Firebase下Android与iOS通知兼容：全状态自定义处理方案咨询

核心矛盾 #

iOS端需要通知payload包含notification字段（可空），才能保证应用在活跃、后台、终止状态下都能触发自定义处理逻辑；而Android端恰好相反，不能携带notification字段，只能保留data字段——否则应用在后台或终止状态时，系统会直接接管通知展示，无法执行下载图片这类自定义操作。

解决方案思路 #

通过后端区分设备类型下发不同payload + 客户端各自针对性处理，实现双端全状态下的通知自定义展示。

1. 后端payload适配

• iOS设备：下发包含notification字段（填充基础通知内容）+ data字段（存储自定义业务数据）的payload，同时必须开启APNS的mutable-content参数，允许iOS修改通知内容。
• Android设备：仅下发data字段，把通知展示内容（标题、正文）和自定义数据都放在data中。

示例Payload

iOS：

{
  "notification": {
    "title": "新消息提醒",
    "body": "您有一条未读消息"
  },
  "data": {
    "custom_id": "12345",
    "image_url": "https://example.com/avatar.jpg"
  },
  "apns": {
    "payload": {
      "aps": {
        "mutable-content": 1
      }
    }
  }
}

Android：

{
  "data": {
    "title": "新消息提醒",
    "body": "您有一条未读消息",
    "custom_id": "12345",
    "image_url": "https://example.com/avatar.jpg"
  }
}

2. 客户端自定义处理

Android端（基于onMessageReceived）

当payload仅包含data字段时，无论应用处于活跃、后台还是终止状态，都会触发onMessageReceived方法。我们可以在这里完成所有自定义操作，再手动构建并展示通知：

override fun onMessageReceived(message: RemoteMessage) {
    super.onMessageReceived(message)
    // 从data中提取所有数据
    val title = message.data["title"] ?: ""
    val body = message.data["body"] ?: ""
    val imageUrl = message.data["image_url"]
    val customId = message.data["custom_id"]

    // 执行自定义操作，比如下载图片
    imageUrl?.let { url ->
        downloadRemoteImage(url) { bitmap ->
            buildAndShowNotification(title, body, bitmap, customId)
        }
    } ?: run {
        buildAndShowNotification(title, body, null, customId)
    }
}

private fun buildAndShowNotification(title: String, body: String, bitmap: Bitmap?, customId: String?) {
    // 创建通知渠道（Android 8.0+必填）
    val channelId = "custom_notification_channel"
    val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        val channel = NotificationChannel(channelId, "自定义通知", NotificationManager.IMPORTANCE_DEFAULT)
        notificationManager.createNotificationChannel(channel)
    }

    // 构建通知
    val builder = NotificationCompat.Builder(this, channelId)
        .setSmallIcon(R.drawable.ic_notify)
        .setContentTitle(title)
        .setContentText(body)
        .setPriority(NotificationCompat.PRIORITY_DEFAULT)
    
    // 添加大图样式（如果有下载好的图片）
    bitmap?.let {
        builder.setLargeIcon(it)
        builder.setStyle(NotificationCompat.BigPictureStyle().bigPicture(it))
    }

    // 发送通知
    notificationManager.notify(System.currentTimeMillis().toInt(), builder.build())
}

// 简化的图片下载方法
private fun downloadRemoteImage(url: String, callback: (Bitmap?) -> Unit) {
    Thread {
        val bitmap = try {
            val inputStream = URL(url).openStream()
            BitmapFactory.decodeStream(inputStream)
        } catch (e: Exception) {
            null
        }
        runOnUiThread { callback(bitmap) }
    }.start()
}

iOS端（基于didReceive(_:withContentHandler:)）

因为payload携带了notification字段且开启了mutable-content，应用在所有状态下都会触发该方法。我们可以在这里下载图片、修改通知内容，最后将处理后的内容返回给系统：

func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
    let userInfo = request.content.userInfo
    let imageUrlString = userInfo["image_url"] as? String
    guard let mutableContent = request.content.mutableCopy() as? UNMutableNotificationContent else {
        contentHandler(request.content)
        return
    }

    // 没有图片直接返回原内容
    guard let imageUrl = URL(string: imageUrlString ?? "") else {
        contentHandler(mutableContent)
        return
    }

    // 异步下载图片并添加为通知附件
    URLSession.shared.dataTask(with: imageUrl) { data, _, error in
        guard let data = data, let image = UIImage(data: data), error == nil else {
            contentHandler(mutableContent)
            return
        }

        // 将图片保存到临时目录
        let tempDir = FileManager.default.temporaryDirectory
        let imageFileName = UUID().uuidString + ".jpg"
        let imageFileUrl = tempDir.appendingPathComponent(imageFileName)
        
        do {
            try image.jpegData(compressionQuality: 0.8)?.write(to: imageFileUrl)
            let attachment = try UNNotificationAttachment(identifier: "notification_image", url: imageFileUrl, options: nil)
            mutableContent.attachments = [attachment]
            contentHandler(mutableContent)
        } catch {
            contentHandler(mutableContent)
        }
    }.resume()
}

内容的提问来源于stack exchange，提问作者Lukas