Daily#12: Networking in Android - Understanding ConnectivityManager and Network APIs

Hello everyone! Today, let's delve into Android's networking capabilities. We'll concentrate on the ConnectivityManager class and the Network API, both of which provide applications the means to specify a network interface for communication with external networks.

ConnectivityManager and bindProcessToNetwork

Let's start with ConnectivityManager, a class that provides network connectivity status and updates applications when this connectivity changes. One crucial method in this class is bindProcessToNetwork.

ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
Network network = ... // Your desired network
cm.bindProcessToNetwork(network);

Using bindProcessToNetwork, an application can dedicate a Network object for its network traffic. Therefore, all traffic from the application will be routed over this specified network.

Acquiring a Network Object

You may be wondering how to get a Network object to use with bindProcessToNetwork. There are several ways to do so:

1. NetworkCallback (refer : previous post)

ConnectivityManager.NetworkCallback networkCallback = new ConnectivityManager.NetworkCallback() {
   @Override
   public void onAvailable(Network network) {
      // Use network object here
   }
};

2. getActiveNetwork

Network activeNetwork = cm.getActiveNetwork();

With a Network object at hand, we can utilize the Network class's methods to control network traffic.

Network and its methods: bindSocket, getSocketFactory, openConnection

The Network class represents a network interface. It has several key methods:

1. bindSocket(Socket socket): Binds the specified Socket to this Network, ensuring that all data traffic from the Socket will be sent over this Network.

Network network = ... // Your Network
Socket socket = new Socket();
network.bindSocket(socket);
OutputStream os = socket.getOutputStream();
os.write("Hello, world!".getBytes());
os.close();
socket.close();

2. getSocketFactory(): Returns a SocketFactory that creates Sockets bound to this Network.

SocketFactory sf = network.getSocketFactory();
Socket socket = sf.createSocket("example.com", 80);
OutputStream os = socket.getOutputStream();
os.write("Hello, world!".getBytes());
os.close();
socket.close();

3. openConnection(URL url): Opens a URLConnection over this network. It can be used to create an InputStream or OutputStream.

URL url = new URL("http://example.com");
URLConnection connection = network.openConnection(url);
InputStream is = connection.getInputStream();
// Use InputStream here
is.close();

By utilizing these methods, an application can explicitly send network traffic over a particular network interface, ensuring that data is routed correctly.

Remember, this is just a brief dive into Android's vast networking capabilities. There are many more classes and methods to explore. As always, refer to the official Android documentation for more details and don't stop experimenting!