Java 7 Meets Android - Beginning Java 7 - page 1158

Incontrast, onDestroy() isusuallyimplementedtofreeenvironmentalresources
(e.g., threads) that are associated with an activity so that a destroyed activity doesn't
leave such things around while the rest of its app is still running.
Figure12-3 revealsthatanactivityisstartedbycalling startActivity() .More
specifically,theactivityisstartedbycreatingan Intent objectdescribinganexplicit
or implicit intent, and by passing this object to Context 's void startActiv-
ity(Intent intent) method(launchanewactivity;noresultisreturnedwhenit
finishes).
Alternatively, the activity could be started by calling Activity 's void
startActivityForResult(Intent intent, int requestCode) meth-
od. The specified int result is returned to Activity 's void onActivityRes-
ult(int requestCode, int resultCode, Intent data) callbackmeth-
od as an argument.

Note The responding activity can look at the initial intent that caused it to be
launched by calling Activity 's Intent getIntent() method. Android calls
theactivity's void onNewIntent(Intent intent) method(alsolocatedinthe
Activity class) to pass any subsequent intents to the activity.

Listing 12-1 ' s package statement implies an app named SimpleApp . As well as
SimpleActivity serving as its main activity, let's assume that this app includes a
SimpleActivity2 class describing an activity for viewing JPEG images. Suppose
that you want to start SimpleActivity2 from SimpleActivity 's
onCreate(Bundle) method.Thefollowingexampleshowsyouhowtoaccomplish
this task:
Intent intent = new Intent(SimpleActivity.this, Sim-
pleActivity2.class);
SimpleActivity.this.startActivity(intent);
Thefirstlinecreatesan Intent objectthatdescribesanexplicitintent.Itinitializes
this object by passing the current SimpleActivity instance's reference and Sim-
pleActivity2 's java.lang.Class instancetothe Intent(Context pack-
ageContext, Class<?> clazz) constructor.
Thesecondlinepassesthis Intent objectto startActivity(Intent) ,which
is responsible for starting the activity described by SimpleActivity2.class .
If startActivity(Intent) was unable to find the specified activity (which
shouldn't

happen), it would throw an

an-

droid.content.ActivityNotFoundException instance.