A broadcast receiver is a component which allows us to register for system or application events. All registered receivers for an event will be notified by Android once this event happens.
Android system periodically broadcast messages about things that are happening, such as the battery status changed, the Wi-Fi came on, or the phone’s orientation changed. You can pick up these state changes and perform actions after intercepting them and all this is done using broadcast receivers. Broadcast receivers receive and react to broadcasts generated by system or apps .
The below sample code depicts a broadcast receiver that call LockerActivity.class when “android.intent.action.SCREEN_OFF” is intercepted.
BroadcastReceiver broadcastReceiver=new BroadcastReceiver() {
//This method is called when the BroadcastReceiver is receiving an Intent broadcast
@Override
public void onReceive(Context context, Intent paramIntent) {
String str=paramIntent.getAction();//Retrieve the general action to be performed
//screen is OFF
if ((!"android.intent.action.SCREEN_ON".equals(str)) || ("android.intent.action.SCREEN_OFF".equals(str)))
{
Intent localIntent1 = new Intent(context, LockerActivity.class);//locker class called
//If set, this activity will become the start of a new task on this history stack.
context.startActivity(localIntent1);//starting activity
}
}
};
// Register a BroadcastReceiver to be run in the main activity thread. The receiver will be //called with any broadcast Intent that matches filter, in the main application thread.
registerReceiver(broadcastReceiver,intentfilter);
BroadcastRecievers do not have a UI but they start activities based on broadcast announcements.
Androidexterous 