iphone - 如何检测 MKMapView 是否缩小/缩小？

Question

我正在编写以下代码，

- (void)mapView:(MKMapView *)mapView regionWillChangeAnimated:(BOOL)animated {
    mapRegion = mapView.region; //MKCoordinateRegion myRegion in .h
}

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

      MKCoordinateRegion newRegion = mapView.region;

    if (mapRegion.span.latitudeDelta != newRegion.span.latitudeDelta ||
       mapRegion.span.longitudeDelta != newRegion.span.longitudeDelta){

        NSLog(@"The zoom has changed");        
  }
}

当用户放大或缩小 MKMapView 时，我想执行一些操作，我应该做什么，但是通过应用上面的代码，如果条件将执行，则使用不会放大/缩小，但只会更改 map ？

Answer 1

创建MKMapView+ZoomLevel.h为

#import <MapKit/MapKit.h>

@interface MKMapView (ZoomLevel)

- (void)setCenterCoordinate:(CLLocationCoordinate2D)centerCoordinate
                  zoomLevel:(double)zoomLevel
                   animated:(BOOL)animated;

@end 

创建MKMapView+ZoomLevel.m为

#import "MKMapView+ZoomLevel.h"

#define MERCATOR_OFFSET 268435456
#define MERCATOR_RADIUS 85445659.44705395

@implementation MKMapView (ZoomLevel)

#pragma mark -
#pragma mark Map conversion methods

- (double)longitudeToPixelSpaceX:(double)longitude
{
    return round(MERCATOR_OFFSET + MERCATOR_RADIUS * longitude * M_PI / 180.0);
}

- (double)latitudeToPixelSpaceY:(double)latitude
{
    return round(MERCATOR_OFFSET - MERCATOR_RADIUS * logf((1 + sinf(latitude * M_PI / 180.0)) / (1 - sinf(latitude * M_PI / 180.0))) / 2.0);
}

- (double)pixelSpaceXToLongitude:(double)pixelX
{
    return ((round(pixelX) - MERCATOR_OFFSET) / MERCATOR_RADIUS) * 180.0 / M_PI;
}

- (double)pixelSpaceYToLatitude:(double)pixelY
{
    return (M_PI / 2.0 - 2.0 * atan(exp((round(pixelY) - MERCATOR_OFFSET) / MERCATOR_RADIUS))) * 180.0 / M_PI;
}

#pragma mark -
#pragma mark Helper methods

- (MKCoordinateSpan)coordinateSpanWithMapView:(MKMapView *)mapView
                             centerCoordinate:(CLLocationCoordinate2D)centerCoordinate
                                 andZoomLevel:(double)zoomLevel
{
    NSLog(@"in custom zoomlevel-->%f",zoomLevel);
    // convert center coordiate to pixel space
    double centerPixelX = [self longitudeToPixelSpaceX:centerCoordinate.longitude];
    double centerPixelY = [self latitudeToPixelSpaceY:centerCoordinate.latitude];

    // determine the scale value from the zoom level
    double zoomExponent = 20.0 - zoomLevel;
    double zoomScale = pow(2, zoomExponent);

    // scale the map’s size in pixel space
    CGSize mapSizeInPixels = mapView.bounds.size;
    double scaledMapWidth = mapSizeInPixels.width * zoomScale;
    double scaledMapHeight = mapSizeInPixels.height * zoomScale;

    // figure out the position of the top-left pixel
    double topLeftPixelX = centerPixelX - (scaledMapWidth / 2);
    double topLeftPixelY = centerPixelY - (scaledMapHeight / 2);

    // find delta between left and right longitudes
    CLLocationDegrees minLng = [self pixelSpaceXToLongitude:topLeftPixelX];
    CLLocationDegrees maxLng = [self pixelSpaceXToLongitude:topLeftPixelX + scaledMapWidth];
    CLLocationDegrees longitudeDelta = maxLng - minLng;

    // find delta between top and bottom latitudes
    CLLocationDegrees minLat = [self pixelSpaceYToLatitude:topLeftPixelY];
    CLLocationDegrees maxLat = [self pixelSpaceYToLatitude:topLeftPixelY + scaledMapHeight];
    CLLocationDegrees latitudeDelta = -1 * (maxLat - minLat);

    // create and return the lat/lng span
    MKCoordinateSpan span = MKCoordinateSpanMake(latitudeDelta, longitudeDelta);
    return span;
}

#pragma mark -
#pragma mark Public methods

- (void)setCenterCoordinate:(CLLocationCoordinate2D)centerCoordinate
                  zoomLevel:(double)zoomLevel
                   animated:(BOOL)animated
{
    // clamp large numbers to 28
    zoomLevel = MIN(zoomLevel, 28);

    // use the zoom level to compute the region
    MKCoordinateSpan span = [self coordinateSpanWithMapView:self centerCoordinate:centerCoordinate andZoomLevel:zoomLevel];
    MKCoordinateRegion region = MKCoordinateRegionMake(centerCoordinate, span);

    // set the region like normal
    [self setRegion:region animated:animated];
}

@end 

#import "MKMapView+ZoomLevel.h" 在 View Controller 中使用 MKMapView 的语句。

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated
{   
    double zoomLevel = [self getZoomLevel]; 
    [lblCurrentLevel setText:[NSString stringWithFormat:@"%.2f",zoomLevel]];

    NSLog(@"zoomlevel-->%f long-->%f lat-->%f",zoomLevel,mapView.region.span.longitudeDelta,mapView.region.span.latitudeDelta);
}

- (double) getZoomLevel
{
    return 21.00 - log2(objMapView.region.span.longitudeDelta * MERCATOR_RADIUS * M_PI / (180.0 * objMapView.bounds.size.width));
}

在上述方法中，您可以根据需要获得缩放级别，您唯一要做的就是保持初始缩放并将最新的放大/缩小与该缩放进行比较，然后再次分配给该变量。

如果有任何疑问，请告诉我，我们会解决这个问题:D

编辑

此源代码来自Troy's博客。抱歉之前没有提及。