ios - swift - 如何完成任务

Question

我正在尝试同时对多个位置进行反向地理编码。所以我创建了一个函数 performReverseGeoLocation。问题是，由于 CLGeocoder().reverseGeocodeLocation 是一个闭包，因此 completionHandlerLocations 将首先执行。我如何更改这些函数，以便调用者在 for 循环内的所有 CLGeocoder().reverseGeocodeLocation 完成后获得完成处理程序？

我试过的代码:

private func getImageLocation() {
    performReverseGeoLocation(completionHandlerLocations: { (cities, countries) in
        print("***** This is executed before the reverse geo code location is done")
    })
}

private func performReverseGeoLocation(completionHandlerLocations: @escaping (_ cities: [String], _ countries: [String]) -> Void) {

    var cities = [String]()
    var countries = [String]()

    for image in self.images {
        let longitude = image.longitude
        let latitude = image.latitude

        let location = CLLocation(latitude: latitude, longitude: longitude)

        CLGeocoder().reverseGeocodeLocation(location, completionHandler: {(placemarks, error) -> Void in
            print("***** This is executed after completionHandlerLocations is done")
            if error != nil {
                self.alertError("Reverse geocoder failed with error" + (error?.localizedDescription)!)
                return
            }

            if placemarks!.count > 0 {
                let pm = placemarks![0]

                let country = pm.country
                let city = pm.locality


                if (!cities.contains(city!)) {
                    cities.append(city!)
                }

                if (!countries.contains(country!)) {
                    countries.append(country!)
                }
            }
            else {
                self.alertError("Fail to perform reverse geo location")
            }
        })
    }
    // THIS IS WILL EXECUTED FIRST
    completionHandlerLocations(cities, countries)
}

Answer 1

你可以这样做:

var count = 0

for image in self.images {
     ...
     CLGeocoder().reverseGeocodeLocation(location) {
          // get result 

          counter ++

          if count == self.images.count { // finish all requests
               completionHandlerLocations(cities, countries)
          }

     }
}

这是最简单的方法。