条件绑定的初始化程序必须具有可选类型,而不是'AnyObject - Approach

Question

以下代码抛出一条消息,指出"条件绑定的初始化程序必须具有可选类型,而不是'AnyObject'"

    func parseData2(){
        var data:NSData?


        if let data2 = data  {
            do {
                let details = try NSJSONSerialization.JSONObjectWithData(data2, options: .AllowFragments)

                if let actualDetails = details where actualDetails.isKindOfClass(NSDictionary) {
                    print("Parse Data")
                }

            }catch {
                print("Error \(error)")
            }
        }

    }

为解决上述错误,我使用了以下代码.

    func parseData2(){
        var data:NSData?


        if let data2 = data  {
            do {
                let details:AnyObject = try NSJSONSerialization.JSONObjectWithData(data2, options: .AllowFragments)

                if let actualDetails:AnyObject = details where actualDetails.isKindOfClass(NSDictionary) {
                    print("Parse Data")
                }

            }catch {
                print("Error \(error)")
            }
        }

    }

有没有比上面更好的方法或我的代码可能会崩溃？

考虑到nil check,键入check然后键入cast check,还有一个我想要添加的代码.Swift背后的原因提供了很大的灵活性,但很难解决问题.假设我有一个字典,cityDetails,我正在尝试获取self.cityZipCode和self.cityIdentifier的数据,这些数据是可选的,定义为var cityZipCode:Int？和var cityIdentifier:Int？

if let cityBasic = cityDetails["basicDetails"] where 
cityBasic!.isKindOfClass(NSDictionary) {

self.cityZipCode = (cityBasic as! NSDictionary)["zip"].integerValue ?? 0

self.cityIdentifier =  (cityBasic as! NSDictionary)["cityId"].integerValue ?? 0

}

Answer 1

无需打开结果try.它不是可选的.你需要将结果try转换为NSDictionary.使用as?向下转型了.

最佳实践:完全访问返回的错误以获得良好的错误处理

func parseData2(){
    var data:NSData?

    if let data2 = data  {
        do {
            let details = try NSJSONSerialization.JSONObjectWithData(data2, options: .AllowFragments)

            if let detailsDict = details as? NSDictionary {
                print("Parse Data")
            } else if let detailsArray = details as? NSArray {
                print("array")
            }

        } catch {
            print("Error \(error)")
        }
    }
}

快速而肮脏:错误处理不适合我!

func parseData2(){
    var data:NSData?

    if let data2 = data  {

        let details = try? NSJSONSerialization.JSONObjectWithData(data2, options: .AllowFragments)

        if let detailsDict = details as? NSDictionary {
            print("Parse Data")
        } else {
            print("details might be nil, or not an NSDictionary")
        }
    }
}

坏屁股模式:崩溃是功能

func parseData2(){
    var data:NSData?

    if let data2 = data  {

        let details = try! NSJSONSerialization.JSONObjectWithData(data2, options: .AllowFragments) as! NSDictionary

    }
}

多个unwraps的一些额外信息:将以下代码放在操场上.

struct SomeStruct {
    var anOptional : Int?
    init() {
    }
}

func unwrapWithIfLet() {

    if let unWrappedStruct = myStruct, let unWrappedSomething = unWrappedStruct.anOptional {
        print("multiple optional bindings succeeded")
        // both unWrappedStruct and unWrappedSomething are available here
    } else {
        print("something is nil")
    }
}

func unwrapWithGuard() {

    guard let unWrappedStruct = myStruct, let unWrappedSomething = unWrappedStruct.anOptional else {
        print("something is nil")
        return
    }
    print("multiple optional bindings succeeded")
    // both unWrappedStruct and unWrappedSomething are available here
}


var myStruct : SomeStruct?

//unwrapWithGuard()
//unwrapWithIfLet()

myStruct = SomeStruct()
myStruct!.anOptional = 1

unwrapWithGuard()
unwrapWithIfLet()