VB.NET Releasing Excel file after reading so it can be overwritten - vb.net

Question

I am having the same issue that many before me have had, and I have found several threads on the issue but my application of their fixes have not yielded any change.
I am reading an excel file and populating a DataGridView with it. Very simply the user can modify it and then save it. The problem, like the other threads, is that the program has such a tight grip on the file I can't overwrite it.
Among the many fixes offered, Garbage Collection was the most frequently mentioned, but my results are unchanged. I have tried disposing of the OLEDB connection, commands, adapters and datasets also without success.
I've been running through several different examples and tutorials to write this program and so if these fixes are required, I've obviously implemented them in the wrong spot.
Here is the reading block which happens on the form load (I've removed all my attempts to fix it to unclutter the code):
Private Sub Inventory_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Using MyConnection = New System.Data.OleDb.OleDbConnection("provider=Microsoft.Jet.OLEDB.4.0;Data Source='c:\AllTrade\Inventory.xlsx';Extended Properties=Excel 8.0;")
Using MyCommand = New System.Data.OleDb.OleDbDataAdapter("select * from [InventorySheet$]", MyConnection)
DtSet = New System.Data.DataSet
MyCommand.Fill(DtSet)
InventoryGridView.DataSource = DtSet.Tables(0)
MyConnection.Close()
End Using
End Using
End Sub
Here is the saving block (This is the code that generates the "File in Use" error):
Private Sub UpdateInventory_Click(sender As Object, e As EventArgs) Handles UpdateInventory.Click
Dim ExcelApp As New Excel.Application()
ExcelApp.Application.Workbooks.Add(Type.Missing)
For i As Integer = 0 To InventoryGridView.Rows.Count - 1
Dim row As DataGridViewRow = InventoryGridView.Rows(i)
For j As Integer = 0 To row.Cells.Count - 1
ExcelApp.Cells(i + 1, j + 1) = row.Cells(j).Value
Next
Next
ExcelApp.ActiveWorkbook.SaveAs("C:\Alltrade\Inventory.xlsx")
ExcelApp.ActiveWorkbook.Saved = True
ExcelApp.Quit()
End Sub
What's the trick to let go of the file? If the GC.Collect() and GC.WaitForPendingFinalizers() are required, where would they go?
I appreciate any help and apologize since I haven't been able to successfully implement the other answers from similar threads.

Answer 1

You need to marshal to release the COM object: ExcelApp...
Private Sub ReleaseObject(ByVal obj As Object)
Try
Dim intRel As Integer = 0
Do
intRel = System.Runtime.InteropServices.Marshal.ReleaseComObject(obj)
Loop While intRel > 0
Catch ex As Exception
MsgBox("Error releasing object" & ex.ToString)
obj = Nothing
Finally
GC.Collect()
End Try
End Sub
You can call this method like this at the end of your sub.
ReleaseObject(ExcelApp)
You can get more here Excel application not quitting after calling quit
EDIT
I also noticed your connection string is wrong for the newer .xlxs file extention...
Normal ConnectionString : (work for xls files)
"Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties=\"Excel 8.0;HDR=YES;\""
Office 2007 ConnectionString : (work for xlsx files)
"Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties=\"Excel 12.0;HDR=YES;\""

Answer 2

After much research and frustration, I found a solution.
The connection string of my OleDB connection needs the tidbit added: OLE DB Services = -4 which disables connection pooling. As it happens, the connection is not disposed of (which was the initial hypothesis) when the connection is closed, but instead dumps the connection back into the pool.
Another forum had suggested OLE DB Services = -2 which was supposed to do the same thing, but had no effect in my instance. It's possible it varies between versions but I haven't researched this to conclude that for certain (or someone typoed in one of the forums)
No further code was required in my program to dump the OleDB connection's hold on the file. MyConnection = Nothing and the line that drains the pool followed by a GC.Collect were also recommended but did not resolve my symptoms.
Thanks everyone for the input