Navigating the map
The Map View includes options for defining and changing the map extent as well as the user experience when the extent is modified. It is important to note that the basmap layer (the first layer added to the map) will define the follow properties for the map:
- Initial extent
- Full extent
- Spatial reference
While initial extent can be modified, the spatial reference cannot be changed explicitly. This document will discuss both developer and end-user solutions for working with map extent.
Setting the map extent
To set the map extent, use the zoomToEnvelope:animated: method on the map view by passing in an evelope geometry representing the area you want to zoom to.
-(void)viewDidLoad{
[super viewDidLoad];
//add a layer to the map
AGSTiledMapServiceLayer*tiledLayer=[AGSTiledMapServiceLayer tiledMapServiceLayerWithURL:[NSURLURLWithString:@"http://server.arcgisonline.com/ArcGIS/rest/services/ESRI_StreetMap_World_2D/MapServer"]];
[self.mapViewaddMapLayer:tiledLayerwithName:@"Tiled Layer"];
//zoom to an area
AGSEnvelope *envelope = [AGSEnvelope envelopeWithXmin:-124.83145667 ymin:30.49849464 xmax:-113.91375495 ymax:44.69150688 spatialReference:mapView.spatialReference];
[self.mapView zoomToEnvelope:envelope animated:NO];
}
![Note Note](rsrc/note.png)
The envelope or geometry you use to zoom the map must have the same spatial reference as that of the map.
Getting the map extent
You may not know the extent of the map until runtime. You can use the visibleArea property of the map view to get the extent of the map.
AGSEnvelope* mapExtent = self.mapView.visibleArea;
The map view must have been loaded for the visibleArea property to be valid.
Tracking panning and zooming
The map view provides two notifications for extent changes, MapDidEndPanning and MapDidEndZooming. These notifications are broadcast after the map has been panned or zoomed, respectively. The following code is an example of how to listen for notifications when the user pans or zooms the map. It displays an alert showing the new map extent retrieved from the envelope property of the map view:
- (void)mapViewDidLoad:(AGSMapView *)mapView {
// register for "MapDidEndPanning" notifications
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(respondToEnvChange:)
name:@"MapDidEndPanning" object:nil];
// register for "MapDidEndZooming" notifications
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(respondToEnvChange:)
name:@"MapDidEndZooming" object:nil];
...
}
// The method that should be called when the notification arises
- (void)respondToEnvChange: (NSNotification*) notification {
//create the string containing the new map extent NSString*
NSString* theString = [[NSString alloc] initWithFormat:@"xmin = %f,\nymin =
%f,\nxmax = %f,\nymax = %f", mapView.envelope.xmin,
mapView.envelope.ymin, mapView.envelope.xmax,
mapView.envelope.ymax];
//display the new map extent in a simple alert
UIAlertView* alertView = [[UIAlertView alloc] initWithTitle:@"mapViewDidEndPanning"
message:theString delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alertView show];
[alertView release];
[theString release];
}
You should note that these notifications are broadcast when the processor is idle, thus there might be a slight delay between when the user finished performing the action and when the notification was raised. Also, notificatons are delievered on the main thread. You should not block this thread by pefroming expensive tasks otherwise your application will appear sluggish to the user.
Changing the map extent
As mentioned previously, you can use the zoomToEnvelope:animated: method on a map view to set a map view's extent. You can also center the map at a given point using the map view's centerAtPoint:animated: method:
AGSPoint *newPoint = [AGSPoint pointWithX:-93.032201 y:49.636213 spatialReference:self.mapView.spatialReference];
[self.mapView centerAtPoint:newPoint animated:NO];
User gestures
The user can perform several gestures which change the map view's extent at run-time. All of these will trigger either the MapDidEndPanning and MapDidEndZooming notifications.
User Action | Map Action | Notification raised |
---|---|---|
Pinch-In | Zoom out on map | MapDidEndZooming |
Pinch-Out | Zoom in on map | MapDidEndZooming |
Double Tap | Zoom in on map | MapDidEndZooming |
Two finger Tap | Zoom out on map | MapDidEndZooming |
Swipe (any direction) | Pan map in direction of swipe | MapDidEndPanning |
Two finger Twist* | Rotate the map |
![Note Note](rsrc/note.png)
You must enable the allowRotationByPinching property on AGSMapView to enable the Two finger Twist gesture.