Swift：调用中的额外参数 'error'

Question

我目前正在使用 Swift 2.0 和 Xcode Beta 2 开发我的第一个 iOS 应用程序。它读取外部 JSON 并在 table 用数据查看。但是，我遇到了一个似乎无法修复的奇怪小错误：

Extra argument 'error' in call

这是我的代码片段：

let task = session.dataTaskWithURL(url!, completionHandler: {data, response, error -> Void in
            print("Task completed")

            if(error != nil){
                print(error!.localizedDescription)
            }

            var err: NSError?

            if let jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as? NSDictionary{

                if(err != nil){
                    print("JSON Error \(err!.localizedDescription)")
                }

                if let results: NSArray = jsonResult["results"] as? NSArray{
                    dispatch_async(dispatch_get_main_queue(), {
                        self.tableData = results
                        self.appsTableView!.reloadData()
                    })
                }
            }
        })

在这一行抛出错误：

if let jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as? NSDictionary{

有人可以告诉我我做错了什么吗？

Answer 1

随着 Swift 2，NSJSONSerialization 的 signature 已更改，以符合新错误处理系统。

这是一个如何使用它的例子：

do {
    if let jsonResult = try NSJSONSerialization.JSONObjectWithData(data, options: []) as? NSDictionary {
        print(jsonResult)
    }
} catch let error as NSError {
    print(error.localizedDescription)
}

随着 Swift 3，NSJSONSerialization 的 name 及其方法发生了变化，根据 the Swift API Design Guidelines.

这是同一个例子：

do {
    if let jsonResult = try JSONSerialization.jsonObject(with: data, options: []) as? [String:AnyObject] {
        print(jsonResult)
    }
} catch let error as NSError {
    print(error.localizedDescription)
}

Answer 2

在 Swift 2 中发生了变化，接受 error 参数的方法被转换为抛出该错误的方法，而不是通过 inout 参数返回错误。通过查看 Apple documentation:

HANDLING ERRORS IN SWIFT: In Swift, this method returns a nonoptional result and is marked with the throws keyword to indicate that it throws an error in cases of failure.

You call this method in a try expression and handle any errors in the catch clauses of a do statement, as described in Error Handling in The Swift Programming Language (Swift 2.1) and Error Handling in Using Swift with Cocoa and Objective-C (Swift 2.1).

最短的解决方案是使用 try? 其中 returns nil 如果发生错误：

let message = try? NSJSONSerialization.JSONObjectWithData(receivedData, options:.AllowFragments)
if let dict = message as? NSDictionary {
    // ... process the data
}

如果您也对该错误感兴趣，可以使用 do/catch:

do {
    let message = try NSJSONSerialization.JSONObjectWithData(receivedData, options:.AllowFragments)
    if let dict = message as? NSDictionary {
        // ... process the data
    }
} catch let error as NSError {
    print("An error occurred: \(error)")
}

Answer 3

这已在 Swift 3.0 中更改。

 do{
            if let responseObj = try JSONSerialization.jsonObject(with: results, options: .allowFragments) as? NSDictionary{

                if JSONSerialization.isValidJSONObject(responseObj){
                    //Do your stuff here
                }
                else{
                    //Handle error
                }
            }
            else{
                //Do your stuff here
            }
        }
        catch let error as NSError {
                print("An error occurred: \(error)") }

Swift：调用中的额外参数 'error'

Swift: Extra argument 'error' in call

ios

swift2

xcode7-beta2