I have a problem with Gem Box Spreadsheet msi

Question

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Hello to everyone,
I have to do a Excel Manager with C# and i choose to use Gem Box Spreadsheet Free

C#

var ef = new ExcelFile();
            ef = ExcelFile.Load(File_Lettura);
            ExcelWorksheet ws = ef.Worksheets.ActiveWorksheet;

            int riga = 13;
            string s = (ws.Cells["B6"]).ToString();
            string[] r = s.Split('-');
            int c = 0;

            while (ws.Cells["B"+riga.ToString()].Value != null)
            {

                if (ws.Cells["F"+riga.ToString()].Value.ToString() != "")
                {
                    // add row
                    dgwFile.Rows.Add();

                    dgwFile.Rows[c].Cells[0].Value = r[0] + "-" + r[1] + "-" + ws.Cells["B"+riga.ToString()].Value.ToString();
                    dgwFile.Rows[c].Cells[1].Value = ws.Cells["D" + riga.ToString()].Value.ToString() + ws.Cells["G" + riga.ToString()].Value.ToString() + ws.Cells["H" + riga.ToString()].Value.ToString() + ws.Cells["I" + riga.ToString()].Value.ToString();
                    dgwFile.Rows[c].Cells[2].Value = ws.Cells["F" + riga.ToString()].Value.ToString();
                    dgwFile.Rows[c].Cells[3].Value = "0";
                    c++;
                }
                riga++;
            }

VS give me a problem at the first "IF" with error : An unhandled exception of type 'System.NullReferenceException' occurred.
I think the wrong rows are the first 3
thanks in advance :)

Posted 9-Jul-15 21:18pm

Member 11822400

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Mario Z · Accepted Answer · 2015-07-10T01:52:00

Hi, if I understood you correctly you have a problem here:

C#

if (ws.Cells["F"+riga.ToString()].Value.ToString() != "")

Well the first thing that comes to my mind is that this cell is null, so try the following:

C#

ExcelCell cell = ws.Cells["F" + riga.ToString()];
if (cell != null && cell.Value.ToString() != "")
{
    // ...

Now to add some pointers to your code:

1. You don't have to initialize new ExcelFile instance if you are loading an existing excel file. So instead of this:

C#

var ef = new ExcelFile();
ef = ExcelFile.Load(File_Lettura);

Just use this:

C#

var ef = ExcelFile.Load(File_Lettura);

2. You can access each column, row and cell with a name by providing a string or with an index by providing an int.
In other words, for example instead of this:

C#

int riga = 13;
ws.Cells["B" + riga.ToString()]

You can use this:

C#

// Notice I reduced "riga" value by 1 because all indexes start with 0, while the row's names start with "1".
int riga = 12; 
ws.Columns["B"].Cells[riga];

3. Why are you using while loop?
It's much easier and intuitive to iterate through the required group of cell.
For example instead of this:

C#

while (ws.Cells["B"+riga.ToString()].Value != null)

Use something like this:

C#

foreach (ExcelCell cell in ws.Cells.GetSubrange("B13", "B" + ws.Rows.Count))
{
    if (cell == null || string.IsNullOrEmpty(cell.Value.ToString()))
        continue;

    // Do the rest ...
}

4. Last what is dgwFile, is it Windows Form's DataGridView control?
In case it is check out this sample.
It shows how to use DataGridViewConverter.ExportToDataGridView and DataGridViewConverter.ImportFromDataGridView methods.