无法将类型“()”的值转换为预期的参数类型“(() -> Void)？”

Question

我遇到了这样的问题，请问大家有什么办法解决吗？ Xcode 11.2，SwiftUI

.onAppear(perform: self.sessionChat.loadMsgInChatRoom(chatRoom: chatRoom)) //then an error

func loadMsgInChatRoom(chatRoom: String) {
        let db = Firestore.firestore()
        db.collection("chatRoom").document(chatRoom).collection("msg")
            .addSnapshotListener { (querySnapshot, err) in
            if err != nil {
                print((err?.localizedDescription)!)
                return
            }
            for i in querySnapshot!.documentChanges {
                if i.type == .added {
                    let user = i.document.get("user") as! String
                    let msg = i.document.get("msg") as! String
                    let idUser = i.document.get("idUser") as! String
                    let dateMsg = i.document.get("dateMsg") as! String
                    let id = i.document.documentID

                    self.msgs.append(dataMessges(id: id, user: user, msg: msg, idUser: idUser, dateMsg: dateMsg))
                }
            }
        }
    }

Answer 1

.onAppear 需要一个闭包，所以我认为需要大括号

.onAppear(perform: { self.sessionChat.loadMsgInChatRoom(chatRoom: chatRoom) } )

或更简单的方法：

.onAppear { 
     self.sessionChat.loadMsgInChatRoom(chatRoom: chatRoom)
}