Excel Interop - Efficiency and performance

Question

I was wondering what I could do to improve the performance of Excel automation, as it can be quite slow if you have a lot going on in the worksheet...

Here's a few I found myself:

• ExcelApp.ScreenUpdating = false -- turn off the redrawing of the screen

• ExcelApp.Calculation = Excel.XlCalculation.xlCalculationManual -- turning off the calculation engine so Excel doesn't automatically recalculate when a cell value changes (turn it back on after you're done)

• Reduce calls to Worksheet.Cells.Item(row, col) and Worksheet.Range -- I had to poll hundreds of cells to find the cell I needed. Implementing some caching of cell locations, reduced the execution time from ~40 to ~5 seconds.

What kind of interop calls take a heavy toll on performance and should be avoided? What else can you do to avoid unnecessary processing being done?

Answer 1

Performance also depends a lot on how you automate Excel. VBA is faster than COM automation is faster than .NET automation. And typically early (compile time) binding is faster than late binding, too.

If you have serious performance problems you could think of moving the critical parts of the code to a VBA module and call that code from your COM/.NET automation code.

If you use .NET you should also use the optimized primary interop assemblies available from Microsoft and not use custom-built interop assemblies.

Answer 2

Use excels builtin functionality whenever possible, for example: Instead of searching a whole column for a given string, use the find command available in the GUI by Ctrl-F:

Set Found = Cells.Find(What:=SearchString, LookIn:=xlValues, _
    SearchOrder:=xlByRows, SearchDirection:=xlNext, _
    MatchCase:=False, SearchFormat:=False)

If Not Found Is Nothing Then
    Found.Activate
    (...)
EndIf

If you want to sort some lists, use the excel sort command, don't do it manually in VBA:

Selection.Sort Key1:=Range("A1"), Order1:=xlAscending, Header:=xlGuess, _
    OrderCustom:=1, MatchCase:=False, Orientation:=xlTopToBottom, _
    DataOption1:=xlSortNormal

Answer 3

If you're polling values of many cells you can get all the cell values in a range stored in a variant array in one fell swoop:

Dim CellVals() as Variant
CellVals = Range("A1:B1000").Value

There is a tradeoff here, in terms of the size of the range you're getting values for. I'd guess if you need a thousand or more cell values this is probably faster than just looping through different cells and polling the values.

Answer 4

When using C# or VB.Net to either get or set a range, figure out what the total size of the range is, and then get one large 2 dimensional object array...

//get values
object[,] objectArray = shtName.get_Range("A1:Z100").Value2;
iFace = Convert.ToInt32(objectArray[1,1]);

//set values
object[,] objectArray = new object[3,1] {{"A"}{"B"}{"C"}};
rngName.Value2 = objectArray;

Note that its important you know what datatype Excel is storing (text or numbers) as it won't automatically do this for you when you are converting the type back from the object array. Add tests if necessary to validate the data if you can't be sure beforehand of the type of data.