RoboGuice提供錯誤

Question

我正在使用RoboGuice Providers來注入自定義依賴項。我有兩個提供者第一個提供了Facebook AccessToken，第二個提供了一個需要訪問令牌的Facebook實例，因此我使用第一個提供者注入它。

public class FacebookAccessTokenProvider implements Provider<AccessToken>{ 
    @Inject FBAccountDao dao; 

    public AccessToken get() 
    { 
     List<FacebookAccount> accounts = null; 

     dao.open(); 
     accounts = dao.findAll(); 
     dao.close(); 
     if (accounts != null && !accounts.isEmpty()) 
     { 
      FacebookAccount account = accounts.get(0); 
      return new AccessToken(account.getToken(), account.getExpires()); 
     } 
     return null; 
    } 
} 

public class FacebookProvider implements Provider<Facebook>{ 

@Inject private AccessToken accessToken; 

public Facebook get() 
{ 

    if (accessToken != null) 
    { 
     Facebook facebook = new FacebookFactory().getInstance(); 
     facebook.setOAuthAppId(AppCredentials.FACEBOOK_APP_ID,AppCredentials.FACEBOOK_APP_SECRET); 
     facebook.setOAuthPermissions(AppCredentials.FACEBOOK_PERMISSION); 
     facebook.setOAuthAccessToken(accessToken); 

     return facebook; 
    } 
    return null; 
} 

} 

模塊：

public void configure(Binder binder) 
{ 
    binder.bind(FBAccountDao.class).toProvider(FBAccountDaoProvider.class); 
    binder.bind(TwitterAccountDao.class).toProvider(TwitterAccountDaoProvider.class); 
    binder.bind(TwitterFriendDao.class).toProvider(TwitterFriendDaoProvider.class); 
    binder.bind(FeedDao.class).toProvider(FeedDaoProvider.class); 
    binder.bind(Facebook.class).toProvider(FacebookProvider.class); 
    binder.bind(Token.class).toProvider(TwitterAccessTokenProvider.class); 
    binder.bind(Twitter.class).toProvider(TwitterProvider.class); 
    binder.bind(AccessToken.class).toProvider(FacebookAccessTokenProvider.class); 
} 

問題是，當我運行它crashs，並顯示以下錯誤的應用程序：

java.lang.RuntimeException: Unable to start service com.soulfeed.service.FeedService@422368d8 with Intent { cmp=com.soulfeed/.service.FeedService (has extras) }: com.google.inject.ProvisionException: Guice provision errors: 

1) null returned by binding at com.soulfeed.module.RoboGuiceModule.configure(RoboGuiceModule.java:34) 
but com.soulfeed.module.FacebookProvider.accessToken is not @Nullable 
while locating com.soulfeed.module.FacebookAccessTokenProvider 
while locating facebook4j.auth.AccessToken 
for field at com.soulfeed.module.FacebookProvider.accessToken(Unknown Source) 
while locating com.soulfeed.module.FacebookProvider 
while locating facebook4j.Facebook 

1 error 
at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2553) 
at android.app.ActivityThread.access$2000(ActivityThread.java:134) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:4867) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774) 
at dalvik.system.NativeStart.main(Native Method) 
Caused by: com.google.inject.ProvisionException: Guice provision errors: 

1) null returned by binding at com.soulfeed.module.RoboGuiceModule.configure(RoboGuiceModule.java:34) 
but com.soulfeed.module.FacebookProvider.accessToken is not @Nullable 
while locating com.soulfeed.module.FacebookAccessTokenProvider 
while locating facebook4j.auth.AccessToken 
for field at com.soulfeed.module.FacebookProvider.accessToken(Unknown Source) 
while locating com.soulfeed.module.FacebookProvider 
while locating facebook4j.Facebook 

1 error 
at com.google.inject.internal.InjectorImpl$4.get(InjectorImpl.java:987) 
at com.google.inject.internal.InjectorImpl.getInstance(InjectorImpl.java:1013) 
at roboguice.inject.ContextScopedRoboInjector.getInstance(ContextScopedRoboInjector.java:143) 
at com.soulfeed.request.AsyncRequestTask.<init>(AsyncRequestTask.java:64) 
at com.soulfeed.request.FeedAsyncTask.<init>(FeedAsyncTask.java:33) 
at com.soulfeed.service.FeedService.onStartCommand(FeedService.java:57) 
at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2536) 
... 10 more 
com.google.inject.ProvisionException: Guice provision errors: 

1) null returned by binding at com.soulfeed.module.RoboGuiceModule.configure(RoboGuiceModule.java:34) 
but com.soulfeed.module.FacebookProvider.accessToken is not @Nullable 
while locating com.soulfeed.module.FacebookAccessTokenProvider 
while locating facebook4j.auth.AccessToken 
for field at com.soulfeed.module.FacebookProvider.accessToken(Unknown Source) 
while locating com.soulfeed.module.FacebookProvider 
while locating facebook4j.Facebook 

1 error 
at com.google.inject.internal.InjectorImpl$4.get(InjectorImpl.java:987) 
at com.google.inject.internal.InjectorImpl.getInstance(InjectorImpl.java:1013) 
at roboguice.inject.ContextScopedRoboInjector.getInstance(ContextScopedRoboInjector.java:143) 
at com.soulfeed.request.AsyncRequestTask.<init>(AsyncRequestTask.java:64) 
at com.soulfeed.request.FeedAsyncTask.<init>(FeedAsyncTask.java:33) 
at com.soulfeed.service.FeedService.onStartCommand(FeedService.java:57) 
at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2536) 
at android.app.ActivityThread.access$2000(ActivityThread.java:134) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:4867) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774) 
at dalvik.system.NativeStart.main(Native Method) 

Answer 1

一般來說這是不好的做法，從Provider迴歸null 。 JavaDoc的get()甚至說「絕對不能返回null」。然而，無論如何它確實有效，但是您需要註釋FacebookProvider.accessToken和@Nullable，讓Guice允許注入null。