Question

我试图同时为多个地点进行反向地理编码。所以我创建了一个函数a = [[1234,'1/8/2014'],[4123,'1/3/2014'],[5754,'1/12/2014'],[8548,'11/8/2014'],[9469,'11/9/2013'],[3564,'1/8/2013']] data = {} result = [] for item in a: year = item[1].split('/')[-1] data[year] = data.get(year, []) + [item[0]] for key in data.keys(): items = data.get(key) avg = sum(items)/len(items) result.extend([key, avg]) print(result)。问题是，自performReverseGeoLocation封闭后，CLGeocoder().reverseGeocodeLocation将首先执行。如何更改这些函数，以便在for循环中的所有completionHandlerLocations完成后调用者将获得完成处理程序？

我尝试过的代码：

CLGeocoder().reverseGeocodeLocation

Answer 1

您可以这样做：

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。

Answer 2

如上所述 i-am-jorf ，您可以创建DispatchGroup并在所有反向地理编码任务完成后等待通知：

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

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

    self.images.forEach { (location) in
        group.enter()

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

        CLGeocoder().reverseGeocodeLocation(location, completionHandler: { (placemark, error) in
            // do all your checks...
            if placemark != nil && placemark!.count > 0 {
                cities.append(placemark!.first!.locality!)
                countries.append(placemark!.first!.country!)
            }

            group.leave()
        })
    }

    group.notify(queue: DispatchQueue.main) {
        completionHandlerLocations(cities, countries)
    }
}

swift - 如何执行任务完成

2 个答案: