Objective-C

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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Objective-C

#import <CkoEmail.h>
#import <NSString.h>
#import <CkoStringBuilder.h>

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

CkoEmail *email = [[CkoEmail alloc] init];
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.
NSString *cid = [email AddRelatedString: @"styles.css" str: @"body { color: black; }" charset: @"utf-8"];
if (email.LastMethodSuccess == NO) {
    NSLog(@"%@",email.LastErrorText);
    return true;
}

//  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.
CkoStringBuilder *sbHtml = [[CkoStringBuilder alloc] init];
[sbHtml Append: @"<html><head><link rel=\"stylesheet\" href=\"cid:PLACEHOLDER_CID\"/></head><body>Styled content.</body></html>"];
int numReplaced = [[sbHtml Replace: @"PLACEHOLDER_CID" replacement: cid] intValue];
[email SetHtmlBody: [sbHtml GetAsString]];

//  Add a custom header field to the first related item (index 0).
[email AddRelatedHeader: [NSNumber numberWithInt: 0] fieldName: @"X-Custom-Related-Header" fieldValue: @"some value"];

//  The custom header now appears in the related item's MIME part.
NSLog(@"%@",[email GetMime]);