andretietz

class WrappingCallAdapter<RETURN_TYPE> implements CallAdapter<RETURN_TYPE> {

    private final CallAdapter<RETURN_TYPE> adapter;
    private final Map<Integer, String> registration;
    private final String info;

    WrappingCallAdapter(CallAdapter<RETURN_TYPE> adapter, Map<Integer, String> reg, String info) {
        this.adapter = adapter;
        this.registration = reg;
        this.info = info;

andretietz

class CustomAnnotationCallAdapterFactory extends CallAdapter.Factory {

    private final List<CallAdapter.Factory> callAdapterFactories;
    private final Map<Integer, String> registration;

    CustomAnnotationCallAdapterFactory(List<CallAdapter.Factory> callAdapterFactories, 
                                                                 Map<Integer, String> reg) {
        this.callAdapterFactories = callAdapterFactories;
        this.registration = reg;
    }

andretietz

@Target(METHOD)
@Retention(RUNTIME)
public @interface CustomAnnotation {
    String[] value();
}

andretietz

class CustomAnnotationInterceptor implements Interceptor {
    private final Map<Integer, String> registration;

    public CustomAnnotationInterceptor(Map<Integer, String> reg) {
        this.registration = reg;
    }

    private Integer identify(Request request) {
        // make sure this is the same method you use in the CallAdapter
        return (request.url() + request.method()).hashCode();

andretietz

package retrofit2;

import java.util.concurrent.Executor;

import retrofit2.CallAdapter.Factory;

public final class Retrofit2Platform {

    private Retrofit2Platform() {
    }

andretietz

// use SparseArray on android! I just did this to make clear what happens here
Map<Integer, String> annotationRegistration = new HashMap<>();
List<CallAdapter.Factory> factories = new ArrayList<>();
// add all your CallAdapter.Factories here
factories.add(...)
// add default CallAdapter as the last item. This is mandatory!
factories.add(Retrofit2Platform.defaultCallAdapterFactory(null));

CustomAnnotationCallAdapterFactory callAdapterFactory = 
    new CustomAnnotationCallAdapterFactory(factories, annotationRegistration);

andretietz

public class YourApplication extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        SomeLibrary.init(this);
        SomeOtherLibrary.init(this);
    }
}

andretietz

public final class YourLibraryInitProvider extends ContentProvider {

    ...

    @Override
    public void attachInfo(Context context, ProviderInfo providerInfo) {
        if (providerInfo == null) {
            throw new NullPointerException("YourLibraryInitProvider ProviderInfo cannot be null.");
        }
        // So if the authorities equal the library internal ones, the developer forgot to set his applicationId

andretietz

<manifest package="some.library.packagename"
          xmlns:android="http://schemas.android.com/apk/res/android">
    <application>
        <provider
            android:authorities="${applicationId}.yourlibraryinitprovider"
            android:exported="false"
            android:enabled="true"
            android:name=".YourLibraryInitProvider" />
    </application>

andretietz

public final class YourLibraryInitProvider extends ContentProvider {

    public YourLibraryInitProvider() {
    }

    @Override
    public boolean onCreate() {
        // get the context (Application context)
        Context context = getContext();
        // initialize whatever you need