Android
- Activities. An activity represents a single screen
with a user interface just like window or frame of Java. Android activity is the subclass of
ContextThemeWrapper class. The Activity
class defines the following call backs i.e. events. Learn Android from
certified experts by Learn IT Training see
Android training for details.
The
concept of Activities
The activity class serves as the entry point
for an app’s interaction with the user, providing the window in which
the app draws its UI. This window typically fills the screen, but may be
smaller than the screen and float on top of other windows. You implement an
activity as a subclass of the Activity class. Generally, one activity implements
one screen in an app. For instance, one of an app’s activities may implement
the Preferences screen, while another activity
implements the Compose
Email screen.
Most apps contain multiple screens, which means they
comprise multiple activities. Typically, one activity in an app is specified as
the main
activity, which is the first screen to appear when the user
launches the app. Each activity can then start another activity in order to
perform different actions. For example, the main activity in a simple e-mail
app may provide the screen that shows an e-mail inbox. From there, the main
activity might launch other activities that provide screens for tasks like
writing e-mails and opening individual e-mails.
Although activities work together to form a cohesive user
experience in an app, each activity is only loosely bound to the other
activities; there are usually minimal dependencies among the activities in an
app. In fact, activities often start up activities belonging to other apps. For
example, a browser app might launch the Share activity of a social-media app.
To use activities in your app, you must register information
about them in the app’s manifest, and you must manage activity lifecycles
appropriately. The rest of this document introduces these subjects.
If you have worked with C, C++ or Java programming language (JAVA training by experts makes you to
become professional in programming) then you must have seen that your program
starts from main() function.
Very similar way, Android system initiates its program within an Activity starting with a call on onCreate()
callback method. There is a sequence of callback methods that start up an
activity and a sequence of callback methods that tear down an activity as shown
in the Activity life cycle diagram.
The Activity class defines the following call backs i.e.
events. You don't need to implement all the callbacks methods. However, it's
important that you understand each one and implement those that ensure your app
behaves the way users expect.
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