Plotting current position on the Map control in Windows Phone

Comments

Hamishwillee - Subedited

Hi Somnath

I've subedited this. Remember its important to add references to key articles on MSDN (now done). Also you will rarely need "basic idea" section - just put that as part of the introduction.

I don't really understand this code - can you explain?

            gcw.StatusChanged += new EventHandler<GeoPositionStatusChangedEventArgs>(gcw_StatusChanged);
            gcw.PositionChanged += new EventHandler<GeoPositionChangedEventArgs<GeoCoordinate>>(gcw_PositionChanged);
            gcw.Start();
            map1.Center = new GeoCoordinate(gcw.Position.Location.Latitude, gcw.Position.Location.Longitude);

Specifically, you seem to be defining an event handler gcw_StatusChanged but this isn't being called anywhere. Also, you Start() the gcw then immediately use its position in the map1.Center. How do you know that the value isn't Null at this point.

What I think is happening is that you're defining event handlers that you don't use. The person presses the menu a few times and eventually the position will be populated with a value, before this nothing happens. If I'm right then a better implementation would be to set the map center in the event handler - then if they press the button they just need to wait until a position is retrieved. Make sense?

Regards

H

hamishwillee 07:28, 27 April 2012 (EEST)

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This article demonstrates how to zoom to a user's position on a Map Control based on location information from the GeoCoordinateWatcher class.

See Also

• How to: Get Data from the Location Service for Windows Phone (MSDN)
• Location for Windows Phone (MSDN)
• Location Programming Best Practices for Windows Phone (MSDN
  • GeoCoordinateWatcher best practice questions (social.msdn)
• Maps Examples for Windows phone
• Windows Phone GPS Emulator (developer blog)

Article Metadata

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Code Example

Source file: Media:MapControls.zip

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Tested with

SDK: Windows Phone SDK 7.1

Devices(s): WP7 Emulator

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Compatibility

Platform(s): Windows Phone 7.5

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Article

Keywords: Map Controls/GeoCoordinateWatcher

Created: somnathbanik (14 Oct 2011)

Last edited: hamishwillee (30 Nov 2012)

Introduction

This example app creates a Map. When a user clicks on the my location menu, the app fetches the current location of the device and put the latitude and longitude in the Map in zoom view. The current location is retrieved using the GeoCoordinateWatcher class (from the System.Device.Location namespace).

Current Location

Implementation

First create a project with Windows Phone Application Template.

Create map (MainPage.xaml)

Once the project is created, drag and drop a new Map control onto the page from the Visual Studio 2010 Toolbox. This will generate the Map Control code in the XAML file.

<my:Map Height="408" HorizontalAlignment="Left" Margin="6,20,0,0" Name="map1" VerticalAlignment="Top" Width="444" Mode="AerialWithLabels" CredentialsProvider="{StaticResource BingMapsAPIKey}" >
</my:Map>

To use the map you need to get a Bing maps key, which can be obtained from http://www.bingmapsportal.com/. You can replace the {StaticResource BingMapsAPIKey} with your key (as shown below):

<my:Map Height="408" HorizontalAlignment="Left" Margin="6,20,0,0" Name="map1" VerticalAlignment="Top" Width="444" Mode="AerialWithLabels" CredentialsProvider="Anqep9VR0k6VxcmRp4qJ_AYWglilkC3B4c2QgZAgZTBS-bCr2GOI7iOopDGd-PXa" >
</my:Map>

Alternatively you can declare the BingMapsAPIKey static resource in your App.xaml file - note that this is recommended if you're planning on using the key anywhere else in the app.

<Application.Resources>
        <my:ApplicationIdCredentialsProvider ApplicationId="Anqep9VR0k6VxcmRp4qJ_AYWglilkC3B4c2QgZAgZTBS-bCr2GOI7iOopDGd-PXa" x:Key="BingMapsAPIKey"></my:ApplicationIdCredentialsProvider>
    </Application.Resources>

Get co-ordinates and zoom

Now we add the Menu with the name My Location. When user clicks on the menu it calls ApplicationBarMenuItem_Click(), which in turn has the code to get the location.

private void ApplicationBarMenuItem_Click(object sender, EventArgs e)
        {
            GeoCoordinateWatcher gcw;
            gcw = new GeoCoordinateWatcher(GeoPositionAccuracy.High);
            gcw.MovementThreshold = 20;
            gcw.StatusChanged += new EventHandler<GeoPositionStatusChangedEventArgs>(gcw_StatusChanged);
            gcw.PositionChanged += new EventHandler<GeoPositionChangedEventArgs<GeoCoordinate>>(gcw_PositionChanged);
            gcw.Start();
            map1.Center = new GeoCoordinate(gcw.Position.Location.Latitude, gcw.Position.Location.Longitude);
            if (gcw != null) gcw.Stop();
            map1.ZoomLevel = 17;
            map1.ZoomBarVisibility = Visibility.Visible;
            map1.ScaleVisibility = Visibility.Visible;
        }

We create an instance of GeoCoordinateWatcher and set the accuracy to High and threshold value to 20 which is approx 20 meters around. Event GeoPositionStatusChangedEventArgs gets the updated Status and GeoPositionChangedEventArgs event gets the location data associated with the event, like the latitude and longitude. Start() method enables PositionChanged events and allows access to the Position property. Once we get this data we put the value in the map and display the location in map’s center position. And finally Stops the GeoCoordinateWatcher from providing location data and events with Stop() method. We also set the zoom level property of the map.

Testing

This application has only been tested on emulator. The articles below discuss how to test maps on the emulator:

• Windows Phone GPS Emulator
• this.

Source Code

The full source code of the example is available here: File:MapControls.zip