如何比較兩個不同的地圖視圖區域，並找出它們之間的區別

Question

嗨，我是開發Map-view Base應用程序的人。我差不多已經完成了所有的map-view，但我無法比較兩個不同的地圖視圖區域並找到新的地圖視圖區域。例如，如果用戶拖動地圖，我想查找該地區發生了多大變化。

Answer 1

這個答案告訴你如何比較兩個地圖點。你可以在地圖區域的中心使用它：link。

Answer 2

首先你需要找到初始地圖區域。說你的地圖被命名爲MapView的......你可以先通過（在viewDidLoad中）找到此：

CLLocationCoordinate2D center = mapView.centerCoordinate; 
CLLocationDegrees lat = center.latitude; 
CLLocationDegrees lon = center.longitude; 

MKCoordinateRegion region = mapView.region; 
MKCoordinateSpan span = region.span; 

//Assuming they have been declared as instance variables of type double 
current_lat_low = lat - span.latitudeDelta/2.0; 
current_lat_high = lat + span.latitudeDelta/2.0; 
current_lon_low = lon - span.longitudeDelta/2.0; 
current_lon_high = lon + span.longitudeDelta/2.0; 

這會給你顯示的地圖的初始區域。然後在

- (void)mapView:(MKMapView*)mapView regionDidChangeAnimated:(BOOL)animated 
{ 

    CLLocationCoordinate2D center = mapView.centerCoordinate; 
    CLLocationDegrees lat = center.latitude; 
    CLLocationDegrees lon = center.longitude; 

    MKCoordinateRegion region = mapView.region; 
    MKCoordinateSpan span = region.span; 

    double lat_low = lat - span.latitudeDelta/2.0; 
    double lat_high = lat + span.latitudeDelta/2.0; 
    double lon_low = lon - span.longitudeDelta/2.0; 
    double lon_high = lon + span.longitudeDelta/2.0; 

    //do any work comparing the initial lat/lons with the new values 
    ..... 

    //set current lat/lon to be the new lat/lon after work is complete 
    current_lat_low = lat_low; 
    current_lat_high = lat_high; 
    current_lon_low = lon_low; 
    current_lon_high = lon_high; 
}