Most devices provide information about their own location. Each platform has API interfaces on the device that abstract how the location is retrieved, whether through Wi-Fi, cellular networks, or GPS.
Device location can be displayed in the following ways:
- On a map
- As coordinates listed on the screen
Display the location on a map
You can display the current location of the device in a map view by using a location display ().
Optional settings available for a map location display include the following:
- Automatic panning to keep the latest point location visible
- Change of symbol based on the status of the device's location
- Display of metadata, for example the estimated accuracy of the location
- Set the zoom scale of the map in automatic panning or navigation modes
- Set opacity for the symbols used to show location and accuracy
Current location display
By default, the map uses a blue, round symbol to display the device's current location. The map always tries to get the most accurate location available. Depending on signal strength, satellite positions, and other factors, the reported location could be the best approximation. The map displays a blue circle around the location symbol to indicate the range of accuracy.
As the device moves, the map responds to location updates and appropriately updates the location symbol's position.
Location data sources
Location display uses a location data source to provide the current position of the device. By default, location display uses the system's location provider. You can also create custom location data sources to process input from other location providers or to simulate location updates for testing purposes. Stored either in memory or in a file, location updates can be simulated by stepping through a series of points at a predefined time interval.
Permission to access location
Android is a permissions-separated operating system, and you must identify the permissions required by your app in the app manifest (AndroidManifest.xml). With Android 6.0 (API level 23) and later, a user can revoke permissions from any app at any time, even if the app targets a lower API level. If your app used the GPS yesterday, you can't assume the app still has the required ACCESS_FINE_LOCATION permission today and code that uses that functionality may fail.
Therefore if your app is running on Android API level 23 or above, you must explicitly handle permissions (for things like location) at run time by checking for and requesting permissions as you need them. If your app does not have permission to access location, the location display will fail to start and an exception will be thrown. See Runtime Permission Checks in Android 6.0 in the Microsoft documentation for more information and examples.
The Xamarin Android and Xamarin Forms versions of the Display device location sample show how to check for and request the appropriate location permissions from the user.
The map provides a number of presets that define how the map behaves when location updates are received:
- Compass navigation
In this mode, the map only updates the position of the location symbol on the map. It does not recenter. Therefore, it is possible that the location symbol may move off the screen in response to location updates.
In this mode, the map attempts to keep the location symbol on-screen by recentering the location symbol when the symbol moves outside a wander extent. Therefore, the location symbol may move freely within the wander extent, but as soon as the symbol exits the wander extent, the map view pans to recenter itself on the symbol.
By default, the wander extent is half the size of the map's viewable extent, but it can be customized. A value of 1 implies a wander extent equal to the size of the map's viewable extent, and the location symbol may move up to the edge of the map before the map recenters. A value of 0 implies an infinitesimal wander extent, and the map recenters on every location update.
If a user pans the map in this mode, the mode automatically changes its Autopan mode to Off, preventing the map from unwanted recentering based on future location updates.
This mode is best for in-vehicle navigation. In this mode, the location symbol is pinned to a point on the screen and always points toward the top edge of the device. The map pans and rotates based on location updates and the direction the device is traveling in. Therefore, the location symbol appears stationary, while the map underneath it appears to be moving and rotating.
The position of the location symbol can be adjusted. A value of 0 implies the location symbol should be positioned at the bottom edge of the map, and 1 implies the top edge. A value between 0 and 1 positions the symbol somewhere along the centerline from the bottom edge to the top edge.
If a user pans the map in this mode, the mode automatically changes to Off.
Compass Navigation mode
This mode is better when the user is walking. As in Navigation mode, the location symbol is pinned to a point on the screen and always points toward the top edge of the device. However, the map rotates based on the user's bearing relative to magnetic north, and not based on the direction the device travels in, which is the case in Navigation mode. Therefore, the map reflects what lies ahead of the user as the user pivots around their location.
The location symbol position can be adjusted. A value of 0 implies the location symbol should be positioned at the bottom edge of the map, and 1 implies the top edge. A value between 0 and 1 positions the symbol somewhere between the bottom and top edges.
If a user pans the map in this mode, the mode automatically changes to Off.
Customizing the location symbol
The SDK provides default images that are used for the location symbol. These images are resources embedded in the ArcGIS Runtime assembly.
The following properties on LocationDisplay can be changed to use your own symbols.
- AccuracySymbol — fill symbol that illustrates the accuracy of the current location
- AcquiringSymbol — while the location is being acquired
- HeadingSymbol — while in compass navigation mode
- CourseSymbol — when the location is moving; the symbol rotates to show the current heading
- DefaultSymbol — while the location is not moving
Depending on the autopan mode in use, and the type of information provided by the location updates, one of the default images will be used for the location symbol.
In the off, recenter, and navigation modes, the default image is used only when location information is available. The course symbol is used if both location information and course (direction of travel) information are available. In the off and recenter modes, the course symbol is appropriately rotated by an amount specified by the course to display the direction in which the device is traveling; however, in Navigation mode, the map rotates instead.
Course information is only available when the device is moving at some nontrivial velocity. This is why the map typically only displays the course symbol when the device is traveling in a vehicle.
In the Compass Navigation mode, the heading image is used to display the device's location and bearing.
Displaying the location as coordinates on the screen
Maps are not always the focus of your application, yet device location can still matter. You may require location to populate fields in a form, display the current coordinates on the screen, or show a scrolling list of coordinates to represent movement. When coordinates are displayed on the screen, you can use the color, size, or font of the text to convey additional information. However currently, the location display is only available from a map view.