Dart

Convert a MIME Entity to multipart/alternative

Demonstrates the Chilkat Mime.ConvertToMultipartAlt method, which wraps the current entity in a new outer multipart/alternative, making the original the first child. It takes no arguments.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: Use this to add an alternate rendering to an existing message — for example, promoting a plain-text message so an HTML version can be added alongside it. The original content becomes the first (least-preferred) alternative, and you append the richer representation after it. As with the mixed conversion, message-level headers move to the new outer entity.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  final mime = CkMime();
  try {
    mime.loadMimeFile('qa_data/message.eml');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Wrap the current entity in a new outer multipart/alternative entity.  The original entity
  // becomes the first child, ready for an alternate representation to be added.
  try {
    mime.convertToMultipartAlt();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Add an alternative representation of the same content.
  final htmlPart = CkMime();
  try {
    htmlPart.setBodyFromHtml('<html><body>HTML alternative.</body></html>');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    mime.appendPart(htmlPart);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Number of parts: ${mime.numParts}');
}