Question

我似乎无法为我的真正问题得到答案Invalid parameter when retrieving image from DB所以Imma一块一块地尝试。在C＃和MS Access 2010中使用Visual Studio 2012.我的解决方案是一个非Web相关的应用程序。

我不确定这部分，所以我的问题是如何正确地从查询中获取行中的 OLE对象的图像一个字节数组（ byte [] ），因为肯定不是我用以下代码做的。我正在谈论的那一行是 row [“FOTO”] 。

                OleDbDataAdapter adapter = new OleDbDataAdapter("SELECT * FROM [APP_Equipamento_Geral] WHERE COD_ETIQ like '%" + codigo + "%'", l);
                DataSet ds = new DataSet();
                adapter.Fill(ds, "[APP_Equipamento_Geral]");
                string s = ds.Tables["[APP_Equipamento_Geral]"].Columns[16].ColumnName;
                foreach (DataRow row in ds.Tables["[APP_Equipamento_Geral]"].Rows)
                {
                    eq.NSerie = row["N_SERIE"].ToString();
                    eq.NInventario = row["Codigo"].ToString(); 

                    if (row["FOTO"] != DBNull.Value && row["FOTO"] != null)
                    {
                        string str = row["FOTO"].ToString();
                        byte[] b = stringToByteArray(str);
                        byte[] imagebyte = GetImageBytesFromOLEField(b); //Error caught here

                        MemoryStream ms = new MemoryStream();
                        ms.Write(imagebyte, 0, imagebyte.Length);
                    }    
                }

可以找到方法GetImageBytesFromOLEField here。它给我的错误是关于字符串的索引长度strVTemp = strTemp.Substring（0,300）;

同样，这里的主要问题是如何将 DataRow行[“FOTO”] 中的 OLE Object 转换为 byte [] 然后用在那个方法中。

Answer 1

这里的问题是嵌入的图片不是简单的BMP或JPEG。这是一个

Microsoft Word Picture

并且OLE头信息比原始GetImageBytesFromOLEField()代码的300字节窗口大得多。（也就是说，在扫描300个字节后，它只是放弃了“无法确定标题大小......”。）

以下是该类代码的更新版本。粗略测试包括提供的Microsoft Word Picture，简单的BMP和简单的JPEG。

using System;
using System.Collections.Generic;
using System.Linq;

namespace OleImageTest
{
    public static class OleImageUnwrap
    {
        public static byte[] GetImageBytesFromOLEField(byte[] oleFieldBytes)
        {
            // adapted from http://blogs.msdn.com/b/pranab/archive/2008/07/15/removing-ole-header-from-images-stored-in-ms-access-db-as-ole-object.aspx

            const int maxNumberOfBytesToSearch = 10000;
            byte[] imageBytes;  // return value

            var imageSignatures = new List<byte[]>();
            // PNG_ID_BLOCK = "\x89PNG\r\n\x1a\n"
            imageSignatures.Add(new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A });
            // JPG_ID_BLOCK = "\xFF\xD8\xFF"
            imageSignatures.Add(new byte[] { 0xFF, 0xD8, 0xFF });
            // GIF_ID_BLOCK = "GIF8"
            imageSignatures.Add(new byte[] { 0x47, 0x49, 0x46, 0x38 });
            // TIFF_ID_BLOCK = "II*\x00"
            imageSignatures.Add(new byte[] { 0x49, 0x49, 0x2A, 0x00 });
            // BITMAP_ID_BLOCK = "BM"
            imageSignatures.Add(new byte[] { 0x42, 0x4D });

            int numberOfBytesToSearch = (oleFieldBytes.Count() < maxNumberOfBytesToSearch ? oleFieldBytes.Count() : maxNumberOfBytesToSearch);
            var startingBytes = new byte[numberOfBytesToSearch];
            Array.Copy(oleFieldBytes, startingBytes, numberOfBytesToSearch);

            var positions = new List<int>();
            foreach (byte[] blockSignature in imageSignatures)
            {
                positions = startingBytes.IndexOfSequence(blockSignature, 0);
                if (positions.Count > 0)
                {
                    break;
                }
            }
            int iPos = -1;
            if (positions.Count > 0)
            {
                iPos = positions[0];
            }

            if (iPos == -1)
                throw new Exception("Unable to determine header size for the OLE Object");

            imageBytes = new byte[oleFieldBytes.LongLength - iPos];
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            ms.Write(oleFieldBytes, iPos, oleFieldBytes.Length - iPos);
            imageBytes = ms.ToArray();
            ms.Close();
            ms.Dispose();
            return imageBytes;
        }

        private static List<int> IndexOfSequence(this byte[] buffer, byte[] pattern, int startIndex)
        {
            // ref: http://stackoverflow.com/a/332667/2144390
            List<int> positions = new List<int>();
            int i = Array.IndexOf<byte>(buffer, pattern[0], startIndex);
            while (i >= 0 && i <= buffer.Length - pattern.Length)
            {
                byte[] segment = new byte[pattern.Length];
                Buffer.BlockCopy(buffer, i, segment, 0, pattern.Length);
                if (segment.SequenceEqual<byte>(pattern))
                    positions.Add(i);
                i = Array.IndexOf<byte>(buffer, pattern[0], i + 1);
            }
            return positions;
        }
    }
}

在C＃中将Access图像OLE对象转换为原始图像字节数组

1 个答案: