從SQL數據庫中提取數據沒有成功

Question

大家晚上好，我認爲，在我的Android數據庫中提取價值內容。

首先，我嘗試了一個設備上的應用程序（SGS3）和數據庫正確創建和popoulated查詢，但是當我嘗試從光標值調用提取，LogCat給我錯誤NullPointerExeption 。我已經閱讀了一些其他的線程，但我還沒有找到我的問題的答案。

這是創建數據庫，查詢和數據的位置代碼：

public static Cursor fetchProducts(){ //attenzione cambioato,messo static 
     return mDb.query(PositionsMetaData.POSITIONS_TABLE, null,null,null,null,null,null);    
} 

static class PositionsMetaData { 
     static final String POSITIONS_TABLE = "position"; 
     static final String ID = "_id"; 
     static final String POSITIONS_NAME_KEY = "name"; 
     static final String POSITIONS_LATITUDE_KEY = "lat"; 
     static final String POSITIONS_LONGITUDE_KEY = "lon"; 
} 

private static final String POSITIONS_TABLE_CREATE = "CREATE TABLE IF NOT EXISTS " 
       + PositionsMetaData.POSITIONS_TABLE + " (" 
       + PositionsMetaData.ID + " integer primary key autoincrement, " 
       + PositionsMetaData.POSITIONS_NAME_KEY + " text, " 
       + PositionsMetaData.POSITIONS_LATITUDE_KEY + " double not null, " 
       + PositionsMetaData.POSITIONS_LONGITUDE_KEY + " double not null); "; 

說不上來爲什麼，但是Eclipse希望光標與靜態，我不知道這爲什麼這，順便說一句，THI是數據的提取代碼：

@Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.listagps); 

     TextView nomelista=(TextView)findViewById(R.id.nomelista); 
     TextView latitudinelista=(TextView)findViewById(R.id.latitudinelista); 
     TextView longitudinelista=(TextView)findViewById(R.id.longitudinelista); 


     // CREAZIONE LISTA PUNTI GPS SU LAYOUT LISTAGPS 

     ListView posizionigps=(ListView)findViewById(R.id.listagps); 

     final listagpsdb db = new listagpsdb(getApplicationContext()); 

     db.open(); 

     Cursor c=listagpsdb.fetchProducts(); 
     startManagingCursor(c); 

     @SuppressWarnings("deprecation") 
     SimpleCursorAdapter adapter=new SimpleCursorAdapter (
       this, 
       R.layout.listagps_item, 
       c, 
       new String[]{listagpsdb.PositionsMetaData.POSITIONS_NAME_KEY,listagpsdb.PositionsMetaData.POSITIONS_LONGITUDE_KEY,listagpsdb.PositionsMetaData.POSITIONS_LATITUDE_KEY}, 
       new int []{R.id.nomelista,R.id.longitudinelista,R.id.latitudinelista}); 

     posizionigps.setAdapter(adapter); 

     int nomecol=c.getColumnIndex(listagpsdb.PositionsMetaData.POSITIONS_NAME_KEY); 
     int loncol=c.getColumnIndex(listagpsdb.PositionsMetaData.POSITIONS_LONGITUDE_KEY); 
     int lancol=c.getColumnIndex(listagpsdb.PositionsMetaData.POSITIONS_LATITUDE_KEY); 


     if(c.moveToFirst()){ 
      do { 
       nomelista.append(c.getString(nomecol)); 
       latitudinelista.append(c.getString(lancol)); 
       longitudinelista.append(c.getString(loncol)); 

      } while (c.moveToNext()); 

      } 

     db.close(); 

    } 


    } 

的logcat的給我nomelista，latitudinelista和longitudinelista，所有空但在DB都填充錯誤。

有沒有解決這個問題的建議？是不正確的光標管理還是因爲textview沒有設置數據？我已經試過我知道的永恆，但沒有成功。

非常感謝所有的想幫助我:)

問題的FULL logcat的

05-05 14:42:22.613: E/AndroidRuntime(988): FATAL EXCEPTION: main 
05-05 14:42:22.613: E/AndroidRuntime(988): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.drive.info/com.drive.info.listagps}: java.lang.NullPointerException 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.app.ActivityThread.access$600(ActivityThread.java:130) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.os.Handler.dispatchMessage(Handler.java:99) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.os.Looper.loop(Looper.java:137) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.app.ActivityThread.main(ActivityThread.java:4745) 
05-05 14:42:22.613: E/AndroidRuntime(988): at java.lang.reflect.Method.invokeNative(Native Method) 
05-05 14:42:22.613: E/AndroidRuntime(988): at java.lang.reflect.Method.invoke(Method.java:511) 
05-05 14:42:22.613: E/AndroidRuntime(988): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
05-05 14:42:22.613: E/AndroidRuntime(988): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
05-05 14:42:22.613: E/AndroidRuntime(988): at dalvik.system.NativeStart.main(Native Method) 
05-05 14:42:22.613: E/AndroidRuntime(988): Caused by: java.lang.NullPointerException 
05-05 14:42:22.613: E/AndroidRuntime(988): at com.drive.info.listagps.onCreate(listagps.java:68) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.app.Activity.performCreate(Activity.java:5008) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 
05-05 14:42:22.613: E/AndroidRuntime(988): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 
05-05 14:42:22.613: E/AndroidRuntime(988): ... 11 more 

Answer 1

您必須先膨脹R.layout.listagps_item然後用這個放大的視圖找到你的文本視圖的ViewById。

像這樣： -

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.listagps); 

LayoutInflater li = getLayoutInflater(); 
View vListItems = li.inflate(R.layout.listagps_item, null); 

    TextView nomelista=(TextView) vListItems.findViewById(R.id.nomelista); 
    TextView latitudinelista=(TextView) vListItems.findViewById(R.id.latitudinelista); 
    TextView longitudinelista=(TextView) vListItems.findViewById(R.id.longitudinelista); 


    // CREAZIONE LISTA PUNTI GPS SU LAYOUT LISTAGPS 

    ListView posizionigps=(ListView)findViewById(R.id.listagps); 

    final listagpsdb db = new listagpsdb(getApplicationContext()); 

    db.open(); 

    Cursor c=listagpsdb.fetchProducts(); 
    startManagingCursor(c); 

@SuppressWarnings("deprecation") 
    SimpleCursorAdapter adapter=new SimpleCursorAdapter (
      this, 
      vListItems, 
      c, 
      new String[]{listagpsdb.PositionsMetaData.POSITIONS_NAME_KEY,listagpsdb.PositionsMetaData.POSITIONS_LONGITUDE_KEY,listagpsdb.PositionsMetaData.POSITIONS_LATITUDE_KEY}, 
      new int []{R.id.nomelista,R.id.longitudinelista,R.id.latitudinelista}); 

    posizionigps.setAdapter(adapter); 

    int nomecol=c.getColumnIndex(listagpsdb.PositionsMetaData.POSITIONS_NAME_KEY); 
    int loncol=c.getColumnIndex(listagpsdb.PositionsMetaData.POSITIONS_LONGITUDE_KEY); 
    int lancol=c.getColumnIndex(listagpsdb.PositionsMetaData.POSITIONS_LATITUDE_KEY); 


    if(c.moveToFirst()){ 
     do { 
      nomelista.append(c.getString(nomecol)); 
      latitudinelista.append(c.getString(lancol)); 
      longitudinelista.append(c.getString(loncol)); 

     } while (c.moveToNext()); 

     } 

    db.close(); 

} 
} 

在上面的代碼什麼變i是，我已經充氣R.layout.listagps_item在一個視圖中命名vListItems和使用該視圖對象nomelista的findViewById，縱向和橫向。

另請注意，我還通過了SimplelayoutAdapter中的vListItems，內嵌了R.layout.listagps_item。

希望這會有所幫助。