Question

我有一个Android应用程序试图从SQLite数据库加载blob作为字节数组：

public byte[] getBytesForId(long id){
    byte[] result = null;
    String sql =  "SELECT _blob FROM test_table WHERE _id=?";
    String[] selection = new String[] { String.valueOf(id) };

    Cursor mCursor = super.DB().rawQuery(sql, selection);

    if ( mCursor != null && mCursor.moveToFirst() ) {               
        if (mCursor.getCount() > 0)
            result = mCursor.getBlob(0);

        if (mCursor != null && !mCursor.isClosed())
            mCursor.close();
    }

    return result;
}

但我得到以下例外：

Failed to read row 0, column 0 from a CursorWindow which has 0 rows, 1 columns.
java.lang.IllegalStateException: Couldn't read row 0, col 0 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.
at android.database.CursorWindow.nativeGetBlob(Native Method)
at android.database.CursorWindow.getBlob(CursorWindow.java:404)
at android.database.AbstractWindowedCursor.getBlob(AbstractWindowedCursor.java:45)
at com.test.testapp.model.DbClass.getBytesForId(DbClass.java:218)
at com.test.testapp.TestService.StepThroughBlocks(TestService.java:434)
at com.test.testapp.TestService.checkBlocks(TestService.java:378)
at com.test.testapp.TestService.access$4(TestService.java:357)
at com.test.testapp.TestService$2.run(TestService.java:315)
at java.lang.Thread.run(Thread.java:841)

当然，如果我先检查光标是否有某些数据......

if ( mCursor != null && mCursor.moveToFirst() ) 
        if (mCursor.getCount() > 0)
            result = mCursor.getBlob(0);

......我不应该得到这个例外吗？我添加了mCursor.getCount行，希望这可能有所帮助，但我仍然得到异常。这怎么可能？

无法从具有0行，1列的CursorWindow读取第0行第0列

0 个答案: