React Native

Get a Header Attribute of a Related Item

Demonstrates the Chilkat Email.GetRelatedAttr method, which returns a header-field attribute value from a header field of the Nth related item. The first argument is the zero-based related-item index, the second names a header field, and the third names an attribute within it. 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 the name attribute of the related item's Content-Type header.

Background: Related items (inline images, style sheets) are MIME parts whose headers may carry named parameters — for instance Content-Type: image/png; name="logo.png". Because an image is binary, it is loaded into a BinData object (here from a file) and added with AddRelatedBd, rather than being treated as text. GetRelatedAttr then extracts one named attribute from a chosen header of a specific related part, the related-item analogue of GetAttachmentAttr, so you don't have to parse the raw header yourself.

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import { BinData, Email, StringBuilder } from '@chilkat/react-native'

function chilkatExample() {
  // Demonstrates the GetRelatedAttr method, which returns a header-field attribute value
  // from a header field of the Nth related item.  The first argument is the zero-based related-item
  // index, the second is the header field name, and the third is the attribute name.

  const email = new Email();
  email.subject = 'GetRelatedAttr example';

  // Load the image data from a file into a BinData object.
  const bdImage = new BinData();
  try {
    bdImage.loadFile('qa_data/images/logo.png');
  } catch {
    console.log(bdImage.lastErrorText);
    return;
  }

  // Add the image as a related item from the BinData; capture its generated Content-ID.
  let cid: string;
  try {
    cid = email.addRelatedBd('logo.png', bdImage);
  } catch {
    console.log(email.lastErrorText);
    return;
  }

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

  // Get the "name" attribute of the related item's Content-Type header (index 0).
  const val = email.getRelatedAttr(0, 'Content-Type', 'name');
  console.log(`Related item Content-Type name attribute: ${val}`);

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