C# Excel VSTO can not convert string to String.Array

Question

I am new to VSTO C# excel add-in. I am looking to find total count of not null/empty rows in a range. My Code looks at the range "A4:E4" and count total number of rows.

This is the code :

private void button1_Click(object sender, RibbonControlEventArgs e)
        {
            Workbook workbook =  Globals.ThisAddIn.GetWorkBook("c:\\temp\\testfile.xlsx");
            Worksheet mergeSheet = workbook.Worksheets["Data"];
            Excel.Range mergeCells = mergeSheet.Range["A4:E4"];
            var colValues = (System.Array)mergeCells.Columns[1].Cells.Value;
            var strArray = colValues.OfType<object>().Select(o => o.ToString()).ToArray();
            var rowCount = strArray.Length;
        }

 [public Excel.Workbook GetWorkBook(string pathName)
        {
            return (Excel.Workbook)Application.Workbooks.Open(pathName);
        }][1]

I get error var colValues = (System.Array)mergeCells.Columns[1].Cells.Value; on line :

Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'Cannot convert type 'string' to 'System.Array''

It works when I have two rows in my range. I have hardcoded range A4:E4 to produce the error. My excel sheet (testfile.xlsx) looks like below:

Any ideas how do I resolve this?

Same line of code works when I have two rows. Eg and following line is updated

Excel.Range mergeCells = mergeSheet.Range["A4:E5"];

Answer 1

This line is causing me trouble, var colValues = (System.Array)mergeCells.Columns[1].Cells.Value

This row has only one value. Note that same line works when mergeCells range has two rows.

Why it does not work for single cell range:

The Value of a single cell is not an array (it's a Long, String, DateTime, etc.) and won't be cast to an array in that manner. You can see this by testing like below:

var myArray = (System.Array)"hello"

This will give same failure for other types:

Why it works for multi-cell range:

The Value of a multi-cell range will return a variant array of the individual cell values, which either is, or can be cast to a System.Array

There may be a better resolution, but at least you should be able to do like:

var colValues;
if (mergeCells.Columns[1].Cells.Count > 1)
{
    colValues = (System.Array)mergeCells.Columns[1].Cells.Value;
}
else
{
    // NB: you may need to cast other data types to string
    //     or you could use .Cells[0].Text.Split()
    colValues = (System.Array)mergeCells.Columns[1].Cells[0].Value.Split();
}

Answer 2

The problem is that Range.Value can return different types of objects. Among others, it can return

• a single value of type String , if the range contains a single cell containing a string or
• an array of values, if the range contains more than one cell.

The simplest solution would be to count the number of cells and "wrap" the special "single value" case in an array:

var range = mergeCells.Columns[1].Cells;
var values = (range.Count == 1)
    ? new object[] { range.Value })
    : ((Sytem.Array)range.Value).Cast<object>();