[GIS] ArcMap Form/Button VB.NET MxDocument hook

arcgis-9.3arcobjectsvb.net

—UPDATE— see below

I have a scaling raster tool that I'm attempting to migrate from ArcGIS 9.3.1 VBA to VB.NET (Visual Studio 2010). I have a BaseTool that is used to put two graphic points defining the left and right extent of the image that I want to scale. After the second point is added to the view a form opens to input the scaling parameters. My issues is when I go to click the scale command button (within the form) I get the "Null Reference Exception was unhandled by user code, Object reference not set to an instance of an object", error. The error occurs on this line:

pMap = m_pMxDoc.FocusMap

I have my ESRI references imported into the project for both pMap and m_pMxDoc. It seems like the form is not hooked to the ArcMap document? I tried to hook the form on load via the code below, but I get the same error.

Private Sub frmScaling_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
            Dim hook As Object = Nothing
            m_application = hook
            m_pMxDoc = m_application.Document
End Sub

Any suggestions of what I'm missing would be greatly appreciated.

Thanks

—UPDATE—

I created the docable window class and memebers. The On Create sub now is:

Public Sub OnCreate(ByVal hook As Object) Implements ESRI.ArcGIS.Framework.IDockableWindowDef.OnCreate

        m_application = hook
        m_pMxDoc = m_application.Document

End Sub

Now when I click the command button within my form to scale the image I get a LoaderLock error (Attempting managed execution inside OS Loader lock. Do not attempt to run managed code inside a DllMain or image initialization function since doing so can cause the application to hang). The error is still on this line:

pMap = m_pMxDoc.FocusMap

Is this error present because my form is open while the scaling action is trying to take place? So, the hook is now on the member "On Create", do I also need to hook within the button click on the form?

Are there any other good VB.NET form/code examples within ArcMap that contain some sort of button that interacts with the ArcMap view? I have only found this one,

Best Answer

As long as you have 

Dim hook As Object = Nothing

You will get a null refrence exception when you access it.

You may want to read up on how to create commands and tools in ArcMap. You will certainly want to handle the OnCreate event - since that is where you get the "hook" from.

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