如何等到 CLGeocoder 完成工作答案

【问题标题】：How to wait until CLGeocoder finish its work如何等到 CLGeocoder 完成工作
【发布时间】：2021-08-30 19:51:01
【问题描述】：

我有以下来自 GPS 坐标的功能地理编码地址

private func getAddressFromLocation(forLocation: CLLocationCoordinate2D) {
    let geoCoder = CLGeocoder()
    geoCoder.reverseGeocodeLocation(CLLocation(latitude: forLocation.latitude, longitude: forLocation.longitude), completionHandler: {(places, error) in
        guard error == nil else {
            return
        }
        let place: CLPlacemark = places!.first!
        var address: [String] = []
        if place.country != nil { address.append(place.country!) }
        if place.postalCode != nil { address.append(place.postalCode!) }
        if place.locality != nil { address.append(place.locality!) }
        if place.thoroughfare != nil { address.append(place.thoroughfare!) }
        self.fullAddress = address.joined(separator: ",")
    })
}

从我的应用程序的另一部分调用函数，我想知道如何确保程序将等到 fullAddress 变量获得值（函数完成）。我试图将函数调用放入同步调度队列，但没有帮助。感谢您的任何建议。

【问题讨论】：

不要问，要告诉。意思是：不要等待，通知。请搜索completion handler

标签： swift clgeocoder

【解决方案1】：

我愿意：

使用Result 类型的完成处理程序；
将 UI 更新与反向地理编码解耦；
使用Contacts框架中的CNPostalAddressFormatter来格式化地址；

例如


enum GeocodeError: Error {
    case notFound
}

let geocoder = CLGeocoder()

func getAddress(for coordinate: CLLocationCoordinate2D, completion: @escaping (Result<String, Error>) -> Void) {
    let location = CLLocation(latitude: coordinate.latitude, longitude: coordinate.longitude)
    geocoder.reverseGeocodeLocation(location) { places, error in
        guard error == nil, let address = places?.first?.postalAddress else {
            completion(.failure(error ?? GeocodeError.notFound))
            return
        }

        let formatter = CNPostalAddressFormatter()
        let string = formatter.string(from: address)
            .components(separatedBy: "\n")
            .joined(separator: ", ")
        completion(.success(string))
    }
}

然后这样称呼它：

getAddress(for: coordinate) { result in
    switch result {
    case .failure(let error):   // update UI to report error, if any
    case .success(let address): // update UI to show address
    }
}

【讨论】：

【解决方案2】：

是的，完成处理程序将成为您的朋友：

typealias CompletionHandler = (_ success:Bool) -> Void

private func getAddressFromLocation(forLocation: CLLocationCoordinate2D, completionHandler: @escaping CompletionHandler) {
    let geoCoder = CLGeocoder()
    geoCoder.reverseGeocodeLocation(CLLocation(latitude: forLocation.latitude, longitude: forLocation.longitude), completionHandler: {(places, error) in
        guard error == nil else {
            completionHandler(false)
            return
        }
        let place: CLPlacemark = places!.first!
        var address: [String] = []
        if place.country != nil { address.append(place.country!) }
        if place.postalCode != nil { address.append(place.postalCode!) }
        if place.locality != nil { address.append(place.locality!) }
        if place.thoroughfare != nil { address.append(place.thoroughfare!) }
        print("address: \(address.joined(separator: ","))")
        completionHandler(true)
    })
}

你可以这样称呼它：

getAddressFromLocation(forLocation: CLLocationCoordinate2D()) { success in
    if success {
        //once address is fetched, this will be triggered.
    }
}

【讨论】：

谢谢你，Brendan C。它现在可以完美运行了。