Swift 3: implement a service extension and download an image attachment.

Swift 3: How to implement a service extension.swift

//
//  NotificationService.swift
//  Service
//
//  Created by Barbara Rodeker on 28/09/16.
//  Copyright © 2016 Barbara Rodeker. All rights reserved.
//

import UserNotifications

class NotificationService: UNNotificationServiceExtension {

    var contentHandler: ((UNNotificationContent) -> Void)?
    var bestAttemptContent: UNMutableNotificationContent?

    override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        self.contentHandler = contentHandler
        bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
        
        if let bestAttemptContent = bestAttemptContent {

            if let urlString = bestAttemptContent.userInfo["picture"] as? String,
                 let data = NSData(contentsOf: URL(string:urlString)!) as? Data {
                let path = NSTemporaryDirectory() + "attachment"
                _ = FileManager.default.createFile(atPath: path, contents: data, attributes: nil)
                
                do {
                    let file = URL(fileURLWithPath: path)
                    let attachment = try UNNotificationAttachment(identifier: "attachment", url: file,options:[UNNotificationAttachmentOptionsTypeHintKey : "public.jpeg"])
                    bestAttemptContent.attachments = [attachment]
                    
                } catch {
                    print(error)
                    
                }
            }
            contentHandler(bestAttemptContent)
        }
    }
    
    override func serviceExtensionTimeWillExpire() {
        // Called just before the extension will be terminated by the system.
        // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
        if let contentHandler = contentHandler, let bestAttemptContent =  bestAttemptContent {
            contentHandler(bestAttemptContent)
        }
    }

}

// The example is based in a payload like the following:
/*{
	"aps":{
		"alert":"Do you like puppies?",
		"category":"any-name-2",
		"mutable-content":1
	},
	"picture" : "https://pixabay.com/static/uploads/photo/2015/02/05/12/09/chihuahua-624924__180.jpg"
	
}*/