无法读取第0行,第-1列

Question

我正在尝试复制我使用SQLite管理器创建的数据库,其中我做了:

CREATE TABLE "android_metadata" ("locale" TEXT DEFAULT 'en_US')

和

INSERT INTO "android_metadata" VALUES ('en_US')  

我将所有主键命名为_id.我的数据库被复制(在第一次运行时,logcat中有各种红色消息); 此后,它只在我查询时出错.

主要活动

public class MainActivity extends Activity {
String CNAME=" ques",TABLE_NAME=" JAVAQ";




@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Setupdb dbobj=new Setupdb(this); 

    try {    

        //dbobj.close();
        dbobj.createDataBase();

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } 



    dbobj.openDataBase();
    dbobj.close();



   try{
         SQLiteDatabase sqdb=dbobj.getReadableDatabase();



         Cursor c = sqdb.query(TABLE_NAME,
                 new String[] { CNAME },
                 null, null, null, null, null); 
         while (c.moveToNext()) {

            String name =
            c.getString(c.getColumnIndex(CNAME));
            Log.i("LOG_TAG", " HAS NAME " + name);
         }}



            catch(Exception e){

                Log.e("err", e.toString());
            } 




}}

Setupdb

public class Setupdb extends SQLiteOpenHelper {

  private static String DB_PATH = "";
    private static final String DB_NAME = "camprep.sqlite";
    private SQLiteDatabase myDataBase;
    private final Context myContext;

    private static Setupdb mDBConnection;


public Setupdb(Context context) {
    super(context, DB_NAME, null, 3);
    this.myContext=context;
    DB_PATH="/data/data/"
            + context.getApplicationContext().getPackageName()
            + "/databases/";
    Log.e(DB_NAME, DB_PATH);
}
public static synchronized Setupdb getDBAdapterInstance(Context context) {
    if (mDBConnection == null) {
        mDBConnection = new Setupdb(context);
    }
    return mDBConnection;
} 

    public void createDataBase() throws IOException {

        boolean dbExist = checkDataBase();
        if (dbExist) {
            Log.e("db","exist");
            // do nothing - database already exist
        } else {
            // By calling following method
            // 1) an empty database will be created into the default system path of your application
            // 2) than we overwrite that database with our database.
            this.getReadableDatabase();
            try {
                Log.e("calling", "copy");
                copyDataBase(); 
            } catch (IOException e) {
                throw new Error("Error copying database");
            }
        }





}
    private boolean checkDataBase() {
        SQLiteDatabase checkDB = null;
        try {
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY);

        } catch (SQLiteException e) {
            // database does't exist yet.
        }
        if (checkDB != null) {
            checkDB.close();
        }
        return checkDB != null ? true : false; 
    }

    private void copyDataBase() throws IOException {
        // Open your local db as the input stream
    InputStream myInput = myContext.getAssets().open(DB_NAME);
        // Path to the just created empty db
    String outFileName = DB_PATH + DB_NAME; 
        // Open the empty db as the output stream
    OutputStream myOutput = new FileOutputStream(outFileName);
        // transfer bytes from the inputfile to the outputfile
    byte[] buffer = new byte[1024];
    int length;
    while ((length = myInput.read(buffer)) > 0) {
        myOutput.write(buffer, 0, length);
    }
        // Close the streams
    myOutput.flush();
    myOutput.close();
    myInput.close();
}


    public void openDataBase() throws SQLException {
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
    }
    public synchronized void close() {
        if (myDataBase != null)
            myDataBase.close();
        super.close();
    } 

@Override
public void onCreate(SQLiteDatabase db) {
    // TODO Auto-generated method stub

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {


}

}

堆栈跟踪

 08-31 20:17:05.320: I/dalvikvm(9457): threadid=3: reacting to signal 3
08-31 20:17:05.370: I/dalvikvm(9457): Wrote stack traces to '/data/anr/traces.txt'
08-31 20:17:05.451: E/camprep.sqlite(9457): /data/data/com.example.mydataexplosion/databases/
08-31 20:17:05.490: E/db(9457): exist
08-31 20:17:05.521: E/CursorWindow(9457): Failed to read row 0, column -1 from a CursorWindow which has 11 rows, 1 columns.
08-31 20:17:05.521: E/err(9457): java.lang.IllegalStateException: Couldn't read row 0, col -1 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.
08-31 20:17:05.650: D/gralloc_goldfish(9457): Emulator without GPU emulation detected.
08-31 20:17:05.650: I/dalvikvm(9457): threadid=3: reacting to signal 3
08-31 20:17:05.670: I/dalvikvm(9457): Wrote stack traces to '/data/anr/traces.txt'

Answer 1

如果你看到

failed to read row 0,column -1

这意味着您正在尝试从不存在的列中读取.

如果找不到您指定的列名,则Cursor.getColumnIndex()返回-1因此无效.

有两个原因:

1. 该列不存在.
2. 列的名称不正确.(所以不存在).

注意:使用时列的名称为CASE SENSITIVEgetColumnIndex()

在您的方案中:

 c.getString(c.getColumnIndex(CNAME));

检查CNAME变量拼写是否正确,以及该名称的列是否存在.

String CNAME=" ques"

那个额外的领先白色空间是否应该存在...