Question

我的具体任务是创建一个可用的初始化程序，它接受字典作为参数并初始化结构的所有存储属性。键应该是＆＃34;标题＆＃34;，＆＃34;作者＆＃34;，＆＃34;价格＆＃34;和＆＃34; pubDate＆＃34;。

struct Book {
    let title: String
    let author: String
    let price: String?
    let pubDate: String?

我不知道该怎么做。我已经走了几条不同的路线，阅读了关于字典和初始化器的文档而没有任何运气。我大多不确定如何为init方法设置参数。这是（抽象）我的想法

init?([dict: ["title": String], ["author": String], ["price": String], ["pubDate": String]]) {
        self.title = dict["title"]
        self.author = dict["author"]
        self.price = dict["price"]
        self.pubDate = dict["pubDate"]
    }

我错过了什么？

Answer 1

试试这个：

struct Book {
    let title: String
    let author: String
    let price: String?
    let pubDate: String?

    init?(dict: [String: String]) {
        guard dict["title"] != nil && dict["author"] != nil else {
            // A book must have title and author. If not, fail by returning nil
            return nil
        }

        self.title = dict["title"]!
        self.author = dict["author"]!
        self.price = dict["price"]
        self.pubDate = dict["pubDate"]
    }
}

// Usage:
let book1 = Book(dict: ["title": "Harry Potter", "author": "JK Rowling"])
let book2 = Book(dict: ["title": "Harry Potter", "author": "JK Rowling", "price": "$25"])
let book3 = Book(dict: ["title": "A book with no author"]) // nil

这说明一本书必须有author和title。如果它没有任何一个，它将失败。 price和pubDate是可选的。

如何从String和String初始化字典？

1 个答案: