OLEVariants problem

[daveinhull]

Hi,

I have a problem with an OLEVariant (connects to Excel).
When I cloase a particualr form I want to make sure that the Excel object is also closed, so I have used

Code: Pascal  [Select][+][-]

1. If ExcelServer <> Unassigned then
2. begin
3.   ExcelServer.ActiveWorkbook.Close (False);
4.   if ExcelServer.Workbooks.Count = 0 then
5.     ExcelServer.Quit;
6.     ExcelServer := Unassigned;
7.   end
8. ....

Which is ok if the ExcelServer was never assigned during the program execution, i.e. the user didn't want to do anything with Excel.

However, it fails with an "Invalid Variant Operation Displatch = Empty" message if I actually do setup a link to Excel.
If I change the code

Code: Pascal  [Select][+][-]

1. if ExcelServer <> Null then

it also fails.

Anybody got any thoughts in this?

Dave

[rvk]

Maybe

Code: Pascal  [Select][+][-]

1. if not VarIsEmpty(ExcelServer) then

[Thaddy]

I expected VarNull or VarEmpty

[rvk]

VarIsEmpty checks for VarEmpty. It's just a wrapper for the check. You shouldn't check for VarEmpty directory.

VarIsEmpty returns true if the given variant contains the value Unassigned.

So to make sure you could also do

Code: Pascal  [Select][+][-]

1. if not VarIsNullthen(ExcelServer) and not VarIsEmpty(ExcelServer) then //...

O yeah, to make it more confusing there is also VarIsClear()

Also note the function:

Code: Pascal  [Select][+][-]

1. function VarIsEmpty(const V: Variant): Boolean;
2. begin
3.   Result:=TVarData(V).vType=varEmpty;
4. end;

So that's something different from

Code: Pascal  [Select][+][-]

1. if Variant <> varEmpty then ... // <-- incorrect

So

• Check for unassigned with VarIsEmpty.
• Check for an undefined value with VarIsClear.
• Check for a null value with VarIsNull.

[daveinhull]

Thanks guys,

This worked

Maybe

Code: Pascal  [Select][+][-]

1. if not VarIsEmpty(ExcelServer) then

And thanks for the other info as well, all useful learning 

Dave