java - Android错误，无法实例化服务...接口(interface)无法实例化

Question

我在 Nexus 4 上运行 Android 应用程序时遇到错误:

cannot instantiate service ... interface ... cannot be instantiated

网上查了无数遍，除了提示接口(interface)无法实例化之外，没有找到解决办法。但我不知道如何解决它。

我的应用程序只需成为可由 Muzei 应用程序调用的服务(一种插件)即可。

此应用程序基于 Muzei 的示例:https://github.com/romannurik/muzei/tree/master/example-source-500px

预先感谢您的帮助!

Config.java

public interface Config {
    public static final String API_KEY = "xxx";
}

ArtSource.java

import java.util.Random;

import package.name.muzei.MuzeiService.Photo;
import package.name.muzei.MuzeiService.PhotosResponse;

import retrofit.ErrorHandler;
import retrofit.RequestInterceptor;
import retrofit.RestAdapter;
import retrofit.RetrofitError;
import android.content.Intent;
import android.net.Uri;
import android.text.TextUtils;
import android.util.Log;

import com.google.android.apps.muzei.api.Artwork;
import com.google.android.apps.muzei.api.RemoteMuzeiArtSource;

public class ArtSource extends RemoteMuzeiArtSource {
    private static final String TAG = "App";
    private static final String SOURCE_NAME = "ArtSource";

    private static final int ROTATE_TIME_MILLIS = 3 * 60 * 60 * 1000; // rotate every 3 hours

    public ArtSource() {
        super(SOURCE_NAME);
    }

    @Override
    public void onCreate() {
        super.onCreate();
        setUserCommands(BUILTIN_COMMAND_ID_NEXT_ARTWORK);
    }

    @Override
    protected void onTryUpdate(int reason) throws RetryException {
        String currentToken = getCurrentArtwork() != null ? getCurrentArtwork().getToken() : null;

        @SuppressWarnings("deprecation")
        RestAdapter restAdapter = new RestAdapter.Builder()
        .setServer("http://url.com")
        .setRequestInterceptor(new RequestInterceptor() {
            public void intercept(RequestFacade request) {
                request.addQueryParam("key", Config.API_KEY);
            }
        })
        .setErrorHandler(new ErrorHandler() {
            public Throwable handleError(RetrofitError retrofitError) {
                int statusCode = retrofitError.getResponse().getStatus();
                if (retrofitError.isNetworkError()
                        || 500 <= statusCode && statusCode < 600) {
                    return new RetryException();
                }
                scheduleUpdate(System.currentTimeMillis() + ROTATE_TIME_MILLIS);
                return retrofitError;
            }
        })
        .build();

        MuzeiService service = restAdapter.create(MuzeiService.class);
        PhotosResponse response = service.getPopularPhotos();

        if (response == null || response.photos == null) {
            throw new RetryException();
        }

        if (response.photos.size() == 0) {
            Log.w(TAG, "No photos returned from API.");
            scheduleUpdate(System.currentTimeMillis() + ROTATE_TIME_MILLIS);
            return;
        }

        Random random = new Random();
        Photo photo;
        String token;
        while (true) {
            photo = response.photos.get(random.nextInt(response.photos.size()));
            token = Integer.toString(photo.id);
            if (response.photos.size() <= 1 || !TextUtils.equals(token, currentToken)) {
                break;
            }
        }

        publishArtwork(new Artwork.Builder()
        .title(photo.name)
        .byline(photo.user.fullname)
        .imageUri(Uri.parse(photo.image_url))
        .token(token)
        .viewIntent(new Intent(Intent.ACTION_VIEW,
                Uri.parse(photo.image_url)))
                .build());

        scheduleUpdate(System.currentTimeMillis() + ROTATE_TIME_MILLIS);
    }
}

MuzeiService.java

import java.util.List;

import retrofit.http.GET;

interface MuzeiService {
    @GET("/xxx?xxx=xxx")
    PhotosResponse getPopularPhotos();

    static class PhotosResponse {
        List<Photo> photos;
    }

    static class Photo {
        int id;
        String image_url;
        String folder;
        String name;
        User user;
    }

    static class User {
        String fullname;
    }
}

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package=""
    android:versionCode="62"
    android:versionName="1.0.9" android:installLocation="internalOnly">

    <uses-sdk
        android:minSdkVersion="14"
        android:targetSdkVersion="19" />

    <uses-permission android:name="android.permission.INTERNET" />

    <!-- Required by RemoteMuzeiArtSource -->
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />

    <application android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name">

        <service android:name=".MuzeiService"
            android:label="@string/source_name"
            android:description="@string/source_description"
            android:icon="@drawable/ic_launcher">
            <intent-filter>
                <action android:name="com.google.android.apps.muzei.api.MuzeiArtSource" />
            </intent-filter>
            <meta-data android:name="color" android:value="#fa0" />
        </service>

    </application>

</manifest>

strings.xml

<resources>
    <string name="app_name">App - Muzei extension</string>
    <string name="source_name">App</string>
    <string name="source_description">App description</string>
</resources>

包含的库

• muzei-api-1.0.jar
• muzei-api-1.0-javadoc.jar
• retrofit-1.5.1.jar

Logcat 错误

06-05 22:56:42.087: E/AndroidRuntime(21599): FATAL EXCEPTION: main
06-05 22:56:42.087: E/AndroidRuntime(21599): Process: package.name, PID: 21599
06-05 22:56:42.087: E/AndroidRuntime(21599): java.lang.RuntimeException: Unable to instantiate service package.name.muzei.MuzeiService: java.lang.InstantiationException: interface package.name.muzei.MuzeiService cannot be instantiated
06-05 22:56:42.087: E/AndroidRuntime(21599):    at android.app.ActivityThread.handleCreateService(ActivityThread.java:2556)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at android.app.ActivityThread.access$1800(ActivityThread.java:135)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at android.os.Handler.dispatchMessage(Handler.java:102)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at android.os.Looper.loop(Looper.java:136)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at android.app.ActivityThread.main(ActivityThread.java:5017)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at java.lang.reflect.Method.invoke(Native Method)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-05 22:56:42.087: E/AndroidRuntime(21599): Caused by: java.lang.InstantiationException: interface package.name.muzei.MuzeiService cannot be instantiated
06-05 22:56:42.087: E/AndroidRuntime(21599):    at java.lang.Class.newInstance(Class.java:1540)
06-05 22:56:42.087: E/AndroidRuntime(21599):    at android.app.ActivityThread.handleCreateService(ActivityThread.java:2553)
06-05 22:56:42.087: E/AndroidRuntime(21599):    ... 8 more

Answer 1

每当您在 AndroidManifest.xml 中声明 Service 时 - 当您启动应用程序时，它都会尝试实例化参数 android 中声明的 Service 类:名称。

具体来说，它尝试这样做:

new MuzeiService(...);

由于 MuzeiService 是一个接口(interface)(而不是一个类)，因此这将失败。

进一步阅读:http://developer.android.com/reference/android/app/Service.html#LocalServiceSample