Delphi OLE - How to avoid errors like "The requested member of the collection does not exist"?

I'm automating Word with Delphi, but some times I got an error message:

The requested member of the collection does not exist

It seems that the Item memb开发者_StackOverflow中文版er of the Styles collection class does not always exist and some times causes the above mentioned error. My workaround is to catch the exception and skip it, but is there anyway to detect it instead of using the try...except block? The problem with the try...except block is that when debugging the raised exception is annoying...

My code example:

var
  aWordDoc: _WordDocument
  i: Integer;
  ovI: OleVariant;
  wordStyle: Style;
begin
  for i := 1 to aWordDoc.Styles.Count do
  begin
    ovI := i;
    try
      wordStyle := aWordDoc.Styles.Item(ovI);
    except
      Continue;//skip if any error occurred.
    end;

    //do something with wordStyle
  end;
end

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If the compiler accepts it, but it sometimes cannot happen to exist, it is probably IDispatch based latebinding. IDispatch objects can be queried. Maybe carefully working yourself up the tree querying every object for the next would work.

You would then roughly be doing what the compiler does, except that that one throws an exception if somethines doesn't exist. (and if the exception comes in from COM, maybe a slightly different code path can test more).

Sorry to have no readily made code.

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I get that message when a bookmark that I'm trying to fill from Word doesn't exist so i have a process that checks first, but I'm not sure the same method would work for you.

procedure MergeData(strBookMark, strData : string);
begin
  if WinWord.ActiveDocument.Bookmarks.Exists(strBookMark) = True then
    WinWord.ActiveDocument.FormFields.Item(strBookMark).Result := strData;
end;

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It has nothing to do with the Item function not being there. The Item function does exists, but the index you give seems to be wrong.

See this msdn article.

An invalid index seems really weird, because you are performing a for loop from 1 to Styles.Count. So if there is no Style, you should not enter the loop.

The only plausible explanation I can think of is that while you are in your loop, the Styles.Count changes and you are getting out of bounds. Are you deleting styles in your loop perhaps? Try a loop going from Styles.Count downto 1 or try a While loop, evaluating Styles.Count at every iteration.

Other things I can think of, but are very unlikely:

• While assigning I to ovI, it gets converted to an OleString, so Word searches for a style named "I", instead of a Style at I
• While assigning I to ovI, something in the conversion goes wrong and it gets in the range of $FFFFFFA5 - $FFFFFFFF, which are constants for Builtin styles.

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try checking if it is null or not with a IF statement