Get a Header Attribute of a Related Item

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Demonstrates the Chilkat Email.GetRelatedAttr method, which returns a header-field attribute value from a header field of the Nth related item. The first argument is the zero-based related-item index, the second names a header field, and the third names an attribute within it. This example loads an image from a file into a BinData object, adds it as a related item with AddRelatedBd (capturing the generated Content-ID and referencing it from the HTML), then reads the name attribute of the related item's Content-Type header.

Background: Related items (inline images, style sheets) are MIME parts whose headers may carry named parameters — for instance Content-Type: image/png; name="logo.png". Because an image is binary, it is loaded into a BinData object (here from a file) and added with AddRelatedBd, rather than being treated as text. GetRelatedAttr then extracts one named attribute from a chosen header of a specific related part, the related-item analogue of GetAttachmentAttr, so you don't have to parse the raw header yourself.

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bool success = false;

//  Demonstrates the GetRelatedAttr method, which returns a header-field attribute value
//  from a header field of the Nth related item.  The first argument is the zero-based related-item
//  index, the second is the header field name, and the third is the attribute name.

Chilkat.Email email = new Chilkat.Email();
email.Subject = "GetRelatedAttr example";

//  Load the image data from a file into a BinData object.
Chilkat.BinData bdImage = new Chilkat.BinData();
success = bdImage.LoadFile("qa_data/images/logo.png");
if (success == false) {
    Debug.WriteLine(bdImage.LastErrorText);
    return;
}

//  Add the image as a related item from the BinData; capture its generated Content-ID.
string cid = email.AddRelatedBd("logo.png",bdImage);
if (email.LastMethodSuccess == false) {
    Debug.WriteLine(email.LastErrorText);
    return;
}

//  Reference the related item in the HTML body by its Content-ID.
Chilkat.StringBuilder sbHtml = new Chilkat.StringBuilder();
sbHtml.Append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>");
int numReplaced = sbHtml.Replace("PLACEHOLDER_CID",cid);
email.SetHtmlBody(sbHtml.GetAsString());

//  Get the "name" attribute of the related item's Content-Type header (index 0).
string val = email.GetRelatedAttr(0,"Content-Type","name");
Debug.WriteLine("Related item Content-Type name attribute: " + val);

//  Note: The path "qa_data/images/logo.png" is a relative local filesystem path,
//  relative to the current working directory of the running application.