在init()类中使用CLGeocoder

Question

我想有一个能够使用CLGeocoder获得国家名称的class。下面的代码不能工作，可能是因为变量country在CLGeocoder结束运行之前被赋值给了self.country。我该怎么做才能让self.country真正从CLGeocoder获取国家名称

class Place {

    let location: CLLocation
    let country: String

    init(location: CLLocation) {

        self.location = location

        var country = ""

        CLGeocoder().reverseGeocodeLocation(location, completionHandler: { (placemarks, _) in

            country = placemarks![0].country // I removed error and type checks for clarity       

        })

        self.country = country // self.country = "", but should be for example "Canada"

    }
}

Answer 1

您所要做的就是将self.country = country移到完成处理程序中。数据是异步返回的，如果您在country = placeholder和self.country行上设置断点，就可以很好地看到这一点

您需要记住，当您在主视图控制器中定义Place的实例时，place.country的值最初不会被定义。您可以在延迟一段时间后再次检查它以获取更新的版本，也可以添加一个委托，以便它在值就绪时更新父控制器

下面是简单的版本

class Place {

    let location: CLLocation
    var country: String = "Undefined"

    init(location: CLLocation) {

        self.location = location
        CLGeocoder().reverseGeocodeLocation(location, completionHandler: { (placemarks, _) in
            self.country = placemarks![0].country! // I removed error and type checks for clarity       
        })
    }
}

下面是带有委托的更优雅的版本

protocol CountryUpdatedDelegate
{
    func countryUpdated(_ country : String)
}

class Place {

    let location: CLLocation
    var country: String = "Undefined"

    var delegate : CountryUpdatedDelegate!

    init(location: CLLocation) {

        self.location = location

        CLGeocoder().reverseGeocodeLocation(location, completionHandler: { (placemarks, _) in
            guard let placeMarks = placemarks as [CLPlacemark]! else {
                return
            }
            self.country = placemarks![0].country! // I removed error and type checks for clarity
            self.delegate.countryUpdated(self.country)
        })
    }
}

然后在你的ViewController中

class ViewController: UIViewController, CountryUpdatedDelegate {

    let place = Place(location: location!)
    place.delegate = self





func countryUpdated(_ country : String)
{
    print("Country has now been updated \(country)")
}