使用 URLWithString 调用 Google 地图时获取“路线不可用”

Question

我有一个应用程序非常成功地使用了 Apple 地图：我有一个包含一些兴趣点的列表，如果我先点击其中一个，应用程序会在地图上显示它，然后，如果我点击它，它会打开 Apple 地图应用导航。

问题是，在第一次点击/启动时，应用程序会打开 Apple Maps，但无论是否请求使用用户位置的权限，Apple Maps 都不起作用并返回：“Directions Not Available . 在这些位置之间找不到方向。”但在 General Setting 中，我的应用的位置服务设置为 ON。

我认为我必须使用某种超时，因为我的应用程序需要很长时间来解析导航数据（我从 xml 检索数据）但在第二次点击时一切正常，即使我从 Mac 中运行它调试模式（甚至第二次解析xml）...

我希望我解释得很好。有什么提示吗？

   -(MKAnnotationView *)mapView:(MKMapView *)mV viewForAnnotation:(id <MKAnnotation>)annotation 
{
    MKPinAnnotationView *pinView = nil; 
    if(annotation != mapView.userLocation) 
    {
    static NSString *defaultPinID = @"com.invasivecode.pin";
    pinView = (MKPinAnnotationView *)[mapView dequeueReusableAnnotationViewWithIdentifier:defaultPinID];
    if ( pinView == nil ) pinView = [[[MKPinAnnotationView alloc]
                                      initWithAnnotation:annotation reuseIdentifier:defaultPinID] autorelease];

    pinView.pinColor = MKPinAnnotationColorRed; 


    UIButton *myAccessoryButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 24, 24)];
    [myAccessoryButton setBackgroundColor:[UIColor clearColor]];
    [myAccessoryButton setImage:[UIImage imageNamed:@"flag.png"] forState:UIControlStateNormal];
    pinView.rightCalloutAccessoryView = myAccessoryButton;
    pinView.canShowCallout = YES;
    pinView.animatesDrop = YES;
    [myAccessoryButton release];
} 
else {
    [mapView.userLocation setTitle:@"You're here"];
}
return pinView;
}

-(void)mapView:(MKMapView *)mapView annotationView:(MKAnnotationView *)view calloutAccessoryControlTapped:(UIControl *)control{

locationManager = [[CLLocationManager alloc] init];
locationManager.delegate = self; 
locationManager.desiredAccuracy = kCLLocationAccuracyBest; 
locationManager.distanceFilter = kCLDistanceFilterNone; 
[locationManager startUpdatingLocation];

CLLocation *location = [locationManager location];

// Configure the new event with information from the location
CLLocationCoordinate2D coordinate = [location coordinate];

NSString *latitude = [NSString stringWithFormat:@"%f", coordinate.latitude]; 
NSString *longitude = [NSString stringWithFormat:@"%f", coordinate.longitude];


CLLocationCoordinate2D start = { [latitude floatValue], [longitude floatValue] };
CLLocationCoordinate2D end = {[posto.latitude floatValue], [posto.longitude floatValue]};

NSString *googleMapsURLString = [NSString stringWithFormat:@"http://maps.google.com/?saddr=%1.6f,%1.6f&daddr=%1.6f,%1.6f", start.latitude, start.longitude, end.latitude, end.longitude];

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:googleMapsURLString]];
}

Answer 1

在calloutAccessoryControlTapped 中，您在调用startUpdatingLocation 后立即使用[locationManager location]。

location 通常在开始查找当前位置后立即不可用（如果是，它可能不可靠或已过时）。

当location 可用时，位置管理器将调用其didUpdateToLocation 委托方法，这就是您应该移动startUpdatingLocation 之后的所有代码的地方。

（即使在那个委托方法中，在使用它之前检查newLocation 是否是nil 可能是个好主意。有时在地图视图等待用户授予位置服务权限时会发生这种情况（见this question))。

-(void)mapView:(MKMapView *)mapView annotationView:(MKAnnotationView *)view calloutAccessoryControlTapped:(UIControl *)control
{
    locationManager = [[CLLocationManager alloc] init];
    locationManager.delegate = self; 
    locationManager.desiredAccuracy = kCLLocationAccuracyBest; 
    locationManager.distanceFilter = kCLDistanceFilterNone; 
    [locationManager startUpdatingLocation];
}

-(void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    if (newLocation == nil)
    {
        NSLog(@"didUpdateToLocation: newLocation is nil");
        return;
    }

    //May want to check newLocation.horizontalAccuracy and 
    //newLocation.timestamp to see if the location is accurate 
    //enough for you.  If not, return and wait for a more 
    //accurate location (which may never come).

    //all the code currently after "startUpdatingLocation" goes here...
    CLLocation *location = [locationManager location];
    ...
}

-(void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
    NSLog(@"locationManager:didFailWithError: %@", error);
}

您可能还想实现didFailWithError 来处理获取位置的任何问题，或者至少知道它。