ios - 将字符串附加到字典时出错

Question

我有这个结构:

public struct GIReservation{
    var name: String!
    var mobile: String! 
    var datetime: String!
    var people: Int!
    var info: String?
    var id: String?
}

另一个类实现了:

public class GIReservationCalendarViewModel {

    public func newReservation(reservation: GIReservation) {
        let manager = AFHTTPRequestOperationManager()
        manager.requestSerializer.setValue(Authenticator.getAccessToken(), forHTTPHeaderField: API_HEADER_ACCESSTOKEN)
        var parameters = ["name": reservation.name, "mobile": reservation.mobile, "datetime" : reservation.datetime, "people" : reservation.people]

        if let safeInfo = reservation.info {
            parameters["info"] = safeInfo
        }
        manager.POST(self.reservationsURL, parameters: parameters, success: { (operation: AFHTTPRequestOperation!, responseObject: AnyObject!) -> Void in
            println("saved!")
        }) { (operation: AFHTTPRequestOperation!, error: NSError!) -> Void in
            println("OPS!")
        }

    }
}

但是在这条线上:

parameters["info"] = safeInfo

然后我得到了这个错误

cannot assign to the result of this expression

但是……为什么!？

Answer 1

parameters 被推断为 NSDictionary，因为您使用的是 String! 和 Int! 等混合类型。

public struct GIReservation{
    var name: String!
    var mobile: String! 
    var datetime: String!
    var people: Int!
    var info: String?
    var id: String?
}

// Here an immutable NSDictionary is inferred as type by the compiler
// because you are mixing reservation.people witch is an Int! with
// other String! types
var parameters = ["name": reservation.name, "mobile": reservation.mobile, "datetime" : reservation.datetime, "people" : reservation.people]

if let safeInfo = reservation.info {
    parameters["info"] = safeInfo
}

但是您不能向 NSDictionary 添加任何内容，它是不可变的。因此错误“无法分配给该表达式的结果”。您将需要 NSMutableDictionary:

var parameters: NSMutableDictionary = ["name": reservation.name, "mobile": reservation.mobile, "datetime" : reservation.datetime, "people" : reservation.people]

if let safeInfo = reservation.info {
    parameters["info"] = safeInfo
}

或者 Swift:[String:AnyObject]

var parameters: [String:AnyObject] = ["name": reservation.name, "mobile": reservation.mobile, "datetime" : reservation.datetime, "people" : reservation.people]

if let safeInfo = reservation.info {
    parameters["info"] = safeInfo
}