private void openAccountChooser() {
    try {
        AccountImporter.pickNewAccount(activityOrFragment);
    } catch (NextcloudFilesAppNotInstalledException | AndroidGetAccountsPermissionNotGranted e) {
        UiExceptionManager.showDialogForException(this, e);
    }
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    AccountImporter.onActivityResult(requestCode, resultCode, data, this, new AccountImporter.IAccountAccessGranted() {

        @Override
        public void accountAccessGranted(SingleSignOnAccount account) {
            final var context = getApplicationContext();

            // As this library supports multiple accounts we created some helper methods if you only want to use one.
            // The following line stores the selected account as the "default" account which can be queried by using
            // the SingleAccountHelper.getCurrentSingleSignOnAccount(context) method
            SingleAccountHelper.setCurrentAccount(context, account.name);

            // Get the "default" account
            SingleSignOnAccount ssoAccount = null;
            try {
                ssoAccount = SingleAccountHelper.getCurrentSingleSignOnAccount(context);
            } catch (NextcloudFilesAppAccountNotFoundException | NoCurrentAccountSelectedException e) {
                UiExceptionManager.showDialogForException(context, e);
            }

            final var nextcloudAPI = new NextcloudAPI(context, ssoAccount, new GsonBuilder().create());

            // TODO … (see code in section 4 and below)
        }
    });
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    AccountImporter.onRequestPermissionsResult(requestCode, permissions, grantResults, this);
}

// Complete example: https://github.com/nextcloud/news-android/blob/890828441ba0c8a9b90afe56f3e08ed63366ece5/News-Android-App/src/main/java/de/luhmer/owncloudnewsreader/LoginDialogActivity.java#L470-L475

// If you stored the "default" account using setCurrentAccount(…) you can get the account by using the following line:
final var ssoAccount = SingleAccountHelper.getCurrentSingleSignOnAccount(context);

// Otherwise (for multi-account support you'll have to keep track of the account names yourself. Note: this has to be the name of SingleSignOnAccount.name)
AccountImporter.getSingleSignOnAccount(context, accountName);

ssoAccount.name; // Name of the account used in the android account manager
ssoAccount.username;
ssoAccount.token;
ssoAccount.url;

public NextcloudAPI(Context context, SingleSignOnAccount account, Gson gson) {

public interface API {

    String mApiEndpoint = "/index.php/apps/news/api/v1-2/";

    @GET("user")
    Observable<UserInfo> user();

    // use ParsedResponse, in case you also need the response headers. Works currently only for Observable calls.
    @GET("user")
    Observable<ParsedResponse<UserInfo>> user();

    @POST("feeds")
    Call<List<Feed>> createFeed(@Body Map<String, Object> feedMap);

    @DELETE("feeds/{feedId}")
    Completable deleteFeed(@Path("feedId") long feedId);

    // …
}

public class ApiProvider {

    private final API mApi;

    public ApiProvider() {
        mApi = retrofit.create(API.class);
    }
}

public class ApiProvider {

    private final API mApi;

    public ApiProvider(@NonNull NextcloudAPI.ApiConnectedListener callback) {
       final var ssoAccount = SingleAccountHelper.getCurrentSingleSignOnAccount(context);
       final var nextcloudAPI = new NextcloudAPI(context, ssoAccount, new GsonBuilder().create(), callback);
       mApi = new NextcloudRetrofitApiBuilder(nextcloudAPI, API.mApiEndpoint).create(API.class);
   }
}

public class MyActivity extends AppCompatActivity {

    private NextcloudAPI mNextcloudAPI;

    @Override
    protected void onStart() {
        super.onStart();
        try {
            final var ssoAccount = SingleAccountHelper.getCurrentSingleSignOnAccount(this);
            mNextcloudAPI = new NextcloudAPI(this, ssoAccount, new GsonBuilder().create());

            // Start download of file in background thread (otherwise you'll get a NetworkOnMainThreadException)
            new Thread(this::downloadFile).start();
        } catch (NextcloudFilesAppAccountNotFoundException | NoCurrentAccountSelectedException e) {
            // TODO handle errors
        }
    }

    @Override
    protected void onStop() {
        super.onStop();
        // Close Service Connection to Nextcloud Files App and
        // disconnect API from Context (prevent Memory Leak)
        mNextcloudAPI.stop();
    }

    private void downloadFile() {
        final List<Pair<String, String>> parameters = new ArrayList<>();
        parameters.add(new QueryPair("quality", "1024p"));
        parameters.add(new Pair<>("someOtherParameter", "parameterValue"));
        
        final var nextcloudRequest = new NextcloudRequest.Builder()
                .setMethod("GET")
                .setParameter(parameters)
                .setUrl(Uri.encode("/remote.php/webdav/sample movie.mp4","/"))
                .build();

        try (final var inputStream = mNextcloudAPI.performNetworkRequest(nextcloudRequest)) {
            while(inputStream.available() > 0) {
                inputStream.read();
                // TODO do something useful with the data here..
                // like writing it to a file…?
            }
        } catch (Exception e) {
            // TODO handle errors
        }
    }
}

final List<String> depth = new ArrayList<>();
depth.add("0");
header.put("Depth", depth);

final var nextcloudRequest = new NextcloudRequest.Builder()
        .setMethod("PROPFIND")
        .setHeader(header)
        .setUrl(Uri.encode("/remote.php/webdav/" + remotePath, "/"))
        .build();

final int MIN_NEXTCLOUD_FILES_APP_VERSION_CODE = 30030052;

if (VersionCheckHelper.verifyMinVersion(context, MIN_NEXTCLOUD_FILES_APP_VERSION_CODE, FilesAppType.PROD)) {
   // Version requirement is satisfied!
}