Excel Range object throws error 0x800A03EC because of a string longer than 255 characters - matlab

Question

Using an ActiveX server from MATLAB, I am trying to highlight many cells in an Excel sheet at once. These are not in specific columns or rows so I use Range('A1,B2,...') to access them. However the string accepted by the Range object has to be less than 255 characters or an error:
Error: Object returned error code: 0x800A03EC
is thrown. The following code reproduces this error with an empty Excel file.
hActX = actxserver('Excel.Application');
hWB = hActX.Workbooks.Open('C:\Book1.xlsx');
hSheet = hWB.Worksheets.Item('Sheet1');
col = repmat('A', 100, 1);
row = num2str((1:100)'); %'
cellInd = strcat(col, strtrim(cellstr(row)));
str1 = strjoin(cellInd(1:66), ','); %// 254 characters
str2 = strjoin(cellInd(1:67), ','); %// 258 characters
hSheet.Range(str1).Interior.Color = 255; %// Works
hSheet.Range(str2).Interior.Color = 255; %// Error 0x800A03EC
hWB.Save;
hWB.Close(false);
hActX.Quit;
How can I get around this? I found no other relevant method of calling Range, or of otherwise getting the cells I want to modify.

Answer 1

If you start with a String, you can test its length to determine if Range() can handle it. Here is an example of building a diagonal range:
Sub DiagonalRange()
Dim BigString As String, BigRange As Range
Dim i As Long, HowMany As Long, Ln As String
HowMany = 100
For i = 1 To HowMany
BigString = BigString & "," & Cells(i, i).Address(0, 0)
Next i
BigString = Mid(BigString, 2)
Ln = Len(BigString)
MsgBox Ln
If Ln < 250 Then
Set BigRange = Range(BigString)
Else
Set BigRange = Nothing
arr = Split(BigString, ",")
For Each a In arr
If BigRange Is Nothing Then
Set BigRange = Range(a)
Else
Set BigRange = Union(BigRange, Range(a))
End If
Next a
End If
BigRange.Select
End Sub
For i = 10, the code will the the direct method, but if the code were i=100, the array method would be used.

Answer 2

The solution, as Rory pointed out, is to use the Union method. To minimize the number of calls from MATLAB to the ActiveX server, this is what I did:
str = strjoin(cellInd, ',');
isep = find(str == ',');
isplit = diff(mod(isep, 250)) < 0;
isplit = [isep(isplit) (length(str) + 1)];
hRange = hSheet.Range(str(1:(isplit(1) - 1)));
for ii = 2:numel(isplit)
hRange = hActX.Union(hRange, ...
hSheet.Range(str((isplit(ii-1) + 1):(isplit(ii) - 1))));
end
I used 250 in the mod to account for the cell names being up to 6 characters long, which is sufficient for me.