VB.NET

Add a Custom Header to a Related Item

Demonstrates the Chilkat Email.AddRelatedHeader method, which adds a custom MIME header field to an existing related item identified by its zero-based index. This example first adds a related style sheet (which becomes index 0) and captures its generated Content-ID, builds an HTML body that references the style sheet by that cid:, then attaches an extra header field to the related item and prints the resulting MIME.

Background: Like attachments, each related item (an inline image, style sheet, etc.) is a MIME part with its own small header block describing that part — Content-Type, Content-ID, Content-Location, and so on. AddRelatedHeader lets you insert additional fields into that per-part block, which is occasionally required for interoperability with clients that look for specific custom headers on embedded resources.

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VB.NET

'  Demonstrates the AddRelatedHeader method, which adds a custom MIME header field to an
'  existing related item, identified by its zero-based index.

Dim email As New Chilkat.Email
email.Subject = "Related item with a custom header"

'  Add a related item first (a style sheet); capture its generated Content-ID.  It becomes
'  related-item index 0.
Dim cid As String = email.AddRelatedString("styles.css","body { color: black; }","utf-8")
If (email.LastMethodSuccess = False) Then
    Debug.WriteLine(email.LastErrorText)
    Exit Sub
End If


'  Build the HTML body, referencing the related style sheet by its Content-ID.  A
'  placeholder is used and then replaced with the actual Content-ID.
Dim sbHtml As New Chilkat.StringBuilder
sbHtml.Append("<html><head><link rel=""stylesheet"" href=""cid:PLACEHOLDER_CID""/></head><body>Styled content.</body></html>")
Dim numReplaced As Integer = sbHtml.Replace("PLACEHOLDER_CID",cid)
email.SetHtmlBody(sbHtml.GetAsString())

'  Add a custom header field to the first related item (index 0).
email.AddRelatedHeader(0,"X-Custom-Related-Header","some value")

'  The custom header now appears in the related item's MIME part.
Debug.WriteLine(email.GetMime())