由MapActivity引起的onResume中的NullPointerException？

Question

我只是第一次運行我的應用程序時出現此錯誤。爲什麼？任何線索？ 這裏是我的代碼：

我的方法init()獲取用戶的Facebook名稱和PIC時的toogle鈕啓用

public void onCreate(Bundle savedInstanceState) { 
    Log.i(TAG, "[ACTIVITY] onCreate"); 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    mUserPic = (ImageView) findViewById(R.id.user_pic); 
    mText = (TextView) findViewById(R.id.welcome_text); 
    mStepValueView = (TextView) findViewById(R.id.step_value); 

    // restore facebook session if exist 
    SessionStore.restore(facebook, this); 

    // Init facebook session 
    init(); 

    // inizialize pedometer 
    mStepValue = 0; 
    mPaceValue = 0; 

    // set map 
    mapView = (MapView) findViewById(R.id.mapview); 
    mapView.setBuiltInZoomControls(true); 
    mapView.setEnabled(true); 
    mapController = mapView.getController(); // get MapController 
    mapController.setZoom(MAP_ZOOM); // zoom in the map 

    // register listener for toggleButton 
    ToggleButton toggleButton = (ToggleButton) findViewById(R.id.ToggleButton); 
    toggleButton.setOnCheckedChangeListener(toggleButtonListener); 

} 

public void onResume() { 
    Log.i(TAG, "[ACTIVITY] onResume"); 
    super.onResume(); 
    if (!facebook.isSessionValid()) { 
     mText.setText("User offline"); 
     mUserPic.setImageBitmap(null); 
    } else { 
     facebook.extendAccessTokenIfNeeded(this, null); 
    } 

    // resume pedometer 
    mSettings = PreferenceManager.getDefaultSharedPreferences(this); 
    mPedometerSettings = new PedometerSettings(mSettings); 

    // Read from preferences if the service was running on the last onPause 
    mIsRunning = mPedometerSettings.isServiceRunning(); 

    if (mIsRunning) { 
     bindStepService(); 
    } 

    mPedometerSettings.clearServiceRunning(); 

} 

@Override 
protected void onPause() { 
    Log.i(TAG, "[ACTIVITY] onPause"); 
    // if (mIsRunning) { 
    // unbindStepService(); 
    // } 
    if (mQuitting) { 
     mPedometerSettings.saveServiceRunningWithNullTimestamp(mIsRunning); 
    } else { 
     mPedometerSettings.saveServiceRunningWithTimestamp(mIsRunning); 
    } 

    super.onPause(); 
} 

logcat的

我啓動服務

06-27 11:48:54.101: E/AndroidRuntime(20313): FATAL EXCEPTION: main 
06-27 11:48:54.101: E/AndroidRuntime(20313): java.lang.RuntimeException: Unable to resume activity {it.univpm.dii.socialfoot/it.univpm.dii.socialfoot.SocialFootActivity}: java.lang.NullPointerException 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2455) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2483) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1176) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.os.Handler.dispatchMessage(Handler.java:99) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.os.Looper.loop(Looper.java:137) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.app.ActivityThread.main(ActivityThread.java:4437) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at java.lang.reflect.Method.invokeNative(Native Method) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at java.lang.reflect.Method.invoke(Method.java:511) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at dalvik.system.NativeStart.main(Native Method) 
06-27 11:48:54.101: E/AndroidRuntime(20313): Caused by: java.lang.NullPointerException 
06-27 11:48:54.101: E/AndroidRuntime(20313): at com.google.android.maps.MapActivity.onResume(MapActivity.java:451) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at it.univpm.dii.socialfoot.SocialFootActivity.onResume(SocialFootActivity.java:296) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1154) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.app.Activity.performResume(Activity.java:4545) 
06-27 11:48:54.101: E/AndroidRuntime(20313): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2445) 
06-27 11:48:54.101: E/AndroidRuntime(20313): ... 10 more 

Answer 1

看起來Facebook可能null there ...... 試試這個

public void onResume() { 
    Log.i(TAG, "[ACTIVITY] onResume"); 
    super.onResume(); 
    if(null!=facebook){ ///<------------ 
    if (!facebook.isSessionValid()) { 
     mText.setText("User offline"); 
     mUserPic.setImageBitmap(null); 
    } else { 
     facebook.extendAccessTokenIfNeeded(this, null); 
    } 
}