While writing iLogic rules I find my self often in the situation that I need to find a object in a list. Often I can use a standard Inventor api functions. But in some cases they do not work or the function just does not exists. For example I have the following situation. While generating drawings with our product configurator. An iLogic rule adds dimensions to an idw with many sheets. Ofcourse in that ILogic rule I need to select the correct sheet (in a list of sheets).

I have 2 options. Use the iLogic api and call the function:

Dim sheets As IManagedSheets = ThisDrawing.Sheets
Dim sheet As IManagedSheet = sheets.ItemByName("MySheetName:15")

 (Notic the types start with IManaged… that is a sign we use the iLogic api)

The problem here is the sheet number (15) at the end of the sheet name. That number is added by Inventor and it will change if an other sheet is removed. Maybe needless to say but our configurator removes sheets…. So that does not work for me. The other option is to use the Inventor api. I can get a sheet like this:

Dim sheets As Sheets = ThisDrawing.Document.Sheets
Dim sheet As Sheet = sheets.Item(15)

 (notice the “Document” property that gives us access to the Inventor api.) 

As you probably can guess this number will also change when a sheet is removed. Therefor this also doesn’t work for me. The most obvious solution would be to loop over all sheets and check each name. something like this:

Dim sheets As Sheets = ThisDrawing.Document.Sheets
Dim sheet As Sheet = Nothing
For Each currentSheetInLoop As sheet In sheets
    If (currentSheetInLoop.Name.Contains("MySheetName")) Then
        sheet = currentSheetInLoop
        Exit For
    End If
Next

 But there is a more elegant solution that does exactly the same thing:

Dim sheet As Sheet = ThisDrawing.Document.Sheets.
	Cast(Of Sheet).
	Where(Function(s) s.Name.Contains("MySheetName")).
	FirstOrDefault()

 I think this is more readable then the whole loop also it’s more flexible. In this 4 lines I have chained a lot of functions/properties one after the other.  Usaly i would not advice to do this because its dificult to debug, but in this case there isn't much that can go wrong. (I could have done this in 1 line but that would have been less readable.) Lets have a look what is going on here and breaking it down in separate lines. 

'Get the list of sheets Inventor api style 
Dim sheets As Sheets = ThisDrawing.Document.Sheets

'Cast the list to the type IEnumerable list. 
'IEnumerable list is a standard vb.Net type. With the some greate (extension) functions like "Where" 
Dim allSheets As IEnumerable(Of Sheet) = sheets.Cast(Of Sheet)

'Here we use the function "Where" to find all sheets that 
'comply with the following statement: Sheet._DisplayName.Contains("MySheetName")
'think of this as the statement in an "If" function.
Dim sheetsSubSet As IEnumerable(Of Sheet) = allSheets.Where(Function(s) (s.Name.Contains("MySheetName")))
'Notice that this is also an IEnumerable list. 
'The "Where" function is like a filter on a list that returns a list. 
'If you want you could use multiple filters here ;-)

'If your filter is correct you will end up with a list of 1 item.
'You will get the first item of the list like this. 
'That has to be the item/sheet that you where looking for
Dim sheet As Sheet = sheetsSubSet.FirstOrDefault()

 If you want to test this function, I would suggest the following code:

Dim sheet As Sheet = ThisDrawing.Document.Sheets.
	Cast(Of Sheet).
	Where(Function(s) s.Name.Contains("MySheetName")).
	FirstOrDefault()

If (sheet Is Nothing) Then
    MsgBox("Sheet not found")
Else 
    MsgBox(sheet.Name)
End If