non-static and static issue with caching in retrofit

Question

I want to use cache in retrofit, but I get an error because of getCacheDir();

This is my code:

public class ServiceGenerator extends AppCompatActivity {

    public static final String API_BASE_URL = "https://myapiurl.com/";

    private static HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
    private static Interceptor logging = interceptor.setLevel(HttpLoggingInterceptor.Level.BASIC);

    static File dir = getCacheDir();
    static Cache cache = new Cache(dir,10*1024*1024);
    private static OkHttpClient httpClient = new OkHttpClient.Builder()
            .cache(cache)
            .addInterceptor(logging)
            .build();

    private static Gson gson = new GsonBuilder()
            .setLenient()
            .create();
    private static Retrofit.Builder builder =
            new Retrofit.Builder()
                    .baseUrl(API_BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create(gson));

    public static <S> S createService(Class<S> serviceClass) {
        Retrofit retrofit = builder.client(httpClient).build();
        return retrofit.create(serviceClass);
    }


}

The error is "Non-static method 'getCacheDir()' cannot be referenced from a static context"

So I deleted all static variables and I get another error about createService() that it couldn't be non-static.

How can I fix this problem?

Static variables should be avoided as much as possible since they can cause memory leaks. Please provide a link to the tutorial you followed, so we have a chance of understanding what you tried to do. — Sandrogo, Feb 10 '19 at 12:09
@Sandrogo this is the retrofit tutorial :https://github.com/danbuckland/android-retrofit-example and caching tutorial : https://futurestud.io/tutorials/retrofit-2-activate-response-caching-etag-last-modified — Daniel, Feb 10 '19 at 12:13
That is a very old tutorial and looks like not a popular one. Please check this: https://medium.com/mindorks/caching-with-retrofit-store-responses-offline-71439ed32fda — Housefly, Feb 10 '19 at 12:16
@Housefly i checked that too. it was in kotlin and it wasn't a complete guide of retrofit. — Daniel, Feb 10 '19 at 12:22
Possible duplicate of ["Non-static method cannot be referenced from a static context" error](https://stackoverflow.com/questions/4922145/non-static-method-cannot-be-referenced-from-a-static-context-error) — MML, Feb 12 '19 at 14:55

jczerski · Answer 1 · 2019-02-10T13:40:19.773

getCacheDir() isn't a static method, so it can't be called by static field/method. First you must create ServiceGenerator instance. I recommend you to make all fields and methods as regular (non-static) and call them/assign them in ServiceGenerator onCreate callback.

public class ServiceGenerator extends AppCompatActivity {

    private static final String API_BASE_URL = "https://myapiurl.com/";

    private Retrofit retrofit;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        HttpLoggingInterceptor loggingInterceptor = new HttpLoggingInterceptor().setLevel(HttpLoggingInterceptor.Level.BASIC);
        Cache cache = new Cache(getCacheDir(), 10 * 1024 * 1024);
        Gson gson = new GsonBuilder()
                .setLenient()
                .create();
        OkHttpClient httpClient = new OkHttpClient.Builder()
                .cache(cache)
                .addInterceptor(loggingInterceptor)
                .build();
        retrofit = new Retrofit.Builder()
                .baseUrl(API_BASE_URL)
                .client(httpClient)
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build();
    }

    protected <S> S createService(Class<S> serviceClass) {
        return retrofit.create(serviceClass);
    }
}

Every activity which gonna extend ServiceGenerator would create a service.

Thancks for your help but i got this error when i used your code : error: non-static method ~~createService(Class~~) cannot be referenced from a static context where S is a type-variable: S extends Object declared in method ~~createService(Class)~~~~~~ — Daniel, Feb 10 '19 at 16:00
Where do you want use your service? In activity? Fragment? Service? — jczerski, Feb 10 '19 at 21:22
public class TestActivity extends ServiceGenerator { @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); final SomeService service = createService(SomeService.class); } } — jczerski, Feb 11 '19 at 09:52

score 0 · Accepted Answer · answered Feb 12 '19 at 17:18

0

After a lot of search i found out the answer is in Context

 public static <S> S createService(Class<S> serviceClass,Context mContext) {
     File dir = new File(mContext.getCacheDir(),"http-cache");
     ...
 }

answered Feb 12 '19 at 17:18

Daniel

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non-static and static issue with caching in retrofit

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