Difference between registerDefaultNetworkCallback and registerNetworkCallback

Question

I came across registerDefaultNetworkCallback and registerNetworkCallback while updating my Android app for API 28.

Having reviewed the documentation, I cannot find the difference between registering a network callback and registering a default network callback.

When will one use which?

Thanks in advance :)

Answer 1

As far as I understood, the difference between registerDefaultNetworkCallback and registerNetworkCallback it's only based on customisation.
registerDefaultNetworkCallback works (surprisingly) as a default network listener, while registerNetworkCallback it's more configurable. For example:

    val connectivityManager = getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager      val builder = NetworkRequest.Builder()     builder.addTransportType(NetworkCapabilities.TRANSPORT_CELLULAR)      val networkRequest = builder.build()     connectivityManager.registerNetworkCallback(networkRequest,      object : ConnectivityManager.NetworkCallback () {         override fun onAvailable(network: Network?) {             super.onAvailable(network)             Log.i("Test", "Network Available")         }          override fun onLost(network: Network?) {             super.onLost(network)             Log.i("Test", "Connection lost")         }     }) 

Here onAvailable will be called only if the user connects to a cellular network (by connecting to WiFi it won't log anything). The same does onLost when disconnecting from cellular network.

If we do it like this:

    connectivityManager.registerDefaultNetworkCallback(object  : ConnectivityManager.NetworkCallback() {         override fun onAvailable(network: Network?) {             super.onAvailable(network)             Log.i("Test", "Default -> Network Available")         }          override fun onLost(network: Network?) {             super.onLost(network)             Log.i("Test", "Default -> Connection lost")         }     }) 

Both functions work as default callbacks when the user is connecting (or disconnecting) to/from a network (it can be either WiFi or cellular).

These are just some very basic examples. Of course NetworkRequest can have a lot of configurations by setting its capability or transportType. You can read more about these in the official documentation of NetworkRequest.

Answer 2

registerNetworkCallback() was added in API level 21 (Android 5.0, Lollipop). It allows you to listen for changes in networks which satisfy a certain transport type (WiFi, cellular, Bluetooth, ...) and capability (SMS, NOT_METERED, ...).

registerDefaultNetworkCallback() was added in API level 24 (Android 7.0, Nougat) and uses your callback when any network change occurs, regardless of transport type and capability.

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Example for registerNetworkCallback(). At least in my case I do not care about the filters and want my code to run for any network type. This can be achieved with an empty Builder object:

/* Automatically start a download once an internet connection is established */ val cm = getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager // could filter using .addCapability(int) or .addTransportType(int) on Builder val networkChangeFilter = NetworkRequest.Builder().build() cm.registerNetworkCallback(networkChangeFilter,      object : ConnectivityManager.NetworkCallback() {         override fun onAvailable(network: Network) = downloadStuff()     } ) 

Above code is equivalent to this code with registerDefaultNetworkCallback():

val cm = getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager cm.registerDefaultNetworkCallback(     object : ConnectivityManager.NetworkCallback() {         override fun onAvailable(network: Network) = downloadStuff()     } ) 

The confusingly named NetworkRequest is actually just a filter for transport type and capability.

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The Default version is less code, but has a lower API level and thus supports fewer phones (74% vs 94%). Since I could not find a backwards-compatible version of this API call in ConnectivityManagerCompat I recommend using the first version if API levels 21-23 matter to you.