Pro Android with Kotlin

55
CHAPTER 5: Broadcasts

ACTION_NEW_OUTGOING_CALL:
This intercepts outgoing calls.

ACTION_DEVICE_OWNER_CHANGED:
Some apps might need to receive this so that they know the device’s 
security status has changed.

ACTION_EVENT_REMINDER:
This is sent by the calendar provider to post an event reminder to the 
calendar app.

ACTION_MEDIA_MOUNTED,
ACTION_MEDIA_CHECKING, ACTION_MEDIA_UNMOUNTED, ACTION_MEDIA_EJECT, 
ACTION_MEDIA_UNMOUNTABLE,ACTION_MEDIA_REMOVED, ACTION_MEDIA_BAD_
REMOVAL:
Apps might need to know about the user’s physical interactions with the 
device.

SMS_RECEIVED_ACTION, WAP_PUSH_RECEIVED_ACTION:
These are needed by SMS recipient apps.
Adding Security to Broadcasts
Security in broadcasting messages is handled by the permission system, which gets 
handled in more detail in Chapter 
7
.
In the following sections, we distinguish between explicit and implicit broadcasts.
Securing Explicit Broadcasts
For nonlocal broadcasting (i.e., not using the LocalBroadcastManager), permissions can be 
specified on both sides, the receiver and the sender. For the latter, the broadcast-sending 
methods have overloaded versions, including a permission specifier:
...
val intent = Intent(this, MyReceiver::class.java)
...
sendBroadcast(intent, "com.xyz.theapp.PERMISSION1")
...
This expresses sending a broadcast to a receiver that is protected by com.xyz.theapp.
PERMISSION1. Of course, you should write your own package names here and use 
appropriate permission names.

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56
CHAPTER 5: Broadcasts
Instead, sending a broadcast without a permission specification may address receivers with 
and without permission protection:
...
val intent = Intent(this, MyReceiver::class.java)
...
sendBroadcast(intent)
...
This means that specifying permissions on the sender side is not supposed to tell the 
receiver that the sender is protected in any way.
For adding permissions to the receiver side, we first need to declare using it inside 
AndroidManifest.xml on an app level.

"com.xyz.theapp.PERMISSION1"/>
...
Next we explicitly add it to the receiver element inside the same manifest file.
android:permission="com.xyz.theapp.PERMISSION1">

"com.xyz.theapp.DO_STH" />


Here, MyReceiver is an implementation of android.content.BroadcastReceiver.
Third, since this is a custom permission, you have to declare itself in the manifest file.

"com.xyz.theapp.PERMISSION1"/>
...
The 
 allows for a couple of more attributes; see the section “Manifest Top Level 
Entries” in the online text companion to learn more about the protection level. The details for 
and implications of it are explained thoroughly in Chapter 
7
.
For noncustom permissions, you don’t need to use the 
 element.
Caution Specifying a permission on the sender side without having a matching permission on the 
receiver side silently fails when you try to send a broadcast. There are also no logging entries, so be 
careful with sender-side permissions.

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