Daily#6. Understanding and Using NetworkCallback in Android

The NetworkCallback class plays a crucial role in handling network changes in Android. It allows apps to monitor the network's state and perform actions accordingly. It has different types such as DefaultNetworkCallback, Request type NetworkCallback and Listen type NetworkCallback.

Default Network

 In Android, the "default network" refers to the network that is currently being used for internet traffic. Most of the time, it is the network that your device is connected to for accessing the internet, either via Wi-Fi or mobile data.

 The default network can change based on factors like network availability, signal strength, and user preferences. For instance, if you're connected to both Wi-Fi and mobile data, Android generally defaults to using Wi-Fi because it's typically faster and doesn't incur data charges. However, if the Wi-Fi signal becomes weak or disconnects, Android will automatically switch the default network to mobile data (if available) to maintain internet connectivity.

 So, when we talk about a "DefaultNetworkCallback" in Android, we are referring to a callback method that will be invoked when the device's default network changes, such as when the device connects to or disconnects from a network. This allows your app to respond to changes in the device's internet connectivity, providing opportunities for improving user experience and app performance.

 DefaultNetworkCallback is a convenience callback that apps can use to handle the availability of the default network:

final ConnectivityManager.NetworkCallback networkCallback = new ConnectivityManager.NetworkCallback() {
    @Override
    public void onAvailable(Network network) {
        // Handle the availability of the default network
    }

    @Override
    public void onLost(Network network) {
        // Handle the loss of the default network
    }
};

connectivityManager.registerDefaultNetworkCallback(networkCallback);

Listen vs Request NetworkCallback

When it comes to network requests, Android's ConnectivityManager offers two types of NetworkCallback: Request type and Listen type.

Here's a more detailed comparison:

Request type NetworkCallback:

When you call requestNetwork(), Android tries to satisfy your NetworkRequest. It essentially means "I need a network with these capabilities". Android will then attempt to switch to or bring up a network that meets the request, if one is not already available.

This method should be used when your app cannot accomplish its task without a network that has the capabilities defined by the NetworkRequest.

In simpler terms, a Request type NetworkCallback is an active request, Android will take action to satisfy your request.

 

NetworkRequest request = new NetworkRequest.Builder()
    .addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
    .build();

connectivityManager.requestNetwork(request, networkCallback);

Listen type NetworkCallback:

When you call registerNetworkCallback(), you're saying "Let me know when a network of this nature comes up". However, unlike requestNetwork(), this method does not cause any sort of network switchover or any attempt to satisfy the NetworkRequest.

Use this method when your app can alternatively use whichever network is available or when you just want to know when a network of interest is available.

NetworkRequest request = new NetworkRequest.Builder()
    .addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
    .build();

connectivityManager.registerNetworkCallback(request, networkCallback);

Please, refer to Daily#2 for implementing NetworkCallback. 

 In summary, the key difference between the two is that requestNetwork() is an active request where Android will try to satisfy your network needs, while registerNetworkCallback() is more of a passive listener and won't cause Android to take any action other than notifying you of network changes.

Remember: To use these APIs, you need to add the ACCESS_NETWORK_STATE and CHANGE_NETWORK_STATE permissions to your manifest:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />