Macro for inserting a mini table between heading styles

I am using the following macro to insert a mini table of contents between two identical heading styles (e.g. Heading 1). It works fine on small documents, but is very slow on large documents.

`Sub MiniTOCFields(HeadingNumber As Long, TOCLevel As Long)
' Add mini TOC fields after all occurrences of a Heading style.
' HeadingNumber defines which heading style to add miniTOCs to (e.g. Heading 1).
' TOCLevel defines to what heading level the TOC shows (e.g. down to Heading 3).

Dim bookmarkNumber As Long
Dim bookmarkRange As Range
Dim insertRange As Range
Dim currentParagraph As Paragraph
Dim paragraphNumber As Long
Dim currentTOC As TableOfContents

bookmarkNumber = 0
paragraphNumber = 0

Set bookmarkRange = ActiveDocument.Paragraphs(1).Range

' Cycle through each paragraph
For Each currentParagraph In ActiveDocument.Paragraphs
paragraphNumber = paragraphNumber + 1

' Check for occurrences of Heading X
If currentParagraph.Style = "Heading " & HeadingNumber Then

' If this is not the first occurrence, create a bookmark between this and the last one
If bookmarkNumber > 0 Then
' Move the end of the bookmark to the end of the next paragraph
bookmarkRange.End = ActiveDocument.Paragraphs(paragraphNumber - 1).Range.End
' Create bookmark
ActiveDocument.Bookmarks.Add _
Name:="TOCHeading" & HeadingNumber & "_" & bookmarkNumber, _
Range:=bookmarkRange
End If

' Move the start of the bookmark to the beginning of the next paragraph
bookmarkRange.Start = ActiveDocument.Paragraphs(paragraphNumber + 1).Range.Start

' Add the TOC field
Set insertRange = currentParagraph.Range
insertRange.Collapse direction:=wdCollapseEnd
' Add the new TOC field
ActiveDocument.Fields.Add _
Range:=insertRange, _
Type:=wdFieldEmpty, _
Text:=" TOC \h \o """ & HeadingNumber & "-" & TOCLev

Optimization:

You've done a good job of making sure you're not processing more than you have to, but there are a couple of things you can do here to improve performance. Instead of looping through all of the MiniTOCs you've just inserted, updating each one individually. Just update all of the fields in the entire document at once.

Replace This:

' Update all TOC fields in document
For Each currentTOC In ActiveDocument.TablesOfContents
     currentTOC.Range.Select
     currentTOC.Update
Next currentTOC

With This:

ActiveDocument.Fields.Update

It also turns out that there's no reason to to check every paragraph's style. We can find them all. Below is the uber simplified logic that you would need to implement. Also note that subs/functions should have a verb-noun type name. I changed it in my example.

Private Sub test()
    InsertMiniTOCFields wdStyleHeading1, 3
End Sub

Public Sub InsertMiniTOCFields(headingStyle As WdBuiltinStyle, TOClevel As Long)
    Dim bookmarkRange As Range
    Dim bookmarkNumber As Long
    Dim currentRange As Range
    Dim insertRange As Range
    Dim doc As Document

    Set doc = ActiveDocument
    Set currentRange = doc.Range 'start with the whole doc as the current range

    With currentRange.Find
        .Forward = True         'move forward only
        .Style = headingStyle   'the style given as an argument
        .Execute                'update currentRange to next found instance

        Do While .Found

            ' code to insert bookmarks

            ' Add the TOC field
            Set insertRange = currentRange 'I changed this assignment from currentParagraph to currentRange
            insertRange.Collapse direction:=wdCollapseEnd
            ' Add the new TOC field
            doc.Fields.Add _
                Range:=insertRange, _
                Type:=wdFieldEmpty, _
                Text:=" TOC \h \o """ & HeadingNumber & "-" & TOClevel & """ \b TOCHeading" & HeadingNumber & "_" & (bookmarkNumber + 1)
                bookmarkNumber = bookmarkNumber + 1

            ' update currentRange to next found instance
            .Execute
        Loop
    End With

    'update all newly inserted MiniTOCs
    doc.Fields.Update

End Sub

You can also turn screen updating off to pick up some more performance. You will need to introduce some error handling into your code if you decide to do that though. You'll want to make sure that screen updating is always turned back on when your sub exits; even if it errors. Truthfully, I imagine that this routine should really have an error handler anyway. Here is a pretty good error handling pattern to follow.

Other Notes:

-
You really shouldn't access the document with ActiveDocument each time. It's much better to store the reference in a variable. This way, you know for a fact that the document you started working on is the one you'll continue to work on.

Dim doc as Document
Set doc = ActiveDocument

-
Watch your line indentation. Ends should be at the same indentation
level as the If they belong to.

-
Instead of declaring HeadingNumber as a long in your sub
declaration, you should consider using WdBuiltInStyle.

So instead of this:

Sub MiniTOCFields(HeadingNumber As Long, TOCLevel As Long)  
    '......
    ' Check for occurrences of Heading X
     If currentParagraph.Style = "Heading " & HeadingNumber Then

You would have this:

Sub MiniTOCFields(headingStyle As WdBuiltInStyle, TOCLevel As Long)  
    '......
    ' Check for occurrences of Heading X
     If currentParagraph.Style = headingStyle Then

You write pretty clean code. I like your variable names. Very concise and easily understandable. You use line continuations judiciously, but it can be a slippery slope. Be careful with that.

StackExchange Code Review Q#54028, answer score: 8