Pro Android with Kotlin

18
CHAPTER 3: Activities
When the called intent returns the way described earlier, the calling component needs to be 
informed of that event. This is done asynchronously since the 
startActivityForResult()
method immediately returns and does not wait for the called activity to finish. The way this event 
gets caught nevertheless is by overriding the 
onActivityResult()
method, as shown here:
override
fun onActivityResult(requestCode:Int, resultCode:Int,
data:Intent) {
// do something with 'requestCode' and 'resultCode'
// returned data is inside 'data'
}
requestCode
is whatever you set inside 
startActivityForResult()
as 
requestCode
, and 
resultCode
is what you wrote as the first argument in 
setResult()
in the called activity.
Caution
On some devices, 
requestCode
has its most significant bit set to 1, no matter 
what was set before. To be on the safe side, you can use the Kotlin construct inside 
onActivityResult()
as follows:
val requestCodeFixed = requestCode and 0xFFFF
Intent Filters
Intents are objects to tell Android that something needs to be done, and they can be 
explicit
by exactly specifying which component needs to be called or 
implicit
if we don’t specify the 
called component but let Android decide which app and which component can answer the 
request. In case there is some ambiguity and Android cannot decide which component to 
call for implicit intents, Android will ask the user.
For implicit intents to work, a possible intent receiver needs to declare which intents it is able 
to receive. For example, an activity might be able to show the contents of a text file, and a 
caller saying “I need an activity that can show me text files” possibly connects to exactly this 
activity. Now the way the intent receiver declares its ability to answer intent requests is by 
specifying one or more 
intent filters
in its app’s 
AndroidManifest.xml
file. The syntax of such 
a declaration is as follows:
android:label="string resource"
android:priority="integer" >
...

Here, 
icon
points to a drawable resource ID for an icon, and 
label
points to a string 
resource ID for a label. If unspecified, the icon or label from the parent element will be used. 
The 
priority
attribute is a number between -999 and 999 and for intents specifies its ability 
to handle such intent request, and for receivers specifies the execution order for several 
receivers. Higher priorities come before lower priorities.

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