sqlite android 查詢（游標）

Question

我開發了一個應用程序，允許用戶保存他最喜歡的兩個停車位。 它使用一項服務從 sqlite 數據庫中檢索相關的停車信息。 在數據庫中我有這個方法來找到第一個條目：

  public Cursor firstentry(){
       String select = "SELECT PREF1, PREF2 FROM parking_table WHERE id =1";
       Cursor cursor = db.rawQuery(select, null);
   return cursor;

每次我運行我的應用程序時，當服務嘗試使用以下命令調用此方法時，都會出現強制關閉錯誤：

Cursor c = dh.firstentry();

它給出了錯誤，因為當我評論它時，應用程序運行完美。

這是錯誤的 logcat：

04-08 18:56:38.673: E/AndroidRuntime(13166): FATAL EXCEPTION: Timer-0
04-08 18:56:38.673: E/AndroidRuntime(13166): java.lang.NullPointerException
04-08 18:56:38.673: E/AndroidRuntime(13166):    at stefan.testservice.ConnectionService$1.run(ConnectionService.java:64)
04-08 18:56:38.673: E/AndroidRuntime(13166):    at java.util.Timer$TimerImpl.run(Timer.java:284)
04-08 18:56:39.654: E/ActivityThread(13166): Activity stefan.testservice.TestserviceActivity has leaked IntentReceiver stefan.testservice.TestserviceActivity$2@40521b78 that was originally registered here. Are you missing a call to unregisterReceiver()?
04-08 18:56:39.654: E/ActivityThread(13166): android.app.IntentReceiverLeaked: Activity stefan.testservice.TestserviceActivity has leaked IntentReceiver stefan.testservice.TestserviceActivity$2@40521b78 that was originally registered here. Are you missing a call to unregisterReceiver()?
04-08 18:56:39.654: E/ActivityThread(13166):    at android.app.LoadedApk$ReceiverDispatcher.<init>(LoadedApk.java:756)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.app.LoadedApk.getReceiverDispatcher(LoadedApk.java:551)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.app.ContextImpl.registerReceiverInternal(ContextImpl.java:795)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.app.ContextImpl.registerReceiver(ContextImpl.java:782)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.app.ContextImpl.registerReceiver(ContextImpl.java:776)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.content.ContextWrapper.registerReceiver(ContextWrapper.java:318)
04-08 18:56:39.654: E/ActivityThread(13166):    at stefan.testservice.TestserviceActivity$1.onServiceConnected(TestserviceActivity.java:280)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.app.LoadedApk$ServiceDispatcher.doConnected(LoadedApk.java:1064)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.app.LoadedApk$ServiceDispatcher$RunConnection.run(LoadedApk.java:1081)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.os.Handler.handleCallback(Handler.java:587)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.os.Handler.dispatchMessage(Handler.java:92)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.os.Looper.loop(Looper.java:123)
04-08 18:56:39.654: E/ActivityThread(13166):    at android.app.ActivityThread.main(ActivityThread.java:3683)
04-08 18:56:39.654: E/ActivityThread(13166):    at java.lang.reflect.Method.invokeNative(Native Method)
04-08 18:56:39.654: E/ActivityThread(13166):    at java.lang.reflect.Method.invoke(Method.java:507)
04-08 18:56:39.654: E/ActivityThread(13166):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-08 18:56:39.654: E/ActivityThread(13166):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-08 18:56:39.654: E/ActivityThread(13166):    at dalvik.system.NativeStart.main(Native Method)
04-08 18:56:40.054: E/ActivityThread(13166): Activity stefan.testservice.TestserviceActivity has leaked ServiceConnection stefan.testservice.TestserviceActivity$1@40521790 that was originally bound here
04-08 18:56:40.054: E/ActivityThread(13166): android.app.ServiceConnectionLeaked: Activity stefan.testservice.TestserviceActivity has leaked ServiceConnection stefan.testservice.TestserviceActivity$1@40521790 that was originally bound here
04-08 18:56:40.054: E/ActivityThread(13166):    at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:938)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:833)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.app.ContextImpl.bindService(ContextImpl.java:867)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.content.ContextWrapper.bindService(ContextWrapper.java:347)
04-08 18:56:40.054: E/ActivityThread(13166):    at stefan.testservice.TestserviceActivity.doBindService(TestserviceActivity.java:290)
04-08 18:56:40.054: E/ActivityThread(13166):    at stefan.testservice.TestserviceActivity$DownloadTask.onPostExecute(TestserviceActivity.java:193)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.os.AsyncTask.finish(AsyncTask.java:417)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.os.AsyncTask.access$300(AsyncTask.java:127)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.os.Looper.loop(Looper.java:123)
04-08 18:56:40.054: E/ActivityThread(13166):    at android.app.ActivityThread.main(ActivityThread.java:3683)
04-08 18:56:40.054: E/ActivityThread(13166):    at java.lang.reflect.Method.invokeNative(Native Method)
04-08 18:56:40.054: E/ActivityThread(13166):    at java.lang.reflect.Method.invoke(Method.java:507)
04-08 18:56:40.054: E/ActivityThread(13166):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-08 18:56:40.054: E/ActivityThread(13166):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-08 18:56:40.054: E/ActivityThread(13166):    at dalvik.system.NativeStart.main(Native Method)

非常感謝任何幫助，因為我嘗試了一切但似乎沒有任何效果。 提前致謝！

編輯：

停車表代碼：

  public void onCreate(SQLiteDatabase db) {
     db.execSQL("CREATE TABLE " + TABLE_NAME + "(id INTEGER PRIMARY KEY, PREF1 TEXT, PREF2 TEXT)");
  }

Answer 1

它是一個nullpointerexception ，意味着當時數據庫中可能沒有任何內容。 如果 cursor 是 null，你需要處理

單步執行代碼確實是了解 null 到底是什么的唯一方法。雖然很難用您發布的內容來判斷，但肯定需要更多代碼

Answer 2

你正在運行 rawsql 所以檢查確切的查詢是否對你的數據庫有效， SELECT PREF1, PREF2 FROM parking_table WHERE id =1

PREF1 是列的名稱嗎？

Answer 3

如果您沒有 SQLite 瀏覽器軟件，請在此處獲取： SQLite 瀏覽器

當我使用 SQLite 時，它會有所幫助。我之前遇到過這個問題，我通過在查詢中添加id參數來解決它。 本質上，您需要將查詢更改為：

public Cursor firstentry(){
   String select = "SELECT id, PREF1, PREF2 FROM parking_table WHERE id =1";
   Cursor cursor = db.rawQuery(select, null);
return cursor;

如果c是 Cursor 的名稱，請不要忘記調用c.moveToFirst() 。

Answer 4

我設法解決了它，一切正常，我只需要初始化 class object。這是需要的代碼行：

this.yourobject = new class(this);

在我的例子中是：

this.dh = new SQLHelper(this);

希望能幫助到你：）