这导致巨大的内存占用.您没有提到有关如何渲染线条的任何要求.因此,如果我们重新构建drawPolyline()方法以使用CLLocationCoordinate2D数组的实例变量,那么我们只使用一个,然后在更新UI之前处理所有json文件.内存使用量下降到更可管理的664.6 MB.

当然,渲染可能并不完全符合您的要求,如果是这种情况,您可能希望将CLLocationCoordinate2D数组重组为更合适的数据结构.

下面是您的ViewController类,其中重写的drawPolyline()为drawPolyline2()

import UIKit
import MapBox

class ViewController: UIViewController,MGLMapViewDelegate {

@IBOutlet var mapBoxView: MGLMapView!


fileprivate var coordinates = [[CLLocationCoordinate2D]]()
fileprivate var jsonData: NSData?

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view,typically from a nib.
    mapBoxView = MGLMapView(frame: view.bounds)
    mapBoxView.autoresizingMask = [.flexibleWidth,.flexibleHeight]

    // mapBoxView.setCenter(CLLocationCoordinate2D(latitude: 45.5076,longitude: -122.6736),//                             zoomLevel: 11,animated: false)

    mapBoxView.setCenter(CLLocationCoordinate2D(latitude: 1.290270,longitude: 103.851959),zoomLevel: 11,animated: false)


    view.addSubview(self.mapBoxView)


    mapBoxView.delegate = self
    mapBoxView.allowsZooming = true

    drawPolyline2()
    //newWay()
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}



func drawPolyline2() {

    DispatchQueue.global(qos: .background).async {

        if let path = Bundle.main.path(forResource: "KMLMAPNew",ofType: "json") {
            let fileURL = URL(fileURLWithPath: path)
            if let data = try? Data(contentsOf: fileURL) {

                do {

                    let dictionary = try JSONSerialization.jsonObject(with: data as Data,AnyObject>

                    if let features = dictionary?["features"] as? Array<AnyObject> {

                        print("** START **")

                        for feature in features {
                            guard let feature = feature as? Dictionary<String,AnyObject> else { continue }

                            if geometry["type"] as? String == "LineString" {
                                // Create an array to hold the formatted coordinates for our line

                                if let locations = geometry["coordinates"] as? Array<AnyObject> {
                                    // Iterate over line coordinates,lat arrays

                                    var featureCoordinates = [CLLocationCoordinate2D]()

                                    for location in locations {
                                        // Make a CLLocationCoordinate2D with the lat,lng
                                        if let location = location as? Array<AnyObject>{
                                            let coordinate = CLLocationCoordinate2DMake(location[1].doubleValue,location[0].doubleValue)

                                            // Add coordinate to coordinates array
                                            featureCoordinates.append(coordinate)
                                        }
                                    }

                                    // Uncomment if you need to store for later use.
                                    //self.coordinates.append(featureCoordinates)

                                    DispatchQueue.main.async {
                                        let line = MGLPolyline(coordinates: &featureCoordinates,count: UInt(featureCoordinates.count))

                                        // Optionally set the title of the polyline,which can be used for:
                                        //  - Callout view
                                        //  - Object identification
                                        line.title = "Crema to Council Crest"
                                        self.mapBoxView.addAnnotation(line)

                                    }


                                }

                            }

                        }

                        print("** FINISH **")

                    }

                } catch {
                    print("GeoJSON parsing Failed")
                }
            }
        }
    }
}


func drawSmallListObj(list: [Dictionary<String,AnyObject>]){
    for obj in list{
        //            print(obj)
        if let feature = obj as? Dictionary<String,AnyObject> {
            if let geometry = feature["geometry"] as? Dictionary<String,AnyObject> {
                if geometry["type"] as? String == "LineString" {
                    // Create an array to hold the formatted coordinates for our line
                    var coordinates: [CLLocationCoordinate2D] = []

                    if let locations = geometry["coordinates"] as? Array<AnyObject> {
                        // Iterate over line coordinates,which can be used for:
                    //  - Callout view
                    //  - Object identification
                    line.title = "Crema to Council Crest"

                    // Add the annotation on the main thread
                    DispatchQueue.main.async {
                        // Unowned reference to self to prevent retain cycle
                        [unowned self] in
                        self.mapBoxView.addAnnotation(line)
                    }
                }
            }
        }
    }
}
func mapView(_ mapView: MGLMapView,alphaForShapeAnnotation annotation: MGLShape) -> CGFloat {
    // Set the alpha for all shape annotations to 1 (full opacity)
    return 1
}

func mapView(_ mapView: MGLMapView,lineWidthForPolylineAnnotation annotation: MGLPolyline) -> CGFloat {
    // Set the line width for polyline annotations
    return 2.0
}

func mapView(_ mapView: MGLMapView,strokeColorForShapeAnnotation annotation: MGLShape) -> UIColor {
    // Give our polyline a unique color by checking for its `title` property
    if (annotation.title == "Crema to Council Crest" && annotation is MGLPolyline) {
        // MapBox cyan
        return UIColor(red: 59/255,green:178/255,blue:208/255,alpha:1)
    }
    else
    {
        return UIColor.red
    }
}


}