Gath Adams

So you’ve been checking out my previous posts on Google Maps and Draggable Markers, and it would be nice to have a demo so you can see the draggable markers in action.

Check this out:

And the code as well? Here is the source for the Google Maps Demo

Following on from my last post on how to add Google Maps to your ASP.Net site, I’m now going to show how easy it is to add draggable markers to your map.

First, make sure you have the map working on your webform.

Having the map fire server-side events on user actions is pretty simple, and here is the code:

    Private Sub AddEventToMapDemo()
        Dim GeoCode As Subgurim.Controles.GeoCode
        Dim sMapKey As String = System.Configuration.ConfigurationManager.AppSettings("googlemaps.subgurim.net")

        GeoCode = GMap.geoCodeRequest("3052. VIC. australia", sMapKey)
        Dim gLatLng As New Subgurim.Controles.GLatLng(GeoCode.Placemark.coordinates.lat, GeoCode.Placemark.coordinates.lng)

        GMap.setCenter(gLatLng, 16, Subgurim.Controles.GMapType.GTypes.Normal)
        Dim oOption As New Subgurim.Controles.GMarkerOptions
        oOption.draggable = True
        oMarker = New Subgurim.Controles.GMarker(gLatLng, oOption)
        GMap.addGMarker(oMarker)

        GMap.addListener(New Subgurim.Controles.GListener(oMarker.ID, Subgurim.Controles.GListener.Event.dragend, _
        "function(){{ var ev = new serverEvent('dragend', 0); ev.addArg(" & oMarker.ID & ".getPoint().lat()); ev.addArg(" & oMarker.ID & ".getPoint().lng()); ev.send(); }}"))

    End Sub

You then need to add code to handle the event:

    Protected Function GMap_ServerEvent(ByVal s As Object, ByVal e As Subgurim.Controles.GAjaxServerEventOtherArgs) As String

        If e.eventName = "dragend" Then
            Response.Write("New Latitude =" & e.eventArgs(0) & ", New Longitude = " & e.eventArgs(1))
        End If

    End Function

The server-side event will be fired every time the marker is dragged and dropped.

In my situation, I wanted to allow the user to drag & drop the marker as many times as they wanted - and only store the new Lat/Long values when the user pressed the Save button.

This is a little bit harder to code as the variables used to reference the marker cannot be accessed globally - so we can’t just read their values when the user presses the save button (to the gurus: I’m sure they can, but I couldn’t find an easy way to get at them) . However, we can store them in hidden fields when the DragEnd event is raised, and examine those fields when Save is pressed.

Add these fields to your webform:

<input type=hidden id="hidLat" name="hidLat" runat=server />
<input type=hidden id="hidLng" name="hidLng" runat=server />
<asp:Button ID="Button1" runat="server" Text="Save" />

And add this sub to your code-behind:

    Private Sub NewLatLongOnSaveMapDemo()
        Dim GeoCode As Subgurim.Controles.GeoCode
        Dim sMapKey As String = System.Configuration.ConfigurationManager.AppSettings("googlemaps.subgurim.net")

        GeoCode = GMap.geoCodeRequest("3052. VIC. australia", sMapKey)
        Dim gLatLng As New Subgurim.Controles.GLatLng(GeoCode.Placemark.coordinates.lat, GeoCode.Placemark.coordinates.lng)

        GMap.setCenter(gLatLng, 16, Subgurim.Controles.GMapType.GTypes.Normal)
        Dim oOption As New Subgurim.Controles.GMarkerOptions
        oOption.draggable = True
        oMarker = New Subgurim.Controles.GMarker(gLatLng, oOption)
        GMap.addGMarker(oMarker)

            GMap.addListener(New Subgurim.Controles.GListener(oMarker.ID, Subgurim.Controles.GListener.Event.dragend, _
            "function(){ document.getElementById('hidLat').value=" & oMarker.ID & ".getPoint().lat();document.getElementById('hidLng').value=" & oMarker.ID & ".getPoint().lng() }"))

    End Sub

And here is the ‘Save’ button click event:

    Protected Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Response.Write("New Latitude =" & hidLat.Value & ", New Longitude = " & Me.hidLng.Value)
    End Sub

Ever wanted to add a Google Map to your site but only had 15 minutes to spare? Now you can add a map and still have time to brag to your mates and bask in the worship that (inevitably) comes afterward.

Basically, the guys over at subgurim.net have already done all the hard work in writing the .Net wrapper for Google Maps. Problem is, the examples on their site are mostly in spanish & its a bit difficult to find out exactly what is needed to get everything working.

But all this is cutting into your bragging time - so lets get started!

1. Get a Google Maps API key from here:
http://www.google.com/apis/maps/

2. Download the SubGurim wrapper dll from here:
http://en.googlemaps.subgurim.net/descargar.aspx

3. Unzip it, and put it in your \bin directory

4. Add it to your toolbox by
Tools -> Choose Toolbox Items -> Browse -> Select the .dll file -> OK
GMap will now be in the ‘Standard’ area of your Toolbox.

5. Add a new webpage.

6. Drag the GMap from the toolbox onto the page. A new instance of the GMap will appear on the page, with the name ‘GMap1′

7. Add the following lines to your web.config file:

  <appSettings>
    <add key="googlemaps.subgurim.net" value="YourGoogleMapsAPIKeyHere" />
  </appSettings>

8. Add the following code to your Page.Load sub

        Dim sStreetAddress As String
        Dim sMapKey As String = ConfigurationManager.AppSettings("googlemaps.subgurim.net")
        Dim GeoCode As Subgurim.Controles.GeoCode

        sStreetAddress = "100 Russell St. Melbourne. VIC. 3000. Australia"
        GeoCode = GMap1.geoCodeRequest(sStreetAddress, sMapKey)
        Dim gLatLng As New Subgurim.Controles.GLatLng(GeoCode.Placemark.coordinates.lat, GeoCode.Placemark.coordinates.lng)

        GMap1.setCenter(gLatLng, 16, Subgurim.Controles.GMapType.GTypes.Normal)
        Dim oMarker As New Subgurim.Controles.GMarker(gLatLng)
        GMap1.addGMarker(oMarker)

Press F5, and start basking in the glory!

Update: I’ve now posted the code to add draggable markers and events to your Google Maps