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A Helper Class to Get the Current Location on a Windows Phone Just Once

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15 Jan 2011CPOL 28.2K   6   14
Here is a helper class to get the current location on a Windows Phone just once

Getting the location on Windows Phone is done via the GeoCoordinateWatcher. The coordinate watcher has some best practices associated with it one of which is to minimize power consumption. Once you turn this thing on, it's going to be using the GPS to stream location event back to your app which will hit the battery.

There are some instances where you may note a running notification of the current portion but just want the current position (for instance, you may want to initialize the position on a map but not track changes to position).

So this is a small helper class that starts up the coordinate watcher asynchronously, returns the first coordinate found and then shuts it down. One could use TryStart like so:

C#
using (var watcher =  new 
                GeoCoordinateWatcher(GeoPositionAccuracy.Default))
{
    var location = watcher.TryStart
                (false, TimeSpan.FromMilliseconds(1000));
}

but since that will block your UI thread (assuming you call it from the UI) you'd need to wrap it in some asynchronous stuff anyways.
So I use this class:

C#
public class ImmediateLocation : IDisposable
{
    private GeoCoordinateWatcher _watcher;
    private Action<GeoCoordinate> _action;

    public ImmediateLocation(Action<GeoCoordinate> a)
    {
        Debug.Assert(a != null);

        _action = a;
    }

    public void GetLocation()
    {
        if (_watcher == null)
        {
            _watcher = new GeoCoordinateWatcher(GeoPositionAccuracy.Default);
            _watcher.MovementThreshold = 1000;

            _watcher.PositionChanged += new 
                EventHandler<GeoPositionChangedEventArgs<GeoCoordinate>>
                (_watcher_PositionChanged);
            _watcher.StatusChanged += new 
                EventHandler<GeoPositionStatusChangedEventArgs>
                (_watcher_StatusChanged);

            _watcher.Start(false);

            if (_watcher.Status == GeoPositionStatus.Disabled
                || _watcher.Permission == GeoPositionPermission.Denied)
                Dispose();
        }
    }

    void _watcher_StatusChanged(object sender, 
        GeoPositionStatusChangedEventArgs e)
    {
        if (e.Status == GeoPositionStatus.Disabled 
            || _watcher.Permission == GeoPositionPermission.Denied)
            Dispose();
    }

    void _watcher_PositionChanged(object sender, 
        GeoPositionChangedEventArgs<GeoCoordinate> e)
    {
        _action(e.Position.Location);
        Dispose();
    }

    public void Dispose()
    {
        if (_watcher != null)
        {
            _watcher.Stop();
            _watcher.PositionChanged -= new 
                EventHandler<GeoPositionChangedEventArgs<GeoCoordinate>>
                (_watcher_PositionChanged);
            _watcher.StatusChanged -= new 
                EventHandler<GeoPositionStatusChangedEventArgs>
                (_watcher_StatusChanged);
            _watcher.Dispose();
        }
        _watcher = null;
        _action = null;
    }
} 

Then you can just do this:

C#
var immediate = new ImmediateLocation(x => location = x);
immediate.GetLocation();

GeoCoordinate location;

It acts like a one time use, fire and forget location setter that cleans itself up when done. It does have Dispose if you want to manage the lifetime more closely.

This article was originally posted at http://spookycoding.blogspot.com/feeds/posts/default

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Team Leader Starkey Laboratories
United States United States
The first computer program I ever wrote was in BASIC on a TRS-80 Model I and it looked something like:
10 PRINT "Don is cool"
20 GOTO 10

It only went downhill from there.

Hey look, I've got a blog

Comments and Discussions

 
QuestionHow to get the location? Pin
Saggaf Arsyad16-Dec-12 21:06
Saggaf Arsyad16-Dec-12 21:06 
GeneralMy vote of 5 Pin
Colin Eberhardt24-Nov-12 8:21
Colin Eberhardt24-Nov-12 8:21 
QuestionHow to consume result / battery tradeoff of start/dispose vs leave it running / accuracy control Pin
Member 459906229-Aug-12 0:47
Member 459906229-Aug-12 0:47 
AnswerRe: How to consume result / battery tradeoff of start/dispose vs leave it running / accuracy control Pin
Don Kackman29-Aug-12 9:52
Don Kackman29-Aug-12 9:52 
QuestionRe: How to consume result / battery tradeoff of start/dispose vs leave it running / accuracy control Pin
Member 459906229-Aug-12 10:46
Member 459906229-Aug-12 10:46 
GeneralThe code always returns a null on a real WP7 Pin
Orrin4-Mar-11 19:21
Orrin4-Mar-11 19:21 
Hi there,
I finally got back to trying to use this code. I suggest that the reason for the return null is that, when using an actual WP7, after calling GetLocation(), the execution is returned to the calling code before the event handler _watcher_PositionChanged is called.
Hence the calling code always sees a null. Do you have any suggestions other than to incorporate the code dependent on location
in the _watcher_PositionChanged event handler?
Thanks,
docorrin
GeneralAlways returns a null Pin
Orrin15-Jan-11 9:28
Orrin15-Jan-11 9:28 
GeneralAlways returns a null Pin
Orrin15-Jan-11 8:49
Orrin15-Jan-11 8:49 
GeneralRe: Always returns a null Pin
Don Kackman15-Jan-11 9:02
Don Kackman15-Jan-11 9:02 
GeneralRe: Always returns a null Pin
Don Kackman15-Jan-11 9:04
Don Kackman15-Jan-11 9:04 
GeneralRe: Always returns a null Pin
Orrin15-Jan-11 10:48
Orrin15-Jan-11 10:48 
GeneralRe: Always returns a null Pin
Don Kackman15-Jan-11 12:32
Don Kackman15-Jan-11 12:32 
GeneralRe: Always returns a null Pin
Orrin15-Jan-11 12:53
Orrin15-Jan-11 12:53 
GeneralMy vote of 5 Pin
maq_rohit9-Dec-10 21:59
professionalmaq_rohit9-Dec-10 21:59 

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