Dart

Get a Header Field from an Alternative Body

Demonstrates the Chilkat Email.GetAltHeaderField method, which returns the value of a header field within the Nth alternative body's MIME sub-part. The first argument is the zero-based alternative index; the second is the header field name. This example builds a message with plain-text and HTML alternatives and reads the Content-Type of the first alternative.

Background: A multipart/alternative message is a tree: each alternative body is its own MIME sub-part with its own little header block (Content-Type, Content-Transfer-Encoding, etc.). The top-level Email header methods read the message headers, whereas GetAltHeaderField reaches into a specific alternative's sub-part — useful for inspecting exactly how each representation is typed and encoded.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates the GetAltHeaderField method, which returns the value of a header field
  // within the Nth alternative body's MIME sub-part.  The 1st argument is the zero-based
  // alternative index; the 2nd is the header field name.

  final email = CkEmail();

  // Create an email with plain-text and HTML alternatives.
  email.setTextBody('This is the plain-text alternative.', 'text/plain');
  email.addHtmlAlternativeBody('<html><body>This is the HTML alternative.</body></html>');

  // Get the Content-Type header of the first alternative body (index 0).
  final ct = email.getAltHeaderField(0, 'Content-Type');
  print('Alternative 0 Content-Type: $ct');
}