Android - Activity, Services
- 1. Mobile Application Development Activity & Services
- 2. Android User Interfaces 1. Activities 2. Layouts 3. Menus 4. Dialogs 5. Intents 6. Notifications
- 3. Creating an Activity • Create a new Activity by extending the Activity class. • Override the onCreate() method to set the view for the activity • Set the user interface to an Activity using the setContentView() method in the onCreate method of the Activity. public class MyActivity extends Activity { public void onCreate(Bundle b) { super.onCreate(b); setContentView(R.layout.main); } }
- 4. • Activities in the system are managed as an activity stack. • The Android memory manager uses this stack to determine the priority of applications based on their Activities when deciding which application to terminate to free resources. • An activity has essentially four states: Active : An activity in the foreground of the screen. Paused : An activity has lost focus but is still visible. Stopped : An activity is completely obscured by another activity. Inactive : After an Activity has been killed or before it has been launched. Activity Life Cycle
- 6. Activity Lifetimes • Entire lifetime : Happens between the first call to onCreate(Bundle) through to a single final call to onDestroy(). An activity will do all setup of "global" state in onCreate(), and release all remaining resources in onDestroy(). • Visible lifetime : Happens between a call to onStart() until a corresponding call to onStop(). During this time the user can see the activity on- screen, though it may not be in the foreground and interacting with the user. • Foreground lifetime : Happens between a call to onResume() until a corresponding call to onPause().
- 7. Layouts • Layout is the design plan or the architecture for the user interface in an activity. • Layout is required to arrange or organize the widgets inside an activity. • Layout defines the activity structure & holds all the elements that are part of the user interface. • Layouts can be nested.
- 8. A Layout can be declared in two ways: • Declaring in XML: Android provides a straightforward XML tags that corresponds to the View classes and subclasses, such as those for widgets and layouts that can be added to the layout. • Instantiating at runtime: Your application can create View and ViewGroup objects (and manipulate their properties) programmatically. Declaring Layout
- 9. • Linear Layout A layout that organizes its children into a single horizontal or vertical row. • Table Layout A layout that positions its children into rows and columns. • Relative Layout A layout that allows to organize child elements in positions relative to the parent or siblings elements. • Frame Layout It is designed to block out an area on the screen to display a single item. Layout Types
- 11. Menus • Menus provide familiar interfaces to expose application functions without sacrificing screen space. • Android offers an easy programming interface to provide standardized application menus. • Android offers three fundamental types of application menus: Options Menu Context Menu Sub-menu
- 12. • By default, every Activity supports an Options menu. It is revealed by pressing the device MENU key. • Options Menu has two groups of menu items: Icon Menu Collection of maximum of six menu items Supports Icons and short-cuts Expanded Menu Exposed by the 'More' menu item Displayed when the icon menu becomes over-loaded Comprised of sixth options menu item and the rest. Options Menu
- 13. Options Menu
- 14. Context Menu • Context menu is a floating menu that is associated with a control. • Context menu is launched when the control has the focus and the D pad is pressed. • Context menus can be assigned to any View within an Activity. • It provides functions relating to the view, to which it is registered. • It supports submenus, checkboxes, radio buttons. • It does not support shortcuts and icons.
- 15. Context Menu
- 16. • Sub menu is a floating menu, it can be a child menu of options menu or context menu. • It supports checkboxes, radio buttons and shortcut keys. • It does not support item icons, or nested sub menus. Sub Menu
- 17. Sub Menu
- 18. • A dialog is a small window that appears in front of an Activity. • The underlying Activity loses focus and the dialog accepts all user interaction. • Normally used for notifications and short activities that directly relate to the application in progress. • Android supports following types of dialogs. Alert Dialog Progress Dialog Date Picker Dialog Time Picker Dialog Toast Dialog
- 19. • A dialog that can manage zero, one, two or three buttons. • It can also manage a list of selectable items that can include checkboxes or radio buttons. • The AlertDialog is capable of constructing most dialog user interfaces and is the suggested dialog type. • AlertDialog class is a subclass of Dialog class and has a nested subclass AlertDialog.Builder to construct a dialog. Alert Dialog
- 21. Other Dialogs • Progress Dialog A dialog that displays a progress wheel or progress bar. It supports buttons like in AlertDialog. • DatePicker Dialog A dialog that allows the user to select a date. • TimePicker Dialog A dialog that allows the user to select a time.
- 23. • A toast is a transient Dialog box containing a quick little message for the user. • Toasts never receive focus and they don’t interrupt the active application. • They provide an ideal mechanism for alerting users to events occurring in background Services without interrupting foreground applications. Toast
- 24. • Intents are the messages that are used to activate following application components: Activities Services Broadcast Receivers • Intent is an object, which has a data structure holding any one of the following data : Abstract description of an operation to be performed In the case of broadcasts, a description of something that has happened and is being announced. Intents
- 25. Application components are invoked through intents in the following way : • Activity : Intent object is passed to following functions to invoke the Activity. Context.startActivity (Intent intent) Activity.startActivityForResult (Intent intent, int requestCode) • Service : Intent object is passed to following functions to invoke the Service. Context.startService (Intent) Context.bindService (Intent) Invoking Components
- 26. • Broadcast Receivers : Intent object is passed to following functions to invoke the Broadcast Receiver. Context.sendBroadcast ( Intent intent, String receiverPermission) Context.sendOrderedBroadcast ( Intent intent, String receiverPermission) Context.sendStickyBroadcast ( Intent intent ) Invoking Components
- 27. • A status bar notification adds an icon to the system's status bar (with an optional ticker-text message) and an expanded message in the "Notifications" window. • When the user selects the expanded message, Android fires an Intent that is defined by the notification (usually to launch an Activity). • You can also configure the notification to alert the user with a sound, a vibration, and flashing lights on the device. • This kind of notification is ideal when your application is working in a background Service and needs to notify the user about an event. Notification
- 28. • To create a notification, following classes should be used: Notification NotificationManager • Notification is a class that represents how a persistent notification is to be presented to the user using the NotificationManager. • NotificationManager is an Android system service used to handle notifications. Notification (Continued)
- 31. • A Service is an application component that runs in the background for an indefinite period of time. • Services are specifically used to handle operations and functionality that should run silently, without any User Interface. • Services are generally used to perform following operations in the background Updating the Content Providers Firing Intents Triggering Notifications etc • Services, like other application objects, run in the main thread of their hosting process. Services
- 32. • Services are started, stopped, and controlled from other application components including other Services, Activities, and Broadcast Receivers. • Service is involved in any CPU intensive (such as MP3 playback) or blocking (such as networking) operations, should spawn its own thread to do that work. • Android platform has following services: Location Manager Media Controller Notification Manager Services (Continued)
- 33. • Service supports following lifecycle methods : OnCreate OnStart OnBind OnUnbind OnRebind OnDestroy • Service is controlled using following methods: Context.startService Context.stopService Service.stopSelf Context.bindService Context.UnbindService Service Life Cycle
- 35. 1. Professional Android Application Development, Reto Meier, Wrox, November 2008 2. Beginning Android, Mark Murphy, Apress, June 2009 3. Pro Android, Sayed Y Hashimi, Apress, June 2009 4. Android – Application Development, Rick Rogers et.al, O’Reilly, May 2009 5. “Hello, Android”, Introducing Google’s Mobile Development Platform, Ed Burnette, The Pragmatic Bookshelf, 2008 6. developer.android.com References