payload：-

{
 "notification": {
     "title": "New image",
     "body": "Check out this cool image!"
 },
 "data": {
     "title": "Example Notification001",
     "body": "Check out this cool image!:slightly_smiling_face:",
     "click_action": "FLUTTER_NOTIFICATION_CLICK",
     "image": "https://img.freepik.com/free-photo/chicken-wings-barbecue-sweetly-sour-sauce-picnic-summer-menu-tasty-food-top-view-flat-lay_2829-6471.jpg"
 },
 "apns": {
     "payload": {
         "aps": {
             "mutable-content": 1,
             "sound": "Default"
         }
     }
 },
 "registrationToken": [
     "**Your fcm token**"
 ]
}

创建通知服务扩展

成功创建iOS应用程序后，您需要创建通知服务扩展。以下是如何创建通知服务扩展的步骤。
1.在Xcode菜单中，转到File > New > Target。
1.选择Notification Service Extension。
1.给出扩展服务的名称并单击完成按钮。

根据您的意愿键入产品名称（例如：-ImageNotificationService）
您在xcode中添加了firebase Messaging包（此行是在您的包中安装firebase messaging）（target 'this your notification service contact name'）

target 'ImageNotificationService' do
  use_frameworks!
  pod 'Firebase/Messaging'
end

此Info.plist在imagenotificationservice文件夹plist中

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>NSExtension</key>
    <dict>
        <key>UNNotificationExtensionCategory</key>
        <string>imageNotificationCategory</string>
        <key>NSExtensionAttributes</key>
        <dict>
            <key>UNNotificationExtensionDefaultContentHidden</key>
            <false/>
            <key>UNNotificationExtensionInitialContentSizeRatio</key>
            <real>1</real>
        </dict>
        <key>NSExtensionPointIdentifier</key>
        <string>com.apple.usernotifications.service</string>
        <key>NSExtensionPrincipalClass</key>
        <string>$(PRODUCT_MODULE_NAME).NotificationService</string>
    </dict>
</dict>
</plist>

此行为notificationservice.swift

import UIKit
import UserNotifications
import FirebaseMessaging

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)
        guard let bestAttemptContent = bestAttemptContent else { return }
        // Modify the notification content here as you wish
        let data = bestAttemptContent.userInfo as NSDictionary
        let pref = UserDefaults.init(suiteName: "group.id.gits.notifserviceextension")
        pref?.set(data, forKey: "NOTIF_DATA")
        pref?.synchronize()
        NSLog("notificationserviceExtension")
        guard let attachmentURL = data["image"] as? String else {
                    contentHandler(bestAttemptContent)
                    return
                }
        do {
             print("unNotification sucesss01---\(attachmentURL)")
            let imageData = try Data(contentsOf: URL(string: attachmentURL)!)
            guard let attachment = UNNotificationAttachment.create(imageFileIdentifier: "image.jpg", data: imageData, options: nil) else {
                contentHandler(bestAttemptContent)
                return
            }
            bestAttemptContent.attachments = [attachment]
            contentHandler(bestAttemptContent.copy() as! UNNotificationContent)
            
        } catch {
            self.bestAttemptContent?.title = "\(self.bestAttemptContent?.title ?? "")."
            self.bestAttemptContent?.body = "\(self.bestAttemptContent?.body ?? "")"
            contentHandler(bestAttemptContent)
            print("Unable to load data: \(error)")

        }
    }
    
    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)
        }
    }

}
extension UNNotificationAttachment {
    static func create(imageFileIdentifier: String, data: Data, options: [NSObject: AnyObject]?) -> UNNotificationAttachment? {
        let fileManager = FileManager.default
        let tmpSubFolderName = ProcessInfo.processInfo.globallyUniqueString
        let tmpSubFolderURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(tmpSubFolderName, isDirectory: true)

        do {
            try fileManager.createDirectory(at: tmpSubFolderURL, withIntermediateDirectories: true, attributes: nil)
            let fileURL = tmpSubFolderURL.appendingPathComponent(imageFileIdentifier)
            try data.write(to: fileURL)
            let attachment = try UNNotificationAttachment(identifier: imageFileIdentifier, url: fileURL, options: options)
            return attachment
        } catch {
            print("Error creating attachment: \(error)")
        }
        return nil
    }
}

如果您有任何疑问，请在下面评论：-