Connect to the network

To perform network operations in your application, your manifest must include the following permissions:

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

Best practices for secure network communication

Before you add networking functionality to your app, you need to ensure that data and information within your app stay safe when you are transmitting over a network. To do so, follow these networking security best practices:

  • Minimize the amount of sensitive or personal user data that you transmit over the network.
  • Send all network traffic from your app over SSL.
  • Consider creating a network security configuration, which lets your app trust custom certificate authorities (CAs) or restrict the set of system CAs that it trusts for secure communication.

For more information on how to apply secure networking principles, see the networking security tips.

Choose an HTTP client

Most network-connected apps use HTTP to send and receive data. The Android platform includes the HttpsURLConnection client, which supports TLS, streaming uploads and downloads, configurable timeouts, IPv6, and connection pooling.

Third-party libraries that offer higher-level APIs for networking operations are also available. These support various convenience features, such as the serialization of request bodies and deserialization of response bodies.

  • Retrofit: a type-safe HTTP client for the JVM from Square, built on top of OkHttp. Retrofit lets you create a client interface declaratively and has support for several serialization libraries.
  • Ktor: an HTTP client from JetBrains, built entirely for Kotlin and powered by coroutines. Ktor supports various engines, serializers, and platforms.

Resolve DNS queries

Devices that run Android 10 (API level 29) and higher have built-in support for specialized DNS lookups through both cleartext lookups and DNS-over-TLS mode. The DnsResolver API provides generic, asynchronous resolution, which lets you look up SRV, NAPTR, and other record types. Parsing the response is left to the app to perform.

On devices that run Android 9 (API level 28) and lower, the platform DNS resolver supports only A and AAAA records. This lets you look up the IP addresses associated with a name but doesn't support any other record types.

For NDK-based apps, see android_res_nsend.

Encapsulate network operations with a repository

To simplify the process of performing network operations and reduce code duplication in various parts of your app, you can use the repository design pattern. A repository is a class that handles data operations and provides a clean API abstraction over some specific data or resource.

You can use Retrofit to declare an interface that specifies the HTTP method, URL, arguments, and response type for network operations, as in the following example:

Kotlin

interface UserService {
    @GET("/users/{id}")
    suspend fun getUser(@Path("id") id: String): User
}

Java

public interface UserService {
    @GET("/user/{id}")
    Call<User> getUserById(@Path("id") String id);
}

Within a repository class, functions can encapsulate network operations and expose their results. This encapsulation ensures that the components that call the repository don't need to know how the data is stored. Any future changes to how the data is stored are isolated to the repository class as well. For example, you might have a remote change such as an update to API endpoints, or you might want to implement local caching.

Kotlin

class UserRepository constructor(
    private val userService: UserService
) {
    suspend fun getUserById(id: String): User {
        return userService.getUser(id)
    }
}

Java

class UserRepository {
    private UserService userService;

    public UserRepository(
            UserService userService
    ) {
        this.userService = userService;
    }

    public Call<User> getUserById(String id) {
        return userService.getUser(id);
    }
}

To avoid creating an unresponsive UI, don't perform network operations on the main thread. By default, Android requires you to perform network operations on a thread other than the main UI thread. If you try to perform network operations on the main thread, a NetworkOnMainThreadException is thrown.

In the previous code example, the network operation isn't actually triggered. The caller of the UserRepository must implement the threading either using coroutines or using the enqueue() function. For more information, see the codelab Get data from the internet, which demonstrates how to implement threading using Kotlin coroutines.

Survive configuration changes

When a configuration change occurs, such as a screen rotation, your fragment or activity is destroyed and recreated. Any data not saved in the instance state for your fragment activity, which can only hold small amounts of data, is lost. If this occurs, you might need to make your network requests again.

You can use a ViewModel to let your data survive configuration changes. The ViewModel component is designed to store and manage UI-related data in a lifecycle-conscious way. Using the preceding UserRepository, the ViewModel can make the necessary network requests and provide the result to your fragment or activity using LiveData:

Kotlin

class MainViewModel constructor(
    savedStateHandle: SavedStateHandle,
    userRepository: UserRepository
) : ViewModel() {
    private val userId: String = savedStateHandle["uid"] ?:
        throw IllegalArgumentException("Missing user ID")

    private val _user = MutableLiveData<User>()
    val user = _user as LiveData<User>

    init {
        viewModelScope.launch {
            try {
                // Calling the repository is safe as it moves execution off
                // the main thread
                val user = userRepository.getUserById(userId)
                _user.value = user
            } catch (error: Exception) {
                // Show error message to user
            }

        }
    }
}

Java

class MainViewModel extends ViewModel {

    private final MutableLiveData<User> _user = new MutableLiveData<>();
    LiveData<User> user = (LiveData<User>) _user;

    public MainViewModel(
            SavedStateHandle savedStateHandle,
            UserRepository userRepository
    ) {
        String userId = savedStateHandle.get("uid");
        Call<User> userCall = userRepository.getUserById(userId);
        userCall.enqueue(new Callback<User>() {
            @Override
            public void onResponse(Call<User> call, Response<User> response) {
                if (response.isSuccessful()) {
                    _user.setValue(response.body());
                }
            }

            @Override
            public void onFailure(Call<User> call, Throwable t) {
                // Show error message to user
            }
        });
    }
}

To learn more about this topic, see the following related guides: