Google Maps IOS SDK展开时意外为零调用当前位置时可选

我在使用Google Maps IOS SDK时遇到问题。当我尝试调用一个当前位置时，我得到了错误“unexpected nil When unwrapping optional”。当引用newLocation变量时，我似乎得到了nil。任何帮助都将不胜感激

import UIKit;
import GoogleMaps;
import CoreLocation;


class GoHomeController: UIViewController, CLLocationManagerDelegate{
@IBOutlet weak var mapView: GMSMapView! //View holding google map in main.storyboard

private var locationManager = CLLocationManager();

override func viewDidLoad() {
    super.viewDidLoad();
    let mapview = GMSMapView.mapWithFrame(CGRectZero, camera: GMSCameraPosition.cameraWithLatitude(35, longitude: -65, zoom: 10.0));
    locationManager.delegate = self;
    locationManager.requestAlwaysAuthorization();
    self.locationManager.desiredAccuracy = kCLLocationAccuracyBest;
    self.locationManager.startUpdatingLocation();
    mapview.myLocationEnabled = true;
    mapView = mapview;


}
func locationManager(manager: CLLocationManager!, didFailWithError error: NSError!) {
    print("didFailWithError: \(error.description)");
    let errorAlert = UIAlertView(title: "Error", message: "Failed to Get Your Location", delegate: nil,cancelButtonTitle: "Ok");
    errorAlert.show();
}
func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
    let newLocation = locations.last as CLLocation!
    //print("current position: \(newLocation.coordinate.longitude) , \(newLocation.coordinate.latitude)")
    if let location = newLocation{
    updateMapFrame(location, zoom: 10.0);
    }
    }
func updateMapFrame(newLocation: CLLocation, zoom: Float) {
    let camera = GMSCameraPosition.cameraWithTarget(newLocation.coordinate, zoom: zoom)
    self.mapView.animateToCameraPosition(camera) // Error occurs here
}


}

谢谢大家抽出时间

编辑：我忘了提到GoHomeController只是我项目中的视图控制器。这不是主要的，我有一段通向它的路

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编辑#2：在模拟器中启动应用程序后，当我进入回家场景时，就会发生错误。

这是一个众所周知的问题。在Xcode to Edit Scheme->Disable Metal Api将解决此问题。

在哪行代码上出现错误？在updateMapFrame函数中的self.mapView.animateToCameraPosition（camera）。嘿，谢谢你的回答。我进入产品->编辑方案->我的项目。但是，一旦到了那里，我就找不到禁用金属api的选项。@在“选项”选项卡下的“运行”按钮-->产品名称->编辑方案->金属api验证设置为“禁用”