DPLOTLIB.DLL with VB 2008

[Mao]

David:

I successfully developed an application with VB 2005 that called DPLOTLIB.DLL using the example included with the software:

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Public Sub DPlot_FindDPLOTLIB() 
    ' Find DPLOTLIB.DLL. 
    Dim key As Microsoft.Win32.RegistryKey 
    Dim path As String 
    Dim hLib As IntPtr 

    hLib = LoadLibrary("dplotlib.dll") 
    If hLib <> 0 Then 
        ' If LoadLibrary finds the DLL, then so will VB.NET, so there's 
        ' no need to look in the registry or change the current 
        ' directory 
        FreeLibrary(hLib) 
        Exit Sub 
    End If 

    key = Microsoft.Win32.Registry.CurrentUser.OpenSubKey("Software\\DPLOT\\DPLOTLIB\\Folder") 
    path = key.GetValue("").ToString() 
    key.Close() 
    If Len(path) > 0 Then 
        System.Environment.CurrentDirectory = path 
    End If 
End Sub

Recently I migrated to VB 2008 but the code does not run anymore; it stops in the line:

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path = key.GetValue("").ToString()

and reports the following message:

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System.NullReferenceException was unhandled
  Message="Object reference not set to an instance of an object."

and recommends to:

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Use the "new" keyword to create an object instance.

Has somebody reported the same problem with VB 2008 ?

Thanks.

Mao

[DPlotAdmin]

I'm not sure but it seems to me the error message means that the key doesn't exist, and you need to check against it being "Is Nothing" before using GetValue. But I may be wrong.

You'll likely have much better luck posting this question on any of the numerous VB boards, since it really has nothing to do with DPlot.

[BillGrissom]

Mao,

I converted a VB6 program that calls Dplot to VB2008 over 1 year ago. I didn't changed anything in sub Dplot_FindDPLOTLIB and I don't see that the auto-converter changed anything.

Anyway, I copied your lines next to mine and see no difference.

I agree that most likely your dll became unregistered. Try typing the following in a CMD window:

regsvr32 /u dplotlib.dll
regsvr32 dplotlib.dll

The first unregisters the dll (if it finds it) and 2nd registers it.
Don't ask me how it knows where to put it in the Registry, that must be embedded within the dll. This has worked for me several times, even when basic Windows dll's get unregistered (maybe a mistaken script that my I.S. department ran).

[DPlotAdmin]

I'm probably in over my head here, but to the best of my knowledge regsvr32 is only useful for COM objects, and dplotlib.dll does not use COM. If I go to the folder containing dplotlib.dll with a command prompt and type
regsvr32 dplotlib.dll
I get an error message about DLLRegisterServer and whether the DLL uses OCX (it doesn't).

Short version: whatever problem BillGrissom is having is almost certainly not due to using/not using regsvr32.

[BillGrissom]

Old post. I just ran across this.

I didn't mean to imply that I ever used the regsvr32 commands on any Dplot files, and indeed never had the issues the OP is having. I have used that command to fix another app (Pacific Instruments), per their suggestions and works there. Perhaps they use COM. I just threw it out as a simple thing to try. Sounds like it isn't relevant to Dplot.

[BillGrissom]

Old post. I just ran across this.

I didn't mean to imply that I ever used the regsvr32 commands on any Dplot files, and indeed never had the issues the OP is having. I have used that command to fix another app (Pacific Instruments), per their suggestions and works there. Perhaps they use COM. I just threw it out as a simple thing to try. Sounds like it isn't relevant to Dplot.