Dart

Add a Related File to an HTML Email

Demonstrates the Chilkat Email.AddRelatedFile method, which adds the contents of a local file as a related MIME resource and returns the generated Content-ID. The returned value is the bare Content-ID — no angle brackets and no cid: prefix — so if it returns CID-123@example, the HTML reference is cid:CID-123@example. Because the Content-ID is generated by the call, this example adds the image first, then builds the HTML body in a StringBuilder — using a placeholder in the <img> tag that is replaced with the returned Content-ID — and passes the result to SetHtmlBody.

Background: To embed an image so it displays inside an HTML email (rather than being downloaded from a web server), you add it as a "related" part and reference it from the HTML with a cid: URL that matches the part's Content-ID. Since Chilkat assigns that ID when you add the file, the natural order is: add the related file, capture the returned ID, then build the <img src="cid:..."> reference from it. A StringBuilder makes assembling and updating the HTML convenient.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates the AddRelatedFile method, which adds a local file as a related MIME
  // resource (such as an image displayed by an HTML body) and returns the generated
  // Content-ID.  The HTML references the item using cid:<Content-ID>.

  final email = CkEmail();
  email.subject = 'Email with a related image';

  // Add the image file as a related item first.  The return value is the bare Content-ID
  // (no angle brackets and no "cid:" prefix).
  final String cid;
  try {
    cid = email.addRelatedFile('qa_data/images/logo.png');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Build the HTML body in a StringBuilder, using a placeholder where the image's
  // Content-ID will go.
  final sbHtml = CkStringBuilder();
  sbHtml.append('<html><body><img src="cid:PLACEHOLDER_CID"/></body></html>');

  // Replace the placeholder with the actual Content-ID returned by AddRelatedFile.
  final numReplaced = sbHtml.replace('PLACEHOLDER_CID', cid);

  // Set the HTML body from the StringBuilder result.
  email.setHtmlBody(sbHtml.getAsString());

  print('Related Content-ID = $cid');
  print('NumRelatedItems = ${email.numRelatedItems}');

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