gets ref to ContentResolver.
Example ContentProviders :
* Browser - bookmarks, history
* call log - telephone usage
* contacts - contact data
* media - media database
* userdictionary - database for predictive spelling
Data is represented as a database table.
Application identify the data they want with a __URI__ :
__content://authority/path/id__
* content is fixed for content providers
* authority - id for the content provider
* path - 0 or more segments indicating the type of data
* id - a specific record (key)
__CursorLoader__
for intensive tasks loading data, it uses an AsyncTask. using the ''Loader.initLoader()'' passing in the Loader Callbacks.
__Creating a ContentProvider__
* implement a storage subsystem (SQLite for example)
* define a contract class to support users of your contentprovider
* implement a ContentProvider subclass
* declare and config it in the AndroidManifest.xml (''provider'' tag)
__Services__
Services do not interact with users, so no user interface.
* perform background processing , even if application terminates
* allow code in one process to interact with code in another process
''Context.startService(Intent)''
Android can kill a service if it needs it's resources.
Services run in the main thread of the hosting application.
Binding to a service with ''Context.bindService(Intent, ServiceConnection, flags)'' .
A component can send requests to and receive response from a service.
A service will keep running as long as at least one component is connected.
''Messenger'' class manages a handler. It allows message to be sent from one component to another. So use it for sequential processing.
The receiving component needs a Handler to process the messages, and creates a Messenger that provides a binder to a client that binds to the service??
The client binds to a service and receives a Binder object, this binder object is used to create a Messenger, which knows how to send messages to the Handler that was set up by the service .
The client then uses the Messenger to send messages to the Handler in the service.
If you need services that are accessed in parallel , you need __AIDL__ (Android Interface Definition Language)
* define remote interface
* implement remote service
* implement service methods
* implement client methods
Create a .aidl file. Defines how components can interface with your service. It is similar to Java interfaces.
AIDL types :
* Java primitives
* String
* CharSequence
* other AIDL-generated interfaces
* classes implementing the Parcelable interface
* List with the above
* Map with the above
* > Generic maps not supported
Services must implement a inner class called <class>.Stub.
This page (revision-58) was last changed on 23-Apr-2022 17:06 by HarryMetskeTop