Late bind an IHTML element

I'm trying to create a late bound VBA project to search the web. At one point I have the following code (early bound):

Dim currPage as HTMLDocument: Set currPage = objIE.document 'where objIE is set with Set objIE = CreateObject("InternetExplorer.application")
'(late bound as it is dim'd as Object)
    Dim myDiv As HTMLDivElement: Set myDiv = currPage.getElementById("fbar")
    Dim elemRect As IHTMLRect: Set elemRect = myDiv.getBoundingClientRect
    'Scroll until bottom of page is in view
    Do Until elemRect.bottom > 0
        currPage.parentWindow.scrollBy 0, 10000
        Set elemRect = myDiv.getBoundingClientRect
    Loop

This code becomes this when late bound: (or so I thought)

Dim currPage as Object: Set currPage = objIE.document
    Dim myDiv As Object: Set myDiv = currPage.getElementById("fbar")
    Dim elemRect As Object: Set elemRect = myDiv.getBoundingClientRect
    'Scroll until bottom of page is in view
    Do Until elemRect.bottom > 0
        currPage.parentWindow.scrollBy 0, 10000
        Set elemRect = myDiv.getBoundingClientRect
    Loop

The problem, I'm guessing, lies with the I infront of IHTMLRect, which MSDN tells me denotes an element on a web page which doesn't have an actual object associated with it - consequently assigning it to an unspecified Object just makes no sense in the code. (That's a complete guess)

Anyway, the early bound code works fine, the late bound code quits execution at elemRect.bottom

Why is this and how can I fix it?

Solution

Objects in VBA can implement multiple interfaces and the methods/properties you can call depend on the interface that you are using to access the object. A simple example:

' This means access the object via the IUnknown interface
' IUnknown is the interface from which all other COM
' interfaces inherit
Dim x As IUnknown
Set x = ThisWorkbook.Worksheets(1)

' Commented out as this won't compile because the
' Name property isn't defined in IUnknown
' MsgBox x.Name

' This means access the object through the default
' interface associated with the Worksheet object type
Dim w As Worksheet
Set w = x

' Now we can get to the name (same object, different interface)
MsgBox w.Name

In the case of MSHTML, I would guess that methods like getElementById are returning an interface like one of the versions of IHTMLElement. This means that methods/properties defined in an interface like IHTMLDivElement can't be accessed.

IUnknown has a method called QueryInterface which is used to get to the different interfaces which the object implements. This cannot be called directly in VBA, however, as the VBA way of doing this is by using Dim with the appropriate interface and then using Set. This will only compile if the necessary references have been set which in turn defeats the purpose of late binding.

There is a workaround using CallByName. To go back to the worksheet example, this works:

Dim x As IUnknown
Set x = ThisWorkbook.Worksheets(1)

' Commented out as this won't compile because the
' Name property isn't defined in IUnknown
' MsgBox x.Name

' Can get to the property via CallByName
MsgBox CallByName(x, "Name", VbGet)

For the MSHTML issue, this works (note that the call type is changed to VbMethod):

Dim elemRect As Object: Set elemRect = CallByName(myDiv, "getBoundingClientRect", 
    VbMethod)
stTimer = Timer
'Scroll until bottom of page is in view
Do Until elemRect.bottom > 0 Or tElapsed > timeout 'timeout after n seconds
    currPage.parentWindow.scrollBy 0, 10000
    Set elemRect = CallByName(myDiv, "getBoundingClientRect", VbMethod)
    tElapsed = Timer - stTimer
Loop

I know very little about COM objects so there may well be other issues which I have failed to consider

Full code (adapted from your answer to another question). Running the function repeatedly in quick succession produces errors due to IE taking time to shutdown (see this question for a similar issue). Re-use the same IE object if you need to run multiple queries in succession:

Option Explicit

Public Function GOOGLE_COUNT(searchTerm As String, xRes As Long, yRes As Long, Optional timeout As Long = 10) As Long

    Dim url As String
    Dim objIE As Object
    Dim currPage As Object
    Dim stTimer As Double, tElapsed As Single
    Dim valueResult As Object

    'create URL to page with these image criteria
    url = "https://www.google.com/search?q=" & searchTerm & _
                        "&tbm=isch&source=lnt&tbs=isz:ex,iszw:" & xRes & ",iszh:" & yRes

    'initiating a new instance of Internet Explorer and asigning it to objIE
    Set objIE = CreateObject("InternetExplorer.Application")

    'Google images search
    objIE.navigate url
    Do While objIE.Busy = True Or objIE.readyState <> 4: DoEvents: Loop
    Set currPage = objIE.document
    Dim myDiv As Object: Set myDiv = currPage.getElementById("fbar")
    Dim elemRect As Object: Set elemRect = CallByName(myDiv, "getBoundingClientRect", VbMethod)
    stTimer = Timer
    'Scroll until bottom of page is in view
    Do Until elemRect.bottom > 0 Or tElapsed > timeout 'timeout after n seconds
        currPage.parentWindow.scrollBy 0, 10000
        Set elemRect = CallByName(myDiv, "getBoundingClientRect", VbMethod)
        tElapsed = Timer - stTimer
    Loop
    myDiv.ScrollIntoView
    'Count the images
    Set valueResult = currPage.getElementById("rg_s").getElementsByTagName("IMG")
    GOOGLE_COUNT = valueResult.Length
    objIE.Quit

End Function

Sub foo()

MsgBox GOOGLE_COUNT("St. Mary", 1366, 768)

End Sub