However, there are ways for an application to share data with other applications and for an application to access system services:
- It's possible to arrange for two applications to share the same Linux user ID, in which case they are able to access each other's files. To conserve system resources, applications with the same user ID can also arrange to run in the same Linux process and share the same VM (the applications must also be signed with the same certificate).
- An application can request permission to access device data such as the user's contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and more. All application permissions must be granted by the user at install time.
There are separate methods for activating each type of component:
- You can start an activity (or give it something new to do) by passing an
IntenttostartActivity()orstartActivityForResult()(when you want the activity to return a result). - You can start a service (or give new instructions to an ongoing service) by passing an
IntenttostartService(). Or you can bind to the service by passing anIntenttobindService(). - You can initiate a broadcast by passing an
Intentto methods likesendBroadcast(),sendOrderedBroadcast(), orsendStickyBroadcast(). - You can perform a query to a content provider by calling
query()on aContentResolver.
Activities, services, and content providers that you include in your source but do not declare in the manifest are not visible to the system and, consequently, can never run. However, broadcast receivers can be either declared in the manifest or created dynamically in code (asBroadcastReceiver objects) and registered with the system by calling registerReceiver().
