无法从 Google-Books JSON API 中获取值

Question

我正在使用条形码扫描仪获取使用 google 本书 api 扫描书籍的数据。我成功调用了 API 并得到了 JSON object 返回。

我正在尝试获取遵循路径 items.volumeInfo.title 的书名。

当我在 API 返回的 JSON object 上调用 valueForPath 并尝试打印它（标题）时，我最终打印：

Optional(( "A Dance with Dragons" ))

我似乎无法弄清楚如何从打印的可选字符串中实际获取字符串。我尝试了 as! String 和 jsonResult.valueForKeyPath("items.volumeInfo.title")!，但第一个只是向我抱怨，第二个只是删除了可选的和外部的括号集。

func getBookInfo(isbn: String) {
        var url: String = "https://www.googleapis.com/books/v1/volumes?q=isbn:" + isbn;
        var request: NSMutableURLRequest = NSMutableURLRequest()
        request.URL = NSURL(string: url)
        request.HTTPMethod = "GET"

        NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue(), completionHandler:{ (response:NSURLResponse!, data: NSData!, error: NSError!) -> Void in
            var error: AutoreleasingUnsafeMutablePointer<NSError?> = nil
            let jsonResult: NSDictionary! = NSJSONSerialization.JSONObjectWithData(data, options:NSJSONReadingOptions.MutableContainers, error: error) as? NSDictionary

            if (jsonResult != nil) {

                println(jsonResult.valueForKeyPath("items.volumeInfo.title"))
                //self.json.setValue(jsonResult.valueForKeyPath("items.volumeInfo.title")!, forKey: "title")

            } else {
                GlobalConstants.AlertMessage.displayAlertMessage("Error fetching data from barcode, please try again.", view: self)
            }


        })
    }

Answer 1

您从 API 获得的响应是一组标题。

我建议使用 if let 解包您从 KVC 获得的 Optional 值，并将结果类型转换为 Swift 字符串数组。

Swift 1

func getBookInfo(isbn: String) {
    var url: String = "https://www.googleapis.com/books/v1/volumes?q=isbn:" + isbn
    var request: NSMutableURLRequest = NSMutableURLRequest()
    request.URL = NSURL(string: url)
    request.HTTPMethod = "GET"

    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue(), completionHandler:{ (response:NSURLResponse!, data: NSData!, error: NSError!) -> Void in
        var error: AutoreleasingUnsafeMutablePointer<NSError?> = nil

        if let jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: nil, error: error) as? NSDictionary {

            if let arrayOfTitles = jsonResult.valueForKeyPath("items.volumeInfo.title") as? [String] {
                let titles = ", ".join(arrayOfTitles)
                println(titles)
            } else {
                // error: no title found
            }

        } else {

            GlobalConstants.AlertMessage.displayAlertMessage("Error fetching data from barcode, please try again.", view: self)

        }

    })
}

getBookInfo("0553283685")  // prints "Hyperion"

Swift 2

对于这个版本，我们使用 NSURLSession，因为 NSURLConnection 现已弃用。

func getBookInfo(isbn: String) {
    let urlString = "https://www.googleapis.com/books/v1/volumes?q=isbn:" + isbn
    if let url = NSURL(string: urlString) {
        NSURLSession.sharedSession().dataTaskWithURL(url, completionHandler: {data, _, error -> Void in
            if let error = error {
                print(error.localizedDescription)
            } else {
                if let data = data,
                    jsonResult = try? NSJSONSerialization.JSONObjectWithData(data, options: []),
                    arrayOfTitles = jsonResult.valueForKeyPath("items.volumeInfo.title") as? [String] {
                    let titles = arrayOfTitles.joinWithSeparator(", ")
                    print(titles)
                } else {
                    GlobalConstants.AlertMessage.displayAlertMessage("Error fetching data from barcode, please try again.", view: self)
                }
            }
        }).resume()
    }
}

getBookInfo("0553283685") // prints "Hyperion"

Swift 3

与 Swift 2 相同，但有一些语法更改。我还添加了 "authors" 示例，我现在使用 guard。只是为了展示与前面示例不同的东西。

func getBookInfo(isbn: String) {
    guard let url = URL(string: "https://www.googleapis.com/books/v1/volumes?q=isbn:\(isbn)") else {
        print("the url is not valid")
        return
    }
    URLSession.shared().dataTask(with: url, completionHandler: {data, response, error -> Void in
        guard error == nil else {
            print(response)
            print(error!.localizedDescription)
            return
        }
        guard let data = data else {
            print("no error but no data")
            print(response)
            return
        }
        guard let jsonResult = try? JSONSerialization.jsonObject(with: data, options: []) else {
            print("the JSON is not valid")
            return
        }
        if let arrayOfTitles = jsonResult.value(forKeyPath: "items.volumeInfo.title") as? [String] {
            print(arrayOfTitles)
        }
        if let arrayOfAuthors = jsonResult.value(forKeyPath: "items.volumeInfo.authors") as? [[String]] {
            print(arrayOfAuthors)
        }
    }).resume()
}

getBookInfo(isbn: "0553283685")

无法从 Google-Books JSON API 中获取值

Can't get value from Google-Books JSON API

json

google-books

ios

kvc

swift