小编Jos*_*nor的帖子

我试图调用根控制器,我不知道调用它的代码.我正在使用条件,它将检查以前的视图控制器是什么,并且将根据它是什么来运行代码块.这是我的代码:

SecondViewController

override func viewDidLoad ( ) {
     super.viewDidLoad ( )

     let previousController = storyboard!.instantiateViewControllerWithIdentifier ("firstViewController") as? FirstViewController

     //HELP IN LINE BELOW
     //if root view controller == previousController {
              //run some code
     //}
}

我试图将我的代码转换为Swift 3.0,并且在使用迁移工具后我无法转换某个代码块.

以前的SWIFT 3.0迁移:

import Foundation

extension NSDate {
    convenience init(posixTime: Double) {
        self.init(timeIntervalSince1970: Double(posixTime) / 1000.0)
    }
}

迁移工具之后:

extension Date {
    init(posixTime: Double) {
        //ERROR IN THE LINE BELOW: "'init' is a member of the type; use 'type(of: ...)' to initialize a new object of the same dynamic type"
        (self as NSDate).init(timeIntervalSince1970: Double(posixTime) / 1000.0)
    }
}

我按照Xcodes的建议将"init"替换为"type(of:init)":

extension Date {
    init(posixTime: Double) {
        //ERROR IN THE LINE BELOW: "Expected expression in list of expressions"
        (self as NSDate).type(of: …

我正在为我的应用程序添加一个 mapKit，并将地图的中间设置为人员当前位置（以纬度和经度为单位）。我能够让它工作，但是，它经常更新。我只希望它在加载应用程序时更新一次，然后不再更新。可能每2分钟更新一次。这是我的代码：

func locationManager(manager: CLLocationManager!,
    didUpdateLocations locations: [AnyObject]!)
{
    var latestLocation = locations.last as! CLLocation


    let location = CLLocationCoordinate2D(latitude: latestLocation.coordinate.latitude, longitude: latestLocation.coordinate.longitude)
    let span = MKCoordinateSpanMake(0.015, 0.015)

    //Let our point be the center of our span
    //region holds value of span and location
    let region = MKCoordinateRegion(center: location, span: span)

    //set up region on mapView
    mapView.setRegion(region, animated: true)

    //MKPointAnnotation defines a concrete annotation
    let annotation = MKPointAnnotation()
}

我在return语句中无法理解这种语法.我不确定它是否是Swift 2.0中的新功能,但它是什么？和:意思是？这个问号是否可选,即使间隔？我很困惑,来自Objective-C背景.

private func doContainsUser(user: User) -> Bool {
    let isInverted = setOfDiff.contains(user)
    let wasInitiallyAdded = setOfCircleUsers.contains(user)

    //What does the ? and the : mean?
    return isInverted ? !wasInitiallyAdded : wasInitiallyAdded
}