从 Swift 函数中的异步调用返回数据 [英] Returning data from async call in Swift function

问题描述

我在我的 Swift 项目中创建了一个实用程序类，用于处理所有 REST 请求和响应.我已经构建了一个简单的 REST API，所以我可以测试我的代码.我创建了一个需要返回 NSArray 的类方法，但是因为 API 调用是异步的，所以我需要从异步调用中的方法返回.问题是异步返回无效.如果我在 Node 中执行此操作，我会使用 JS 承诺，但我无法找出适用于 Swift 的解决方案.

I have created a utility class in my Swift project that handles all the REST requests and responses. I have built a simple REST API so I can test my code. I have created a class method that needs to return an NSArray but because the API call is async I need to return from the method inside the async call. The problem is the async returns void. If I were doing this in Node I would use JS promises but I can't figure out a solution that works in Swift.

import Foundation

class Bookshop {
    class func getGenres() -> NSArray {
        println("Hello inside getGenres")
        let urlPath = "http://creative.coventry.ac.uk/~bookshop/v1.1/index.php/genre/list"
        println(urlPath)
        let url: NSURL = NSURL(string: urlPath)
        let session = NSURLSession.sharedSession()
        var resultsArray:NSArray!
        let task = session.dataTaskWithURL(url, completionHandler: {data, response, error -> Void in
            println("Task completed")
            if(error) {
                println(error.localizedDescription)
            }
            var err: NSError?
            var options:NSJSONReadingOptions = NSJSONReadingOptions.MutableContainers
            var jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: options, error: &err) as NSDictionary
            if(err != nil) {
                println("JSON Error (err!.localizedDescription)")
            }
            //NSLog("jsonResults %@", jsonResult)
            let results: NSArray = jsonResult["genres"] as NSArray
            NSLog("jsonResults %@", results)
            resultsArray = results
            return resultsArray // error [anyObject] is not a subType of 'Void'
        })
        task.resume()
        //return "Hello World!"
        // I want to return the NSArray...
    }
}

推荐答案

可以通过callback，在async call里面调用callback

You can pass callback, and call callback inside async call

类似:

class func getGenres(completionHandler: (genres: NSArray) -> ()) {
    ...
    let task = session.dataTaskWithURL(url) {
        data, response, error in
        ...
        resultsArray = results
        completionHandler(genres: resultsArray)
    }
    ...
    task.resume()
}

然后调用这个方法:

override func viewDidLoad() {
    Bookshop.getGenres {
        genres in
        println("View Controller: (genres)")     
    }
}

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