Reading excel files in vb.net leaves excel process hanging - vb.net

Question

The following code works fine but seems to leave instances of excel.exe running in the background. How do I go about closing out this sub properly?
Private Sub ReadExcel(ByVal childform As Fone_Builder_Delux.frmData, ByVal FileName As String)
' In progress
childform.sampleloaded = False
Dim xlApp As Excel.Application
Dim xlWorkBook As Excel.Workbook
Dim xlWorkSheet As Excel.Worksheet
xlApp = New Excel.ApplicationClass
xlWorkBook = xlApp.Workbooks.Open(FileName)
xlWorkSheet = xlWorkBook.Worksheets(1)
Dim columnrange = xlWorkSheet.Columns
Dim therange = xlWorkSheet.UsedRange
childform.datagridHeaders.Columns.Add("", "") ' Super imporant to add a blank column, could improve this
For cCnt = 1 To therange.Columns.Count
Dim Obj = CType(therange.Cells(1, cCnt), Excel.Range)
childform.datagridSample.Columns.Add(Obj.Value, Obj.Value)
childform.datagridHeaders.Columns.Add(Obj.Value, Obj.Value)
Next
For rCnt = 2 To therange.Rows.Count
Dim rowArray(therange.Columns.Count) As String
For cCnt = 1 To therange.Columns.Count
Dim Obj = CType(therange.Cells(rCnt, cCnt), Excel.Range)
Dim celltext As String
celltext = Obj.Value.ToString
rowArray((cCnt - 1)) = celltext
'MsgBox(Obj.Value)
Next
childform.datagridSample.Rows.Add(rowArray)
Next
AdjustHeaders(childform)
childform.sampleloaded = True
End Sub

Answer 1

Short answer: close each item appropriately, then call FinalReleaseComObject on them.
GC.Collect()
GC.WaitForPendingFinalizers()
If xlWorkSheet Is Nothing Then Marshal.FinalReleaseComObject(xlWorkSheet)
If xlWorkBook Is Nothing Then
xlWorkBook.Close(false, false)
Marshal.FinalReleaseComObject(xlWorkBook)
End If
xlApp.Quit()
Marshal.FinalReleaseComObject(xlApp)
Long answer: read this answer to another question (the entire post is helpful too).

Answer 2

I ran into this problem and what I found worked was making sure I called the Close() method on all Workbook and Workbooks objects, as well as the Quit() method on the Excel Application object. I also call System.Runtime.InteropServices.Marshal.ReleaseComObject on every Excel object was instantiated. I do all this in reverse order of age, so the newest object gets cleaned up first and the oldest, which is the Application object, gets taken care of last. I don't know if the order really matters, but it seems like it might.
I've seen examples where GC.Collect() was called at the very end, but I've never had to do that to get the excel.exe process to end.