的Android PreferenceManager NullPointException

我竭力要了解使用PreferenceManager時，爲什麼我得到一個零點例外。的Android PreferenceManager NullPointException

我使用的是當前活動中一個按鈕來調用另一個名爲活性Location

/** Location selection */ 
    bLocation = (Button) findViewById(R.id.bLocation); 
    bLocation.setOnClickListener(new View.OnClickListener() { 
     public void onClick(View v) { 

      loc = new Location(); 
      loc.locationSelection(); 
     } 
    });

//上面的按鈕調用下面的類

public class Location extends Activity { 

    NetworkConnection nc; 
    SharedPreferences prefs; 
    SharedPreferences sharedPrefs; 
    NetworkConnection netConnect; 
    Options opts; 

    public void locationSelection(){ 

     try{ 
      sharedPrefs = PreferenceManager.getDefaultSharedPreferences(getApplicationContext()); 
      if (sharedPrefs.contains("LOCATION")){ 
       Log.d("if", "if"); 
      }else{ 
       Log.d("if", "else"); 

      } 

     }catch(Exception e){ 
      Log.d("EXCEPTION", "Location Selection " + e); 
     } 
    } 
}

編輯：

//全部選項類中的Location類。

public class Options extends Activity { 

    /** Include classes */ 
    SharedPreferences sharedPrefs; 
    Preferences prefs; 
    Location loc; 
    LocationSQL locSQL; 
    NetworkConnection netConnect; 

    /** Declare buttons */ 
    Button bLocation; 
    Button bRefresh; 

    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.options); 

     sharedPrefs = PreferenceManager.getDefaultSharedPreferences(Options.this); 

     /** Set the location for the user */ 
     setLocationPref(); 

     /** Refresh selection */ 
     bRefresh = (Button) findViewById(R.id.bRefresh); 
     bRefresh.setOnClickListener(new View.OnClickListener() { 
      public void onClick(View v) { 


      } 
     }); 

     /** Location selection */ 
     bLocation = (Button) findViewById(R.id.bLocation); 
     bLocation.setOnClickListener(new View.OnClickListener() { 
      public void onClick(View v) { 

       loc = new Location(); 
       loc.locationSelection(); 
      } 
     }); 
    }

//整個日誌貓

06-10 13:56:03.015: D/AndroidRuntime(27310): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<< 
06-10 13:56:03.015: D/AndroidRuntime(27310): CheckJNI is ON 
06-10 13:56:03.135: D/AndroidRuntime(27310): --- registering native functions --- 
06-10 13:56:03.685: D/dalvikvm(249): GC_EXPLICIT freed 88 objects/4296 bytes in 43ms 
06-10 13:56:03.726: D/PackageParser(59): Scanning package: /data/app/vmdl72287.tmp 
06-10 13:56:03.845: I/PackageManager(59): Removing non-system package:com.swiftdrink 
06-10 13:56:03.845: I/ActivityManager(59): Force stopping package com.swiftdrink uid=10036 
06-10 13:56:03.855: I/Process(59): Sending signal. PID: 26952 SIG: 9 
06-10 13:56:03.865: I/UsageStats(59): Unexpected resume of com.android.launcher while already resumed in com.swiftdrink 
06-10 13:56:03.875: I/WindowManager(59): WIN DEATH: Window{44f77270 com.swiftdrink/com.swiftdrink.SwiftDrinkMain paused=false} 
06-10 13:56:03.905: W/InputManagerService(59): Got RemoteException sending setActive(false) notification to pid 26952 uid 10036 
06-10 13:56:04.016: W/IInputConnectionWrapper(114): showStatusIcon on inactive InputConnection 
06-10 13:56:04.205: D/PackageManager(59): Scanning package com.swiftdrink 
06-10 13:56:04.205: I/PackageManager(59): Package com.swiftdrink codePath changed from /data/app/com.swiftdrink-1.apk to /data/app/com.swiftdrink-2.apk; Retaining data and using new 
06-10 13:56:04.215: I/PackageManager(59): /data/app/com.swiftdrink-2.apk changed; unpacking 
06-10 13:56:04.225: D/installd(34): DexInv: --- BEGIN '/data/app/com.swiftdrink-2.apk' --- 
06-10 13:56:04.435: D/dalvikvm(27317): DexOpt: load 36ms, verify 99ms, opt 2ms 
06-10 13:56:04.445: D/installd(34): DexInv: --- END '/data/app/com.swiftdrink-2.apk' (success) --- 
06-10 13:56:04.445: W/PackageManager(59): Code path for pkg : com.swiftdrink changing from /data/app/com.swiftdrink-1.apk to /data/app/com.swiftdrink-2.apk 
06-10 13:56:04.445: W/PackageManager(59): Resource path for pkg : com.swiftdrink changing from /data/app/com.swiftdrink-1.apk to /data/app/com.swiftdrink-2.apk 
06-10 13:56:04.455: D/PackageManager(59): Activities: com.swiftdrink.SplashScreen com.swiftdrink.SwiftDrinkMain com.swiftdrink.Deals com.swiftdrink.Events com.swiftdrink.Featured com.swiftdrink.Options com.swiftdrink.SortBy com.swiftdrink.NetworkConnection com.swiftdrink.Constents com.swiftdrink.getSetLocation com.swiftdrink.Location com.swiftdrink.DBAdapter com.swiftdrink.JSON com.swiftdrink.Preferences 
06-10 13:56:04.465: I/ActivityManager(59): Force stopping package com.swiftdrink uid=10036 
06-10 13:56:04.565: I/installd(34): move /data/dalvik-cache/[email protected]@[email protected] -> /data/dalvik-cache/[email protected]@[email protected] 
06-10 13:56:04.565: D/PackageManager(59): New package installed in /data/app/com.swiftdrink-2.apk 
06-10 13:56:04.685: I/ActivityManager(59): Force stopping package com.swiftdrink uid=10036 
06-10 13:56:04.835: D/dalvikvm(114): GC_EXPLICIT freed 1024 objects/58032 bytes in 140ms 
06-10 13:56:04.845: D/dalvikvm(59): GC_EXPLICIT freed 12088 objects/692712 bytes in 141ms 
06-10 13:56:05.015: W/RecognitionManagerService(59): no available voice recognition services found 
06-10 13:56:05.235: D/dalvikvm(59): GC_EXPLICIT freed 4804 objects/260184 bytes in 94ms 
06-10 13:56:05.255: D/dalvikvm(148): GC_EXPLICIT freed 2567 objects/129888 bytes in 540ms 
06-10 13:56:05.265: I/installd(34): unlink /data/dalvik-cache/[email protected]@[email protected] 
06-10 13:56:05.276: D/AndroidRuntime(27310): Shutting down VM 
06-10 13:56:05.285: D/dalvikvm(27310): Debugger has detached; object registry had 1 entries 
06-10 13:56:05.305: I/dalvikvm(27310): JNI: AttachCurrentThread (from ???.???) 
06-10 13:56:05.305: I/AndroidRuntime(27310): NOTE: attach of thread 'Binder Thread #3' failed 
06-10 13:56:05.786: D/AndroidRuntime(27322): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<< 
06-10 13:56:05.786: D/AndroidRuntime(27322): CheckJNI is ON 
06-10 13:56:05.895: D/AndroidRuntime(27322): --- registering native functions --- 
06-10 13:56:06.466: I/ActivityManager(59): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.swiftdrink/.SplashScreen } 
06-10 13:56:06.505: I/ActivityManager(59): Start proc com.swiftdrink for activity com.swiftdrink/.SplashScreen: pid=27328 uid=10036 gids={3003, 1015} 
06-10 13:56:06.535: D/AndroidRuntime(27322): Shutting down VM 
06-10 13:56:06.535: D/dalvikvm(27322): Debugger has detached; object registry had 1 entries 
06-10 13:56:06.575: I/AndroidRuntime(27322): NOTE: attach of thread 'Binder Thread #3' failed 
06-10 13:56:07.445: D/dalvikvm(27328): GC_EXTERNAL_ALLOC freed 858 objects/59096 bytes in 175ms 
06-10 13:56:07.815: I/ActivityManager(59): Displayed activity com.swiftdrink/.SplashScreen: 1333 ms (total 1333 ms) 
06-10 13:56:08.155: I/ActivityManager(59): Starting activity: Intent { act=com.swiftdrink.SWIFTDRINKMAIN cmp=com.swiftdrink/.SwiftDrinkMain } 
06-10 13:56:08.275: V/one(27328): locationSelection 
06-10 13:56:08.585: I/ActivityManager(59): Displayed activity com.swiftdrink/.SwiftDrinkMain: 428 ms (total 428 ms) 
06-10 13:56:11.646: D/SntpClient(59): request time failed: java.net.SocketException: Address family not supported by protocol 
06-10 13:56:16.886: D/dalvikvm(114): GC_EXPLICIT freed 970 objects/55696 bytes in 124ms 
06-10 13:56:20.166: D/EXCEPTION(27328): Location Selection java.lang.NullPointerException 
06-10 13:56:21.906: D/dalvikvm(260): GC_EXPLICIT freed 66 objects/3040 bytes in 128ms

編輯2： //網絡連接類

public class NetworkConnection extends Activity { 
    /** Called when the activity is first created. */ 

    public boolean isNetworkConnAvail(Context context) { 

     ConnectivityManager connMgr = (ConnectivityManager) 
      context.getSystemService(Context.CONNECTIVITY_SERVICE); 
     NetworkInfo networkInfo = connMgr.getActiveNetworkInfo(); 
     if (networkInfo != null) 
      return networkInfo.isConnected(); 

     return false; 
    } 
}

//打印statment

06-10 14:10:40.015: D/AndroidRuntime(27731): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<< 
06-10 14:10:40.015: D/AndroidRuntime(27731): CheckJNI is ON 
06-10 14:10:40.145: D/AndroidRuntime(27731): --- registering native functions --- 
06-10 14:10:40.535: D/dalvikvm(27670): GC_EXPLICIT freed 1408 objects/74352 bytes in 898ms 
06-10 14:10:40.645: D/AndroidRuntime(27731): Shutting down VM 
06-10 14:10:40.645: D/dalvikvm(27731): Debugger has detached; object registry had 1 entries 
06-10 14:10:40.665: I/AndroidRuntime(27731): NOTE: attach of thread 'Binder Thread #3' failed 
06-10 14:10:41.045: D/AndroidRuntime(27739): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<< 
06-10 14:10:41.045: D/AndroidRuntime(27739): CheckJNI is ON 
06-10 14:10:41.166: D/AndroidRuntime(27739): --- registering native functions --- 
06-10 14:10:41.655: I/ActivityManager(59): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.swiftdrink/.SplashScreen } 
06-10 14:10:41.695: D/AndroidRuntime(27739): Shutting down VM 
06-10 14:10:41.695: D/dalvikvm(27739): Debugger has detached; object registry had 1 entries 
06-10 14:10:41.775: I/dalvikvm(27739): JNI: AttachCurrentThread (from ???.???) 
06-10 14:10:41.775: I/AndroidRuntime(27739): NOTE: attach of thread 'Binder Thread #3' failed 
06-10 14:10:42.465: I/ActivityManager(59): Displayed activity com.swiftdrink/.SplashScreen: 799 ms (total 799 ms) 
06-10 14:10:42.845: I/ActivityManager(59): Starting activity: Intent { act=com.swiftdrink.SWIFTDRINKMAIN cmp=com.swiftdrink/.SwiftDrinkMain } 
06-10 14:10:42.895: V/one(27670): locationSelection 
06-10 14:10:43.186: I/ActivityManager(59): Displayed activity com.swiftdrink/.SwiftDrinkMain: 337 ms (total 337 ms) 
06-10 14:10:45.185: D/EXCEPTION(27670): Location Selection java.lang.NullPointerException 
06-10 14:10:45.185: W/System.err(27670): java.lang.NullPointerException 
06-10 14:10:45.205: W/System.err(27670): at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:100) 
06-10 14:10:45.205: W/System.err(27670): at com.swiftdrink.Location.locationSelection(Location.java:39) 
06-10 14:10:45.205: W/System.err(27670): at com.swiftdrink.Options$2.onClick(Options.java:73) 
06-10 14:10:45.205: W/System.err(27670): at android.view.View.performClick(View.java:2408) 
06-10 14:10:45.205: W/System.err(27670): at android.view.View$PerformClick.run(View.java:8816) 
06-10 14:10:45.205: W/System.err(27670): at android.os.Handler.handleCallback(Handler.java:587) 
06-10 14:10:45.216: W/System.err(27670): at android.os.Handler.dispatchMessage(Handler.java:92) 
06-10 14:10:45.216: W/System.err(27670): at android.os.Looper.loop(Looper.java:123) 
06-10 14:10:45.216: W/System.err(27670): at android.app.ActivityThread.main(ActivityThread.java:4627) 
06-10 14:10:45.216: W/System.err(27670): at java.lang.reflect.Method.invokeNative(Native Method) 
06-10 14:10:45.216: W/System.err(27670): at java.lang.reflect.Method.invoke(Method.java:521) 
06-10 14:10:45.216: W/System.err(27670): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
06-10 14:10:45.216: W/System.err(27670): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
06-10 14:10:45.226: W/System.err(27670): at dalvik.system.NativeStart.main(Native Method) 
06-10 14:10:48.366: D/dalvikvm(114): GC_EXPLICIT freed 239 objects/11320 bytes in 128ms

來源

2012-06-10 James

你可以發佈LogCat？ –

我只得到一個NullPointerException，沒有別的幫助我。 – James

在LogCat中發佈20行左右的例外。哪條線發生異常？另外，你可以發佈你正在使用的類的按鈕在其中的進口嗎？ –

通過使用loc = new Location（）創建Location類的實例。現在Location是一個擴展Activity的類，因爲你不像普通的Activity那樣啓動它（例如通過Intents），所以onCreate（）永遠不會被調用。由於這個原因，你的getApplicationContext（）將返回null，因爲你的Activity沒有按照預期被實例化。

爲了解決這個問題，你可以構造添加到類像這樣：

//New Global Variable 

Context context; 

public Location (Context arg) 
{ 
context = arg; 
}

此外，你需要改變SharedPreferences初始化使用context變量而不是getApplicationContext（）。

，然後使用分配LOC：

loc = new Location(getApplicationContext());

這應該至少解決您的NullPointerException異常。

你SocketException似乎是因爲不支持的地址類型正在發生，但是從您發佈的代碼，你似乎沒有使用任何地址都如此。

來源

2012-06-10 14:22:14

的Android PreferenceManager NullPointException

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