App Extension: Notification Service

NotificationServiceDemo.swift

import UserNotifications
import MobileCoreServices

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 {
            // Modify the notification content here...
            // bestAttemptContent.title = "[modified] \(bestAttemptContent.title)"
            tryToFetchAttachment(attemptContent: bestAttemptContent, contentHandler: contentHandler)
        }
    }
    
    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 {
            // Modify the notification content here...
            tryToFetchAttachment(attemptContent: bestAttemptContent, contentHandler: contentHandler) // 如果两次都失败，该通知最终还是会显示的，只是没有 attachment 罢了。
        }
    }

    // 消息体顶层填入 image 参数及其指向的图片 url（若不用 https，需在 info.plist 里设置 Allow Arbitrary Loads 为 YES）
    private func tryToFetchAttachment(attemptContent: UNMutableNotificationContent, contentHandler: @escaping (UNNotificationContent) -> Void) {
        // Modify the notification content here...
        guard let s = attemptContent.userInfo[AnyHashable("image")] as? String, let imageURL = URL(string: s) else {
            contentHandler(attemptContent)
            return
        }
        URLSession.shared.downloadTask(with: imageURL, completionHandler: { (url, response, error) in
            guard error == nil, let fileURL = url else {
                return
            }
            guard let attachment = try? UNNotificationAttachment(identifier: response?.suggestedFilename ?? "image.jpeg", file: FileObject.cacheURL(fileURL), options: nil) else {
                return
            }
            attemptContent.attachments = [attachment]
            contentHandler(attemptContent)
        }).resume()
    }
}


enum FileObject {
    case data(Data)
    case cacheURL(URL)
}

extension UNNotificationAttachment {

    /// Save the image to disk, or move cache file to tmp file
    convenience init(identifier: String, file: FileObject, options: [AnyHashable : Any]?) throws {
        let attachSubFolderName = ProcessInfo.processInfo.globallyUniqueString
        let attachSubFolderURL = URL.init(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(attachSubFolderName, isDirectory: true)
        let attachFileURL = attachSubFolderURL.appendingPathComponent(identifier)

        try FileManager.default.createDirectory(at: attachSubFolderURL, withIntermediateDirectories: true, attributes: nil)

        switch file {
        case .cacheURL(let cacheFileURL):   // 转移
            try FileManager.default.copyItem(at: cacheFileURL, to: attachFileURL)

        case .data(let data):               // 保存为文件
            try data.write(to: attachFileURL, options: [])
        }

        try self.init(identifier: identifier, url: attachFileURL, options: options)
    }
}