attachment property Null safety
@JsonKey(fromJson: NIMMessageAttachment.fromJson, toJson: NIMMessageAttachment.toJson), read / write
消息附件对象。仅当MsgType为非text时有效
Implementation
@JsonKey(
fromJson: NIMMessageAttachment.fromJson,
toJson: NIMMessageAttachment.toJson)
NIMMessageAttachment? attachment;