Flutter图片通知后台及终止状态失效问题求助

问题现象 #

iOS平台下，Flutter应用前台运行时图片通知正常展示，但后台或应用终止状态下，图片无法正常显示。当前已实现将图片下载至Directory.systemTemp临时目录并在前台展示的逻辑。

现有实现代码 #

图片下载逻辑 #

if (Platform.isIOS) {
    if (message.data['image'] != null) {
      url = message.data['image'];
      var formatname = url.toString().split(".");
      var length = formatname.length - 1;
      var format = formatname[length];
      log("message$format");
      var formatlist = ['jpg', 'gif', 'png'];
      bigpicture = await DownloadUtil.downloadfiles(url,
          "bigpicture.${(format.isEmpty || formatlist.contains(format)) ? format : "jpg"}");
      print(bigpicture);
    } else {
      bigpicture = " ";
    }
  } 

通知展示代码 #

flutterLocalNotificationsPlugin.show(
        id,
        message.data["title"],
        message.data["body"],
        NotificationDetails(
          iOS: ios != null
              ? IOSNotificationDetails(
                  attachments: message.data['image'] != null
                      ? <IOSNotificationAttachment>[
                          IOSNotificationAttachment(bigpicture),
                        ]
                      : <IOSNotificationAttachment>[],
                )
              : null,
        ),
        payload: json.encode(message.data));

使用的插件版本 #

• flutter_local_notifications: ^9.2.0
• firebase_messaging: ^11.2.5

推送Payload #

{
    "message": {
        "notification": {
            "title": "Welcome message",
            "body": "Firebase Nodification Success",
            "sound": "Default",
            "imageUrl": "https://cdn.pixabay.com/photo/2015/04/23/22/00/tree-736885__480.jpg"
        },
        "data": {
            "title": "Welcome message12",
            "body": "Firebase Nodification Success🙂",
            "click_action": "FLUTTER_NOTIFICATION_CLICK",
            "image": "https://cdn.pixabay.com/photo/2015/04/23/22/00/tree-736885__480.jpg",
            "status": "Received"
        }
    },
    "registrationToken": "**fcmtoken**"
}

Flutter环境信息 #

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.10.5, on macOS 12.5.1 21G83 darwin-arm, locale en-IN)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
[✓] Xcode - develop for iOS and macOS (Xcode 13.4)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2021.2)
[✓] VS Code (version 1.69.2)
[✓] Connected device (2 available)
[✓] HTTP Host Availability
• No issues found!

问题原因及解决方案 #

核心原因 #

iOS在后台/终止状态下，FCM推送的notification类型消息会由系统直接处理，不会触发Flutter端的消息回调，导致图片下载并添加附件的逻辑无法执行。同时Directory.systemTemp目录的文件在后台可能被系统清理，或系统无权限访问该目录文件用于通知附件。

解决步骤 #

1. 改用纯Data消息推送
   移除Payload中的notification字段，仅保留data字段。这样无论应用处于前台、后台还是终止状态，FCM都会将消息传递到Flutter的消息处理回调，确保图片下载逻辑正常执行。修改后的Payload示例：

   {
       "message": {
           "data": {
               "title": "Welcome message12",
               "body": "Firebase Nodification Success🙂",
               "click_action": "FLUTTER_NOTIFICATION_CLICK",
               "image": "https://cdn.pixabay.com/photo/2015/04/23/22/00/tree-736885__480.jpg",
               "status": "Received"
           }
       },
       "registrationToken": "**fcmtoken**"
   }
   

2. 更换图片存储目录
   替换Directory.systemTemp为应用文档目录（需依赖path_provider插件），系统对该目录文件的访问权限更稳定，不会轻易清理。修改下载路径示例：

   import 'package:path_provider/path_provider.dart';
   
   // 获取应用文档目录
   final dir = await getApplicationDocumentsDirectory();
   bigpicture = await DownloadUtil.downloadfiles(url,
       "${dir.path}/bigpicture.${(format.isEmpty || formatlist.contains(format)) ? format : "jpg"}");
   

3. 配置后台权限

   • 在Xcode中开启应用的后台模式，勾选“Remote notifications”；
   • 确保Info.plist中UIBackgroundModes包含remote-notification。

4. 验证附件合规性
   确保下载的图片文件大小不超过iOS通知附件限制（通常≤10MB），且文件路径为应用有权访问的目录。

内容的提问来源于stack exchange，提问作者VIGNESH B