从函数返回多个值时出现 Swift 错误

Question

我不明白我做错了什么

---

我有一个加载帖子及其评论的应用程序。 View Controller 从另一个文件请求一个函数，该函数返回(响应？评论？)

我得到一个错误:

Initializer for conditional binding must have Optional type, not '(ActionResult?, [PostComment]?)'

对于行

if let (response, comments) = (response, comments )

我做错了什么？

评论 View Controller

postComments.loadCommentForPost(id: postId) { (response, comments) in
            // ERROR here: Initializer for conditional binding must have Optional type, not '(ActionResult?, [WorldMessageComment]?)'
            if let (response, comments) = (response, comments ) {
                if response!.success == 1 {
                    DispatchQueue.main.async(execute: {() -> Void in
                            self.comments = comments!
                            self.tableView.reloadData()
                        })
                } else {
                    DispatchQueue.main.async(execute: {() -> Void in
                        self.handleResponses.displayError(title: response!.title, message: response!.message)
                    })
                }
            }
        }

评论函数

func loadCommentsForPost(id: Int, completion: @escaping ((ActionResult?), [PostComment]?)->()){

        // downloading the data and then

        let comments : [PostComment] = ...

        // Succesful
        return completion((ActionResult(success: 1, title: responseTitle, message: responseMessage)), comments)

    }

Answer 1

问题在行中:

if let (response, comments) = (response, comments ) {

你基本上做的是在赋值的右侧创建一个新的非可选元组(有两个可选组件)，所以编译器提示你不能使用 if let with非可选类型。

您实际上可以认为 loadCommentsForPost 返回的元组已经在回调的参数中“拆分”，因此您可以分别处理 response 和 comments。

postComments.loadCommentForPost(id: postId) { response, comments in
    if let response = response, let comments = comments {
       if response.success == 1 {
       ...