Get the Content-ID of a Related Item

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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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    success := false

    //  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.

    email := chilkat.NewEmail()
    email.SetSubject("GetRelatedContentID example")

    //  Load the image data from a file into a BinData object.
    bdImage := chilkat.NewBinData()
    success = bdImage.LoadFile("qa_data/images/logo.png")
    if success == false {
        fmt.Println(bdImage.LastErrorText())
        email.DisposeEmail()
        bdImage.DisposeBinData()
        return
    }

    //  Add the image as a related item from the BinData; capture its generated Content-ID.
    cid := email.AddRelatedBd("logo.png",bdImage)
    if email.LastMethodSuccess() == false {
        fmt.Println(email.LastErrorText())
        email.DisposeEmail()
        bdImage.DisposeBinData()
        return
    }

    //  Reference the related item in the HTML body by its Content-ID.
    sbHtml := chilkat.NewStringBuilder()
    sbHtml.Append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>")
    numReplaced := sbHtml.Replace("PLACEHOLDER_CID",*cid)
    email.SetHtmlBody(*sbHtml.GetAsString())

    //  Read the Content-ID of the first related item (index 0).
    cid0 := email.GetRelatedContentID(0)
    fmt.Println("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.

    email.DisposeEmail()
    bdImage.DisposeBinData()
    sbHtml.DisposeStringBuilder()