来自geocodeAddressString的意外结果

Question

我的问题是，当addressTF.text有一个非常合理的地址字符串时，为什么poiCoordinate的纬度和经度属性会出现0,0，例如“1 Infinite Loop，Cupertino，CA 95014”？

//HomeViewController.m

@implementation HomeViewController

CLLocationCoordinate2D poiCoordinate;

-(void)performStringGeocode
{
    CLGeocoder *geocoder = [[CLGeocoder alloc] init];
    [geocoder geocodeAddressString:_addressTF.text completionHandler:^(NSArray *placemarks, NSError *error)
    {
        if (error)
        {
            NSLog(@"Geocode failed with error: %@", error);
            return;
        }
    CLPlacemark *placemark = [placemarks firstObject]; //Line A
    poiCoordinate = placemark.location.coordinate;     //Line B
    }];
}