swift - 在类 init() 中使用 CLGeocoder

Question

我想要一个能够使用CLGeocoder 获取国家/地区名称的类。下面的代码不起作用可能是因为在 CLGeocoder 完成运行之前将变量 country 分配给了 self.country。我该怎么做才能让 self.country 实际上从 CLGeocoder 获取国家/地区名称？

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，您可以很好地看到这一点

您需要记住，当您在主视图 Controller 中定义 Place 的实例时，最初不会定义 place.country 的值。您可以在延迟后再次检查它以获取更新版本，或者您可以添加一个委托(delegate)，以便它在值准备就绪时更新父 Controller

这是简单的版本

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       
        })
    }
}

这是带有委托(delegate)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)")
}