Dart

Get the Content-ID of a Related Item

Demonstrates the Chilkat Email.GetRelatedContentID method, which returns the Content-ID of a related item (typically an image or style sheet embedded within an HTML email). The index is zero-based. 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 that Content-ID back.

Background: The Content-ID is the anchor that ties an inline resource to the HTML that displays it: the body references cid: plus the ID, and the matching related part carries that same Content-ID. Because an image is binary, it is loaded into a BinData object (here from a file) and added with AddRelatedBd. Reading the Content-ID back lets a program verify or rewrite those links — for example when relocating embedded images or converting a message for display outside a mail client.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates the GetRelatedContentID method, which returns the Content-ID of a related
  // item.  Related items are typically images and style sheets embedded within HTML emails.
  // The index is zero-based.

  final email = CkEmail();
  email.subject = 'GetRelatedContentID example';

  // Load the image data from a file into a BinData object.
  final bdImage = CkBinData();
  try {
    bdImage.loadFile('qa_data/images/logo.png');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Add the image as a related item from the BinData; capture its generated Content-ID.
  final String cid;
  try {
    cid = email.addRelatedBd('logo.png', bdImage);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Reference the related item in the HTML body by its Content-ID.
  final sbHtml = CkStringBuilder();
  sbHtml.append('<html><body><img src="cid:PLACEHOLDER_CID"/></body></html>');
  final numReplaced = sbHtml.replace('PLACEHOLDER_CID', cid);
  email.setHtmlBody(sbHtml.getAsString());

  // Read the Content-ID of the first related item (index 0).
  final cid0 = email.getRelatedContentID(0);
  print('Related item 0 Content-ID: $cid0');

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