如何通过IDataReader读取图像

我在窗口C＃vs05上工作。 我想通过IDataReader读取图像….在oledb ….我怎么能这样做假设我想从数据库列名学生id读取int值然后我以下面的方式编写代码

private IDataReader _reader; public int GetInt32(String sFieldName) { return (_reader[sFieldName]==DBNull.Value)? (Int32) 0 :Convert.ToInt32(_reader[sFieldName]); } 

要保存图像，请使用以下代码

  DataTable oTable = new DataTable(); oTable.Columns.Add("BoardImage"); DataRow oRow = oTable.NewRow(); oRow["BoardImage"] = oItem.BoardImage; SQL= Insert into table oRow["BoardImage"]; Now i want to read image BY Idatareader ......to do that i write bellow code but i get error message "Parameter is not valid." public Image GetImage(String sFieldName) { try { //MemoryStream stream = new MemoryStream(); //stream.Write(image, 0, image.Length); //Bitmap bitmap = new Bitmap(stream); byte[] imageData = null; long byteSize = 0; byteSize = _reader.GetBytes(_reader.GetOrdinal(sFieldName), 0, null, 0, 0); **//May be error occur here** imageData = new byte[byteSize]; long bytesread = 0; int curpos = 0, chunkSize = 500; while (bytesread < byteSize) { // chunkSize is an arbitrary application defined value bytesread += _reader.GetBytes(_reader.GetOrdinal(sFieldName), curpos, imageData, curpos, chunkSize); curpos += chunkSize; } byte[] imgData = imageData; MemoryStream ms = new MemoryStream(imgData); **//May be error occur here** Image oImage = Image.FromStream((Stream)ms); return oImage; } catch(Exception ex) { throw new Exception("Failed to get Image: " + ex.Message); } } 

任何人都可以帮助我？我的bug在哪里…..如何解决这个问题

Answer 1

尝试类似的事情（确保读者处于顺序模式）：

 using(MemoryStream ms = new MemoryStream()) { const int BUFFER_SIZE = 1024; byte[] buffer = new byte[BUFFER_SIZE]; int col = reader.GetOrdinal(fieldName), bytesRead, offset = 0; while((bytesRead = (int)reader.GetBytes(col,offset,buffer,0,BUFFER_SIZE)) > 0) { ms.Write(buffer, 0, bytesRead); offset += bytesRead; } ms.Position = 0; return Image.FromStream(ms); } 

我在原始代码中看到的最大问题是，每次调用GetBytes返回的字节数并不太多（即假设你有一个完整的块）。