Helper methods to check network connectivity on Android (RxJava2)

[tadej....@bjss.com]

Hi all,

assume my Android app has this amazing Retrofit API:

interface AmazingApi {
  @POST("/login")
  Single<LoginInfo> login(@Body LoginBody body);
 
  @POST("/logout")
  Completable logout(@Body LogoutBody body);

  @GET("/cool/{things}")
  Observable<String> things(@Path("things") String things);

  @GET("/gazillion/cool/{things}")
  Flowable<String> gazillionThings(@Path("things") String things);
}

Before executing any of the methods, I’d like to check if network is available. As I have multiple source types (Single, Completable, etc.) I’ve implemented the following helper methods: 

private <T> Single<T> withNetworkCheck(@NonNull Single<T> continuation) {
  if (isOnline(context)) {
    return continuation.onErrorResumeNext(throwable -> {
      return Single.error(asHttpThrowable(throwable));
    });
  }
  final String err = context.getString(R.string.offline);
  return Single.error(new Throwable(err));
}
 
private <T> Observable<T> withNetworkCheck(@NonNull Observable<T> continuation) {
  // Same impl. as above, but Observable instead of Single.
}


private Completable withNetworkCheck(@NonNull Completable continuation) {
  // Same impl. as above, but Completable instead of Single.
}

// etc.

This yields the following calls:

withNetworkCheck(api.login(body));
withNetworkCheck(api.logout(body));
withNetworkCheck(api.things("foo"));

which is alright, but I'm not too happy with the amount of duplication in the helper methods.

Being relatively unexperienced with RxJava, I’m sure there’s a better/more elegant way of doing the above. Any help/hints?

Thanks!

[Joshua Pierce]

I know you are looking for an Rx solution but since you mentioned that you are using Retrofit...

Why not just make the network check part of the network flow? I assume you want to check connectivity before every request?  And since you're just throwing an error, you can easily create a custom interceptor that will do exactly that:

class CheckConnectivityInterceptor(private val connMan: ConnectivityManager) : Interceptor {

 @Throws(IOException::class)
 override fun intercept(chain: Interceptor.Chain): Response {

 val netInfo = connMan.activeNetworkInfo
 if (netInfo == null || !netInfo.isConnected) {
 throw NoNetworkException()
 }

 return chain.proceed(chain.request())
 }
}

class NoNetworkException : IOException()

To use this you just instantiate it when you create your Retrofit instance (by adding it to an anonymous OkHttp client):

Retrofit.Builder()
 .baseUrl(baseUrl)
 .client(
   OkHttpClient.Builder()
     .addInterceptor(CheckConnectivityInterceptor())
     .build()
 )
 ...finish building here...
 .build()

Now you will receive NoNetworkException in onError when there is no connection.