Android上的NullPointerException异常加载器/ asynctaskloader

Question

制作twitter android应用程序。试图使OAuth工作。尝试初始化使用者时，我收到nullpointerexception。

这是我的主要活动，加上asynctaskloader类：

public class MainActivity extends FragmentActivity implements LoaderManager.LoaderCallbacks{ 

final String TAG = getClass().getName(); 

private OAuthConsumer consumer; 
private OAuthProvider provider; 
private String token; 
private String secret; 
private getCommonsHttpOAuthConsumer consumerLoader; 

Activity context; 


@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    Button signInButton = (Button) findViewById(R.id.signInButton); 

    signInButton.setOnClickListener(new View.OnClickListener() { 

     public void onClick(View v) { 
      // TODO Auto-generated method stub 
      sign_in(); 
     } 
    });  
} 


public void sign_in() 
{ 
    try { 

     Log.i(TAG, "test"); 

     this.consumer = (OAuthConsumer) getSupportLoaderManager().initLoader(0, null, this); //here's the error 

     Log.i(TAG, "test2"); 
    } catch (Exception e) { 
     Log.e(TAG, "Error creating consumer/provider",e); 
    }  
} 


@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.activity_main, menu); 
    return true; 
} 


@Override 
public android.support.v4.content.Loader onCreateLoader(int id, Bundle arg1) { 
    consumerLoader = new getCommonsHttpOAuthConsumer(context); 
    return consumerLoader; 
} 


@Override 
public void onLoadFinished(android.support.v4.content.Loader arg0, 
     Object arg1) { 
    // TODO Auto-generated method stub 

} 


@Override 
public void onLoaderReset(android.support.v4.content.Loader arg0) { 
    // TODO Auto-generated method stub 

} 

} 





class getCommonsHttpOAuthConsumer extends AsyncTaskLoader<OAuthConsumer>{ 

public getCommonsHttpOAuthConsumer(Context context) { 
    super(context); 
    // TODO Auto-generated constructor stub 
} 

@Override 
public OAuthConsumer loadInBackground() { 
    // TODO Auto-generated method stub 

    return new CommonsHttpOAuthConsumer(Constants.CONSUMER_KEY, Constants.CONSUMER_SECRET); 
} 

} 

这里是我的logcat：

04-16 13:03:54.976: I/com.example.twittertestnewapi.MainActivity(22476): test 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): Error  creating consumer/provider 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): java.lang.NullPointerException 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.support.v4.content.Loader.<init>(Loader.java:91) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.support.v4.content.AsyncTaskLoader.<init>(AsyncTaskLoader.java:92) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at com.example.twittertestnewapi.getCommonsHttpOAuthConsumer.<init>(MainActivity.java:115) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at com.example.twittertestnewapi.MainActivity.onCreateLoader(MainActivity.java:87) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.support.v4.app.LoaderManagerImpl.createLoader(LoaderManager.java:490) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.support.v4.app.LoaderManagerImpl.createAndInstallLoader(LoaderManager.java:499) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.support.v4.app.LoaderManagerImpl.initLoader(LoaderManager.java:553) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at com.example.twittertestnewapi.MainActivity.sign_in(MainActivity.java:68) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at com.example.twittertestnewapi.MainActivity$1.onClick(MainActivity.java:56) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.view.View.performClick(View.java:4204) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.view.View$PerformClick.run(View.java:17355) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.os.Handler.handleCallback(Handler.java:725) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.os.Handler.dispatchMessage(Handler.java:92) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.os.Looper.loop(Looper.java:137) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at android.app.ActivityThread.main(ActivityThread.java:5041) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at java.lang.reflect.Method.invokeNative(Native Method) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at java.lang.reflect.Method.invoke(Method.java:511) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
04-16 13:03:54.986: E/com.example.twittertestnewapi.MainActivity(22476): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

你不初始化您用Loader使用context变量。在onCreate()方法中加入：

context = this;