Android：OnSharedPreferenceChangeListener拋出空指針異常

我掙扎着爲什麼我註冊這個偵聽器時得到這個異常，我找不到它。Android：OnSharedPreferenceChangeListener拋出空指針異常

這個問題似乎是prefs.registerOnSharedPreferenceChangeListener(listener);但我找不到解決方案！

的代碼如下：

public class MtprojectActivity extends Activity { 

public void onCreate(Bundle savedInstanceState) { 
[...] 
OnSharedPreferenceChangeListener listener = new SharedPreferences.OnSharedPreferenceChangeListener() { 
      public void onSharedPreferenceChanged(SharedPreferences prefs, 
        String key) { 
       if (key.equals("CALLS_FREQUENCY_PREF")) { 
        newCallsFrequencyValue = Integer.parseInt(prefs.getString(Preferences.CALLS_FREQUENCY_PREF, "0")); 

       } else if (key.equals("SMS_FREQUENCY_PREF")) { 
        newSmsFrequencyValue = Integer.parseInt(prefs.getString(Preferences.SMS_FREQUENCY_PREF, "0")); 

       } else if (key.equals("LOC_FREQUENCY_PREF")) { 
        newLocationFrequencyValue = Integer.parseInt(prefs.getString(Preferences.LOCATION_FREQUENCY_PREF, "0")); 
       } 
      } 
     }; 

     prefs.registerOnSharedPreferenceChangeListener(listener);

這是異常跟蹤：

08-10 15:31:39.537: ERROR/AndroidRuntime(547): FATAL EXCEPTION: main 
08-10 15:31:39.537: ERROR/AndroidRuntime(547): java.lang.RuntimeException: Unable to start activity ComponentInfo{app.mtproject/app.mtproject.MtprojectActivity}: java.lang.NullPointerException 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.os.Handler.dispatchMessage(Handler.java:99) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.os.Looper.loop(Looper.java:130) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at java.lang.reflect.Method.invokeNative(Native Method) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at java.lang.reflect.Method.invoke(Method.java:507) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at dalvik.system.NativeStart.main(Native Method) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547): Caused by: java.lang.NullPointerException 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at app.mtproject.MtprojectActivity.onCreate(MtprojectActivity.java:88) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
08-10 15:31:39.537: ERROR/AndroidRuntime(547):  ... 11 more

非常感謝提前！

來源

2011-08-10 noloman

好吧，只要確保可變prefs已經包含從活動獲取的SharedPreferences之前正確地被稱爲=）

來源

2011-08-10 16:20:54 noloman

我認爲你必須與接口類：OnSharedPreferenceChangeListener

來源

2011-08-10 16:23:31 Guillaume

它只是我沒」 t實例化'prefs'變量 – noloman

Android：OnSharedPreferenceChangeListener拋出空指針異常

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