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Next up, lets see how to register a Broadcast Receiver in code, so that it only receives messages while our app is currently running.
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Now we're going to change this broadcast
receiver to only work when our
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activity is running.
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Let's start by commenting
out our manifest receiver.
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We can select it all, and
hit command plus forward slash.
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Or control plus forward slash on Windows.
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Now we can work in main activity.
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So let's open that back up.
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And we'll start by adding a field for
our receiver.
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So up at the top let's add a new private
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NetworkConnectionReceiver and
let's call it mReceiver and
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now let's set it here equals
a new NetworkConnectionReceiver.
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Okay, so think back to the activity
life cycle for a moment.
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Which events do we use to make sure that
something is only running when an activity
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is alive and visible?
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That's right, onResume and onPause.
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Let's scroll down to the bottom.
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And here we already have onStart and
onStop.
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So I'm gonna group them together and
add onResume and below that, onPause.
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All right, first things first
let's add some log messages for
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what's going on with our activity.
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Log.i(TAG, and
then App is in the foreground.
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I'm going to copy this paste for pause and
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say App is in the background and
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now we want to register in on resume and
unregister in on pause.
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First thing we need to do to register is
to declare our intent filter in code.
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We're just building the same
thing we had in the manifest.
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So here in on resume, let's say,
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IntentFilter, let's name it filter
equals a new intent filter.
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And we'll use the same value
we had in the manifest,
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android.net.com.CONNECTIVITY_CHANGE.
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And now we can hook up our receiver and
filter with registerReceiver.
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We'll pass in mReceiver that we just
set up top and this new filter.
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We need to register in unpause with
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unregister receiver and
it's that same mReceiver.
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All right and now we can test this out.
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Okay let's get into the notification
drawer and if we go back to log it, we can
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scroll up a little bit and we see that
our app is currently in the foreground.
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So let's turn on airplane mode again and
then let's go back to lock it.
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And here is our connectivity change again,
cool.
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Now let's test it in the background.
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So go back to our app and
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we'll back out of it and here in logcat we
see that the app is now in the background.
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And now if we turn off airplane mode
in this case we don't get a message for
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the connectivity change.
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Our receiver is no longer operating.
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So which method should you normally
use to register a receiver,
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in the manifest or in code.
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Well it depends on what you are monitoring
for and when you need to act on it.
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Usually you only want to listen when your
activity or your service is running.
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In which case,
you'll register in code like this.
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But occasionally,
you may want to monitor for
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things whenever they occur,
even if your app isn't running.
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In those cases,
you'll need to register in the manifest.
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