swift - 进行可选链接的好方法

Question

我目前在我的代码中这样做是为了处理可选项...

我做一个

fetchedResultController.performFetch(nil)

let results = fetchedResultController.fetchedObjects as [doesnotmatter]

// add all items to server that have no uid
for result in results {

    let uid = result.valueForKey("uid") as String?
    if uid == nil
    {
        let name = result.valueForKey("name") as String?

        let trainingday = result.valueForKey("trainingdayRel") as Trainingdays?
        if let trainingday = trainingday
        {
            let trainingUID  = trainingday.valueForKey("uid") as String?
            if let trainingUID = trainingUID
            {

                let urlstring = "http://XXXX/myGym/addTrainingday.php?apikey=XXXXXX&date=\(date)&appid=47334&exerciseUID=\(exerciseUID)"
                let sUrl = urlstring.stringByAddingPercentEscapesUsingEncoding(NSASCIIStringEncoding)
                let url = NSURL(string: sUrl!)

                // save the received uid in our database
                if let dictionary = Dictionary<String, AnyObject>.loadJSONFromWeb(url!)
                {
                    trainingday.setValue(uid, forKey: "uid")
                }
                self.managedObjectContext!.save(nil)
            }

        }

    }

}

实际上我还需要为每个“if let”语句添加一个“else”子句。这对我来说似乎是非常糟糕的代码!有没有更好的方法来做到这一点？

Answer 1

是的，使用 switch-case 和模式匹配你可以实现这个:

var x : SomeOptional?
var y : SomeOptional?

switch (x, y)
{
    case (.Some(let x), .Some(let y)): doSomething() // x and y present
    case (.None(let x), .Some(let y)): doSomethingElse() // x not present, but y
    // And so on for the other combinations
    default: break
}

看看这篇博文:Swift: Unwrapping Multiple Optionals

编辑(略微偏离主题且基于观点):这是我最喜欢的 Swift 功能之一。它还让您只需很少的代码即可实现 FSM，这非常棒。