Question

我正在尝试从外部SDCard读取数据库它适用于我但是当我从光标获取值时它会抛出错误IndexOutOfBoundException

MyCode

public class Database{

    public static final String  DATABASE_NAME = "Test/EduTab.s3db";

    private SQLiteDatabase database;
    private File SDCardDir = Environment.getExternalStorageDirectory();

    public Database()
    {
        try
        {
            File file = new File(SDCardDir + File.separator + DATABASE_NAME);
            if(file.exists()){
                database = SQLiteDatabase.openDatabase(SDCardDir + File.separator + DATABASE_NAME, null,SQLiteDatabase.OPEN_READONLY);  
            }
        }
        catch (SQLiteException ex)
        {
            ex.printStackTrace();
        }
    }

    public SQLiteDatabase getdatabase(){
        return database;
    }
}

主要活动

public class MainActivity extends Activity {

    SQLiteDatabase mDatabase;
    Database mData = new Database();


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mDatabase = mData.getdatabase();

        Cursor mCursor = mDatabase.rawQuery("Select * From mst_Subject",null);
        String[] ColumnNames = mCursor.getColumnNames();

        Log.d("Cursor Size",""+mCursor.getCount()); // It Works Returns Size of The  Table 

        for(int row=0;row<mCursor.getCount();row++)
        {
            for(int col=0;col<ColumnNames.length;col++){

                Log.d("ColumnName",""+ColumnNames[col]); // It Works Returns The Name Of The Column
                Log.d("Column Value",mCursor.getString(mCursor.getColumnIndex(ColumnNames[col])));  // Not Working It Throw Error           

                /*
                 * Error Is 
                 * java.lang.RuntimeException: Unable to start activity
                 * ComponentInfo{com.example.readdatabasefromsdcard/com.example.
                 * readdatabasefromsdcard.MainActivity}:
                 * android.database.CursorIndexOutOfBoundsException: Index -1
                 * requested, with a size of 8
                 */

                Log.d("Record["+row+"]["+col+"]",mCursor.getString(mCursor.getColumnIndex(ColumnNames[col])));

            }
            Log.d("End Of The Record ["+row+"]","==========================================================");
        }

    }
}

Answer 1

在for循环

之前写下面的语句

mCursor.moveToFirst();

Answer 2

更改

for(int row=0;row<mCursor.getCount();row++)

到

 int row = -1;
 while (mCursor.moveToNext()) {
     row++;
     // now use cursor.getString()

光标最初位于第一行之前，没有什么可以在那里阅读

Answer 3

使用此代码：

    if(mCursor.moveToFirst())
    {
        do
        {

        }while(mCursor.moveToNext());
    }

从数据库获取数据会引发IndexOutOfBound异常

3 个答案: