Question

class OAuthToken: NSObject, NSCoding {

var refreshToken: String?
var accessToken: String?
var scope: String?

convenience init?(refreshToken: String?, accessToken: String?, scope:String) {
    self.init()

    if let acutalRefreshToken = refreshToken as String? {
        self.refreshToken = acutalRefreshToken
    } else {
        return nil
    }
    if let actualAccessToken = accessToken as String? {
        self.accessToken = actualAccessToken
    }else {
        return nil
    }
    self.scope = scope
}

convenience init?(attributes: Dictionary<String,AnyObject>, scope: String) {
    var aRefreshToken: String!
    var anAccessToken: String?
    aRefreshToken = attributes["refresh_token"] as String?
    anAccessToken = attributes["access_token"] as String?
    let token = self.init(refreshToken: aRefreshToken, accessToken: anAccessToken, scope: scope) as OAuthToken // () is not convertible to OAuthToken
    if token != nil {
        storeInKeyChain()
    } else {
        return nil
    }
}
}

当你在另一个内部调用嵌套的可用初始值设定项时，如何检查nil的可用初始值设定项？

let token = self.init(refreshToken: aRefreshToken, accessToken: anAccessToken, scope: scope)想要返回()类型的对象，而不是可转换为我的类。我如何使用此模式并仅将对象存储到钥匙串（如果它实际上已成功创建？）

Answer 1

我认为当你调用超类的可用初始值设定项时，如果它失败则会有隐式返回。

事实上，关于Failable Initializers的文档指出：

如果由于名称空值而导致超类初始化失败，则整个初始化过程立即失败，并且不再执行初始化代码

Answer 2

正如Antonio所说（+1），您不必测试其他初始化程序是否成功。如果失败，则当前初始化会立即失败。例如，考虑：

convenience init?(attributes: Dictionary<String,AnyObject>, scope: String) {
    let aRefreshToken = attributes["refresh_token"] as String?
    let anAccessToken = attributes["access_token"] as String?
    self.init(refreshToken: aRefreshToken, accessToken: anAccessToken, scope: scope)
    storeInKeyChain()
}

如果storeInKeyChain()失败，则不会调用init(refreshToken:, accessToken:, scope:)函数。请参阅The Swift Programming Language: Initialization的初始化失败的传播部分。

如何在Swift中使用嵌套方便的可用初始值设定项检查nil？

2 个答案: