iOS Swift - CLGeocoder completionHandler块

Question

我正在尝试将一个位置(CLLocation)解析为一个字符串。

    func locationToString (currentLocation: CLLocation) -> String? {
    var whatToReturn: String?
    CLGeocoder().reverseGeocodeLocation(currentLocation, completionHandler: { (placemarks: [AnyObject]!, error: NSError!) in
        if error == nil && placemarks.count > 0 {
            let location = placemarks[0] as CLPlacemark
            whatToReturn = "\(location.locality) \(location.thoroughfare) \(location.subThoroughfare)"

        }
    })
    return whatToReturn
}

显然，whatToReturn总是返回null，因为completionHandler在后台运行。当completionHandler完成时，我很难理解如何更新字符串？

谢谢。

Answer 1

如果要在textField中使用字符串(如注释中所示)，请执行以下操作：

func getAndDisplayLocationStringForLocation(currentLocation: CLLocation) {
    CLGeocoder().reverseGeocodeLocation(currentLocation, completionHandler: { (placemarks: [AnyObject]!, error: NSError!) in
        if error == nil && placemarks.count > 0 {
            let location = placemarks[0] as CLPlacemark
            self.textField.text = "\(location.locality) \(location.thoroughfare) \(location.subThoroughfare)"

        }
    })
}

但是，如果您需要访问其他地方，则可能以arg的形式传递一个闭包：

func getAndDisplayLocationStringForLocation(currentLocation: CLLocation, withCompletion completion: (string: String?, error?, error: NSError?) -> ()) {
    CLGeocoder().reverseGeocodeLocation(currentLocation, completionHandler: { (placemarks: [AnyObject]!, error: NSError!) in
        if error == nil && placemarks.count > 0 {
            let location = placemarks[0] as CLPlacemark
            completion(string: "\(location.locality) \(location.thoroughfare) \(location.subThoroughfare)", error: nil)

        } else {
            completion(nil, error)
        }
    })
}

然后像这样打电话：

yourModel.getAndDisplayLocationStringForLocation(someLocation) { (string: String?, error: NSError?) -> () in
    if (error == nil) {
        self.textField.text = string
    }
}

您可能希望以不同的方式处理错误等。这应该足够让你开始工作了。