Question

我正在尝试检索SQLite表中的名称，尽管数据库有11个或更多记录，当我尝试从存储的记录中检索任何名称时，应用程序。 Crashs。

Java代码：

OnClickListener btn_NavaigateListsner = new OnClickListener() {

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        if (!btn_Save.isEnabled()) {
            int c = mpoh.getCurrentRowNumber();
            Toast.makeText(getBaseContext(), ""+mpoh.getMP_Name(0), Toast.LENGTH_SHORT).show();
            Bundle bundle = new  Bundle();
            //bundle.putString("name", mpoh.getMP_Name(c));
            //bundle.putDouble("lat", mpoh.getMP_Lat(c));
            //bundle.putDouble("lng", mpoh.getMP_Lng(c));
            //bundle.putString("date", mpoh.getMP_Date(c));
            //bundle.putString("time", mpoh.getMP_Time(c));

            intent01 = new Intent(MPData.this, MPInfo.class);
            intent01.putExtras(bundle);
            startActivity(intent01);


        }// End of If
    }
};

检索存储名称的方法：

public String getMP_Name(long id) {
    SQLiteDatabase db = this.getReadableDatabase();
    SQLiteCursor c = (SQLiteCursor) db.rawQuery("SELECT name FROM MPData WHERE "+
                                                BaseColumns._ID+" = "+
                                                Long.toString(id) +" AND name IS NOT NULL ", null);
    c.moveToFirst();
    String r = c.getString(0);
    c.close();
    db.close();

    return r;       
}

LogCat的一些输出：

 03-05 12:16:48.288: E/AndroidRuntime(973): FATAL EXCEPTION: main
03-05 12:16:48.288: E/AndroidRuntime(973): android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.database.AbstractCursor.checkPosition(AbstractCursor.java:580)
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:214)
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:41)
03-05 12:16:48.288: E/AndroidRuntime(973):  at com.androidbook.MP.MP_DB.getMP_Name(MP_DB.java:45)
03-05 12:16:48.288: E/AndroidRuntime(973):  at com.androidbook.MP.MPData$1.onClick(MPData.java:57)
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.view.View.performClick(View.java:2485)
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.view.View$PerformClick.run(View.java:9080)
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.os.Handler.handleCallback(Handler.java:587)
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.os.Handler.dispatchMessage(Handler.java:92)
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.os.Looper.loop(Looper.java:130)
03-05 12:16:48.288: E/AndroidRuntime(973):  at android.app.ActivityThread.main(ActivityThread.java:3683)
03-05 12:16:48.288: E/AndroidRuntime(973):  at java.lang.reflect.Method.invokeNative(Native Method)
03-05 12:16:48.288: E/AndroidRuntime(973):  at java.lang.reflect.Method.invoke(Method.java:507)
03-05 12:16:48.288: E/AndroidRuntime(973):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-05 12:16:48.288: E/AndroidRuntime(973):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-05 12:16:48.288: E/AndroidRuntime(973):  at dalvik.system.NativeStart.main(Native Method)
03-05 12:32:19.897: E/AndroidRuntime(1022): FATAL EXCEPTION: main
03-05 12:32:19.897: E/AndroidRuntime(1022): android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.database.AbstractCursor.checkPosition(AbstractCursor.java:580)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:214)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:41)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at com.androidbook.MP.MP_DB.getMP_Name(MP_DB.java:45)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at com.androidbook.MP.MPData$1.onClick(MPData.java:57)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.view.View.performClick(View.java:2485)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.view.View$PerformClick.run(View.java:9080)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.os.Handler.handleCallback(Handler.java:587)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.os.Handler.dispatchMessage(Handler.java:92)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.os.Looper.loop(Looper.java:130)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at android.app.ActivityThread.main(ActivityThread.java:3683)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at java.lang.reflect.Method.invokeNative(Native Method)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at java.lang.reflect.Method.invoke(Method.java:507)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-05 12:32:19.897: E/AndroidRuntime(1022):     at dalvik.system.NativeStart.main(Native Method)
03-05 12:39:24.627: E/AndroidRuntime(1093): FATAL EXCEPTION: main
03-05 12:39:24.627: E/AndroidRuntime(1093): android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.database.AbstractCursor.checkPosition(AbstractCursor.java:580)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:214)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:41)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at com.androidbook.MP.MP_DB.getMP_Name(MP_DB.java:45)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at com.androidbook.MP.MPData$1.onClick(MPData.java:57)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.View.performClick(View.java:2485)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.View.onKeyUp(View.java:4257)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.widget.TextView.onKeyUp(TextView.java:4587)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.KeyEvent.dispatch(KeyEvent.java:1280)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.View.dispatchKeyEvent(View.java:3855)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:789)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:789)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:789)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:789)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchKeyEvent(PhoneWindow.java:1687)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at com.android.internal.policy.impl.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1120)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.app.Activity.dispatchKeyEvent(Activity.java:2073)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1663)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.ViewRoot.deliverKeyEventToViewHierarchy(ViewRoot.java:2560)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.ViewRoot.handleFinishedEvent(ViewRoot.java:2535)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1867)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.os.Looper.loop(Looper.java:130)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at android.app.ActivityThread.main(ActivityThread.java:3683)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at java.lang.reflect.Method.invokeNative(Native Method)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at java.lang.reflect.Method.invoke(Method.java:507)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-05 12:39:24.627: E/AndroidRuntime(1093):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

代码看起来很好。 您是否100％确定数据库中有一个条目，其中_id对应于0？

如果您使用无效的_id调用getMP_Name，则会在发布时引发异常。

您应该按如下方式检查此案例：

if (c.getCount()==0) return "";
// rest of code

但我不会这样做因为你当前的getMP_XXX实现效率非常低，因为你为每个字段和每一行点击了数据库。您应该最小化查询次数，然后迭代生成的游标。

Answer 2

请看以下一行：

String r = c.getString（0）;

您无法安全地检查光标，只是假设结果已收到。检查SQL查询并添加安全检查以确保光标已检索结果。

从数据库中检索记录时出错？

2 个答案: