海神

定位用到CoreLocation库，添加一个CLLocationManager，然后实现CLLocationManagerDelegate协议，初始化CLLocationManager的方法：

- (void) viewDidLoad {
lm = [[CLLocationManager alloc] init];
if ([lm locationServicesEnabled]) {
lm.delegate = self;
lm.desiredAccuracy = kCLLocationAccuracyBest;
lm.distanceFilter = 1000.0f;
[lm startUpdatingLocation];
}
}

desiredAccuracy指定定位的精度，distanceFilter表示移动多少米才会更新。 然后在两个事件中处理位置信息：

locationManager:didUpdateToLocation:fromLocation: locationManager:didFailWithError:

- (void) locationManager: (CLLocationManager *) manager didUpdateToLocation: (CLLocation *) newLocation  fromLocation: (CLLocation *) oldLocation{
NSString *lat = [[NSString alloc] initWithFormat:@"%g",
newLocation.coordinate.latitude];
latitudeTextField.text = lat;

NSString *lng = [[NSString alloc] initWithFormat:@"%g",
newLocation.coordinate.longitude];
longitudeTextField.text = lng;

NSString *acc = [[NSString alloc] initWithFormat:@"%g",
newLocation.horizontalAccuracy];
accuracyTextField.text = acc;

[acc release];
[lat release];
[lng release];
}

latitude是经度，longitude是纬度，horizontalAccuracy是精确度，单位是米。

显示地图需要用到MapKit库。初始化：

mapView = [[MKMapView alloc] initWithFrame:self.view.bounds];
mapView.mapType = MKMapTypeHybrid;

mapType代表地图的类型，是卫星图或者是普通地图

显示地图：

MKCoordinateSpan span;
span.latitudeDelta = .005;
span.longitudeDelta = .005;
MKCoordinateRegion region;
region.center = newLocation.coordinate;
region.span = span;
[self.mapView setRegion:region animated:YES];
CLLocationCoordinate2D coords = {newLocation.coordinate.latitude, newLocation.coordinate.longitude};
MyAnnotation *mk = [[MyAnnotation alloc] initWithCoordinate:coords title:@"我家" subTitle:@"地址"];
[self.mapView addAnnotation: mk]; 
[mk release];
[self.mapView selectAnnotation:mk animated:YES];

MKCoordinateRegion用来指定地图显示的位置和大小，MKCoordinateSpan表示显示的经纬度的跨度。

MyAnnotation是实现MKAnnotation的一个类，表示地图上的一个图钉，title和subTitle是显示在图钉旁边的文字。