Attach an array of doubles to a mail in Swift

Question

I am trying to attach an array of doubles to a mail using the MFMailComposeViewController class. So far this is my code in the ViewController class:

func prepareMail(data:[Double]) {                
        // Compose the mail
        let mailComposer = MFMailComposeViewController()
        mailComposer.mailComposeDelegate = self
        mailComposer.setToRecipients(["mail@mail.com"])
        mailComposer.setSubject("subject")
        mailComposer.setMessageBody("Hello ", isHTML: false)

        // Name data files (accelerometer + label)
        let fileName = "file"

        if let dataToAttach = data {
            //Attach File
            mailComposer.addAttachmentData(dataToAttach, mimeType: "text/plain", fileName: "\(fileName)")
            self.present(mailComposer, animated: true, completion: nil)
        }
    }
}

This code raises the following message:

initializer for conditional binding must have Optional type, not [Double]

So here are my thoughts:

• Option 1: Convert the array of doubles to a string and send it as a plain/text file. My intuition, however, tells me that this is not a nice solution. I am not a fan of parsing.
• Option 2: Encode the array somehow and send it using another mimetype other than plain/text. I explored some options in IANA mime Types, but I am not familiar at all and do not know where to start with.

I am not sure how to proceed.

Answer 1

Your problem is this line if let dataToAttach = data because your data is [Double] and can't be nil, so you don't need to check of is nil, or you can change the parameters type to [Double]? to avoid this compiler error.

Replacing this:

if let dataToAttach = data {
            //Attach File
            mailComposer.addAttachmentData(dataToAttach, mimeType: "text/plain", fileName: "\(fileNames[i])")
            self.present(mailComposer, animated: true, completion: nil)
        }

by this:

   func prepareMail(data:[Double]) {
    // Compose the mail
    let mailComposer = MFMailComposeViewController()
    mailComposer.mailComposeDelegate = self
    mailComposer.setToRecipients(["mail@mail.com"])
    mailComposer.setSubject("subject")
    mailComposer.setMessageBody("Hello ", isHTML: false)

    // Name data files (accelerometer + label)
    let fileName = "file"

    if let dataToAttach = data.map({String($0)}).joined(separator: "\n").data(using: .utf8)
    {
        mailComposer.addAttachmentData(dataToAttach, mimeType: "text/plain", fileName: "\(fileNames[i])")
        self.present(mailComposer, animated: true, completion: nil)
    }

}

will be enough.