Hi,
I'm wondering if anyone can help me?
I have a simple form in VB that contains one button and one MapPoint control. I'm only experimenting at this stage but would like the button to show/refresh data which is held on a SQL server using a UDL file.

The form loads but error's when I click on the button.
Here's all of the code currently attached to the form:


Public Class MainForm


Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

AxMappointControl1.OpenMap("MyBlankMap.ptm")

'Display the toolbars

AxMappointControl1.Toolbars.Item("location and scale").Visible = True

AxMappointControl1.Toolbars.Item("navigation").Vis ible = True

AxMappointControl1.Toolbars.Item("standard").Visib le = True

End Sub



Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim objApp As MapPoint.Application

Dim objDS As MapPoint.DataSet

Dim objMap As MapPoint.Map

objApp.Visible = True ' The debugger stops on this line

objApp.UserControl = True

Dim arrFields(0 To 11, 0 To 1)

arrFields(0, 0) = "jobid" : arrFields(0, 1) = MapPoint.GeoFieldType.geoFieldData

arrFields(1, 0) = "jobtype" : arrFields(1, 1) = MapPoint.GeoFieldType.geoFieldData

arrFields(2, 0) = "assignedto" : arrFields(2, 1) = MapPoint.GeoFieldType.geoFieldData

arrFields(3, 0) = "actiondate" : arrFields(3, 1) = MapPoint.GeoFieldType.geoFieldData

arrFields(4, 0) = "externaluser" : arrFields(4, 1) = MapPoint.GeoFieldType.geoFieldData

arrFields(5, 0) = "complete" : arrFields(5, 1) = MapPoint.GeoFieldType.geoFieldData

arrFields(6, 0) = "name" : arrFields(6, 1) = MapPoint.GeoFieldType.geoFieldData

arrFields(7, 0) = "customerpriority" : arrFields(7, 1) = MapPoint.GeoFieldType.geoFieldData

arrFields(8, 0) = "latitude" : arrFields(8, 1) = MapPoint.GeoFieldType.geoFieldLatitude

arrFields(9, 0) = "logitude" : arrFields(9, 1) = MapPoint.GeoFieldType.geoFieldLongitude

arrFields(10, 0) = "doorder" : arrFields(10, 1) = MapPoint.GeoFieldType.geoFieldData

With objMap.DataSets

objDS = .LinkData("test.udl!Deliveries", arrFields, MapPoint.GeoCountry.geoCountryUnitedKingdom, MapPoint.GeoDelimiter.geoDelimiterDefault)

End With
objDS.ZoomTo()

End Sub
End Class


When I click the button I see the following errors:
Variable 'objApp' is used before it has been assigned a value. A null reference exception could result at runtime.
Variable 'objMap' is used before it has been assigned a value. A null reference exception could result at runtime.


Any pointers (or tidied code) would be very much appreiciated.
I have only ever done minimal coding in the past.

Thanks
Simon

Hi Simon,

This is because of the following. If you do:

Code:

Dim objApp As MapPoint.Application

Then you tell the compiler that this variable objApp is of type MapPoint.Application. But the variable contains nothing at all. So the error is correct, it is not assigned a value. You have to do something similar as:

Code:

objApp = CreateObject("MapPoint.Application.EU.13")

But there is something else. You use the activeX control on your form. I dont knowin VB, but in C# it is impossible to use the activeX control in parallel with mappoint.application. But normally this is also not needed.

All the things you wants to do with Mappoint.Application you can do with the activeX control. Check therefore:

Code:

AxMappointControl1.ActiveMap....

With the .... I mean what follows there.