我正在尝试使用rxJava、rxAndroid、Retrofit 2和OkHTTP3从URLendpoint下载文件。我的代码无法为“可观察

致命例外：主进程：com. example.khe11e.rxdownloadfile，PID：14130 java.lang.IllegalArgumentException：无法为io.retivex创建调用适配器。可观察

build. gradle：

compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
compile 'io.reactivex.rxjava2:rxjava:2.0.4'
compile 'com.squareup.retrofit2:retrofit:2.1.0'
compile 'com.squareup.retrofit2:adapter-rxjava:2.1.0'

RetrofitInterface.java：

package com.example.khe11e.rxdownloadfile;
import io.reactivex.Observable;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.Response;
import retrofit2.http.GET;
import retrofit2.http.Streaming;
import retrofit2.http.Url;

public interface RetrofitInterface {
    // Retrofit 2 GET request for rxjava
    @Streaming
    @GET
    Observable<Response<ResponseBody>> downloadFileByUrlRx(@Url String fileUrl);
}

MainActivity.java：

package com.example.khe11e.rxdownloadfile;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import java.io.File;
import io.reactivex.Observable;
import io.reactivex.ObservableEmitter;
import io.reactivex.ObservableOnSubscribe;
import io.reactivex.Observer;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.disposables.Disposable;
import io.reactivex.functions.Function;
import io.reactivex.schedulers.Schedulers;
import okhttp3.OkHttpClient;
import okhttp3.ResponseBody;
import okio.BufferedSink;
import okio.Okio;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.adapter.rxjava.RxJavaCallAdapterFactory;

public class MainActivity extends AppCompatActivity {

Button downloadImgBtn;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    downloadImgBtn = (Button) findViewById(R.id.downloadImgBtn);
    downloadImgBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            downloadImage();
        }
    });
}

public void downloadImage(){
    RetrofitInterface downloadService = createService(RetrofitInterface.class, "https://www.nasa.gov/");
    downloadService.downloadFileByUrlRx("sites/default/files/iss_1.jpg")
            .flatMap(processResponse())
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(handleResult());
}

public <T> T createService(Class<T> serviceClass, String baseUrl){
    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(baseUrl)
            .client(new OkHttpClient.Builder().build())
            .addCallAdapterFactory(RxJavaCallAdapterFactory.create()).build();
    return retrofit.create(serviceClass);
}

public Function<Response<ResponseBody>, Observable<File>> processResponse(){
    return new Function<Response<ResponseBody>, Observable<File>>() {
        @Override
        public Observable<File> apply(Response<ResponseBody> responseBodyResponse) throws Exception {
            return saveToDiskRx(responseBodyResponse);
        }
    };
}

private Observable<File> saveToDiskRx(final Response<ResponseBody> response){
    return Observable.create(new ObservableOnSubscribe<File>() {
        @Override
        public void subscribe(ObservableEmitter<File> subscriber) throws Exception {
            String header = response.headers().get("Content-Disposition");
            String filename = header.replace("attachment; filename=", "");
            new File("/data/data/" + getPackageName() + "/images").mkdir();
            File destinationFile = new File("/data/data/" + getPackageName() + "/images/" + filename);

            BufferedSink bufferedSink = Okio.buffer(Okio.sink(destinationFile));
            bufferedSink.writeAll(response.body().source());
            bufferedSink.close();

            subscriber.onNext(destinationFile);
            subscriber.onComplete();
        }
    });
}

private Observer<File> handleResult(){
    return new Observer<File>() {
        @Override
        public void onSubscribe(Disposable d) {
            Log.d("OnSubscribe", "OnSubscribe");
        }

        @Override
        public void onNext(File file) {
            Log.d("OnNext", "File downloaded to " + file.getAbsolutePath());
        }

        @Override
        public void onError(Throwable e) {
            e.printStackTrace();
            Log.d("Error", "Error " + e.getMessage());
        }

        @Override
        public void onComplete() {
            Log.d("OnComplete", "onCompleted");
        }
    };
}
}

我尝试过添加这里提到的呼叫，所以它看起来像：

Call<Observable<Response<ResponseBody>>> downloadFileByUrlRx(@Url String fileUrl);

然而，这会导致平面地图函数出现问题，因为它找不到符号方法平面地图（Function