Unable to cast object of type 'system.string' to type 'system.Byte[]' when trying to download a file from database - asp.net

Question

I am trying to download a file from database but its giving me an error called Unable to cast object of type 'System.String' to type 'System.Byte[]' on the line : Response.AddHeader("Content-Length", bytes.ToString());
Please tell me how can I cast string to byte in my case, thank you in advance.
I have a column named SaleFileName from which I want to download a file.
Aspx code:
<asp:TemplateField HeaderText="RecieptName" SortExpression="RecieptName">
<ItemTemplate>
<asp:LinkButton ID="LinkButton1" runat="server" CommandName="Download" CommandArgument='<%# Bind("SaleName") %>' Text='<%# Bind("SaleName") %>' ></asp:LinkButton>
</ItemTemplate>
</asp:TemplateField>
Code Behind File:
protected void gridContributions_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "Download")
{
// make sure fileName contains only file name like 'test.pdf'
string FileName = Convert.ToString(e.CommandArgument);
// make sure filePath contains file path like 'Uploads/Scheme/test.pdf'
string FilePath = e.CommandArgument.ToString();
string connectionString = WebConfigurationManager.ConnectionStrings["ConnectionString2"].ConnectionString;
// SqlConnection con = new SqlConnection(connectionString);
// byte[] bytes;
//string ContentType;
using (SqlConnection con = new SqlConnection(connectionString))
{
using (SqlCommand cmd = new SqlCommand())
{
cmd.CommandText = "selectSaleFileName from Contributions where SaleFileName = #SaleFileName";
cmd.Parameters.AddWithValue("#SaleFileName", FileName);
//d.CommandType = CommandType.StoredProcedure;
cmd.Connection = con;
con.Open();
using ( SqlDataReader sdr = cmd.ExecuteReader())
{
sdr.Read();
bytes = (byte[])sdr["SaleFileName"];
//byte data = System.Text.Encoding.Unicode.GetBytes(SaleFileName.ToString);
}
con.Close();
}
}
Response.Clear();
Response.Buffer = true;
// Read the original file from disk
FileStream myFileStream = new FileStream( FilePath ,FileMode.Open);
long FileSize = myFileStream.Length;
byte[] Buffer = new byte[Convert.ToInt32(FileSize)];
myFileStream.Read(Buffer, 0, Convert.ToInt32(FileSize));
myFileStream.Close();
// // Tell the browse stuff about the file
Response.AddHeader("Content-Length", bytes.ToString());
// Response.AddHeader("Content-Length", FileNam
//Response.AddHeader("Content-Disposition", "inline; filename=" & fileName.Replace(" ", "_"));
Response.AddHeader("Content-Disposition", "attachment; FileName=" + FileName + ";");
Response.TransmitFile(FileName);
Response.ContentType = "application/octet-stream";
// Send the data to the browser
Response.BinaryWrite(Buffer);
Response.End();
}
}

Answer 1

You can't cast byte[] to string (unless its textual data and you should encode the data using any encoding like unicode, ASCII)
anyway, the problem in the Content-Length on http header, it should be the length of the file
so replace this line:
Response.AddHeader("Content-Length", bytes.ToString());
with this:
Response.AddHeader("Content-Length", FileSize.ToString());
if the file is stored databaase you need to get it as byte array, the following code will help you:
private byte[] ReadFileFromDatabase(string FileName) {
string connectionString = WebConfigurationManager.ConnectionStrings["ConnectionString2"].ConnectionString;
byte[] bytes = null;
using (SqlConnection con = new SqlConnection(connectionString))
{
using (SqlCommand cmd = new SqlCommand())
{
cmd.CommandText = "selectSaleFileName from Contributions where SaleFileName = #SaleFileName";
cmd.Parameters.AddWithValue("#SaleFileName", FileName);
cmd.Connection = con;
con.Open();
using ( SqlDataReader sdr = cmd.ExecuteReader())
{
if (sdr.Read() )
bytes = (byte[])sdr["SaleFileName"];
}
con.Close();
}
}
return bytes;
}
protected void gridContributions_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "Download")
{
string FileName = Convert.ToString(e.CommandArgument);
byte[] bytes = ReadFileFromDatabase(FileName);
Response.Clear()
Response.ContentType = "application/octet-stream"
Response.AddHeader("Content-Disposition", "attachment; FileName=" + FileName + ";");
Response.BinaryWrite(bytes)
Response.End()
}
}
if your file is stored outside database:
public static void DownloadFile(string path, string contentType)
{
FileInfo file = new FileInfo(path);
if (file.Exists)
{
Response.Clear();
Response.ClearHeaders();
Response.ClearContent();
Response.AddHeader("Content-Type", contentType);
Response.AddHeader("Content-Disposition", "attachment; filename=" + file.Name);
Response.AddHeader("Content-Length", file.Length.ToString());
Response.Flush();
Response.TransmitFile(file.FullName);
Response.End();
}
}
call it as:
string fullPath = Server.MapPath(relativePath);
DownloadFile(fullPath , "application/octet-stream");