从 Swift 函数中的异步调用返回数据

本文介绍了从 Swift 函数中的异步调用返回数据的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 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 = "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)") } }