Application Fundamentals | Android Developers
- An intent is an Intent
object that holds the content of the message. For activities and services,
it names the action being requested and specifies the URI of the data to
act on, among other things. For example, it might convey a request for
an activity to present an image to the user or let the user edit some
text. For broadcast receivers, the Intent object names the action being
announced. For example, it might announce to interested parties that the
camera button has been pressed. - All the activities in a task move together as a unit. The entire task (the entire
activity stack) can be brought to the foreground or sent to the background.
Suppose, for instance, that the current task has four activities in its stack
— three under the current activity. The user presses the HOME key, goes
to the application launcher, and selects a new application (actually, a new task).
The current task goes into the background and the root activity for the new task is displayed.
Then, after a short period, the user goes back to the home screen and again selects
the previous application (the previous task). That task, with all four
activities in the stack, comes forward. When the user presses the BACK
key, the screen does not display the activity the user just left (the root
activity of the previous task). Rather, the activity on the top of the stack
is removed and the previous activity in the same task is displayed. - The stack contains objects, so if a task has more than one instance of the same
Activity subclass open — multiple map viewers, for example — the
stack has a separate entry for each instance. Activities in the stack are never
rearranged, only pushed and popped. - Simply put, a task is what the user
experiences as an "application."
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