Cannot perform runtime binding on a null reference - Empty Excel Cells

问题

I cannot seem to think of a way to correct the error mentioned in the title and was looking for some ideas on what should be done.

I am trying to read the rows of a excel spreadsheet into an object.

The first time it loops I have no problems because row 1, column 1 and row 1 column 2 have data in them.

But when it gets to row 2, column 1 and row 2 column 2 it falls over with the above error because those cells in spreadsheet are "empty"

I just cannot work out where I can put some "if null" checks in.

Can anyone suggest how to do it please?

Here is my code...

private static void IterateRows(Excel.Worksheet worksheet)
    {
        //Get the used Range
        Excel.Range usedRange = worksheet.UsedRange;

        // create an object to store the spreadsheet data
        List<SPREADSHEETModel.spreadsheetRow> spreadsheetrows = new List<SPREADSHEETModel.spreadsheetRow>();

        //Iterate the rows in the used range
        foreach (Excel.Range row in usedRange.Rows)
        {
            for (int i = 0; i < row.Columns.Count; i++)
            {
                spreadsheetrows.Add(new SPREADSHEETModel.spreadsheetRow()
                {
                    col1 = row.Cells[i + 1, 1].Value2.ToString(),
                    col2 = row.Cells[i + 1, 2].Value2.ToString()
                });
            }
        }
    }

回答1:

Do not use .ToString() it will cause null reference exception when the value is null. Use Convert.ToString(), it will return empty string for the null value.

col1 = Convert.ToString(row.Cells[i + 1, 1].Value2);
col2 = Convert.ToString(row.Cells[i + 1, 2].Value2);

回答2:

You need them before the call to ToString. Maybe you can even move if before the adding, since I think it isn't useful to add empty rows, but that might nog be true in your scenario:

if (row.Cells[i + 1, 1].Value2 != null && row.Cells[i + 1, 2].Value2 != null)
{
    spreadsheetrows.Add(new SPREADSHEETModel.spreadsheetRow()
    {
        col1 = row.Cells[i + 1, 1].Value2.ToString(),
        col2 = row.Cells[i + 1, 2].Value2.ToString()
    });
}

Otherwise this is probably what you need:

col1 = row.Cells[i + 1, 1].Value2 != null ? row.Cells[i + 1, 1].Value2.ToString() : null,

The reason behind the exception is that Value2 is a dynamic, so the return value is determined on runtime. And if Value2 is null, it can't determine the ToString method to call.

回答3:

You can check inside in for loop:

    //Iterate the rows in the used range
    foreach (Excel.Range row in usedRange.Rows)
    {
        for (int i = 0; i < row.Columns.Count; i++)
        {
            spreadsheetrows.Add(new SPREADSHEETModel.spreadsheetRow()
            {
        if (row.Cells[i + 1, 1].Value2 != null)
        {                       
            col1 = row.Cells[i + 1, 1].Value2.ToString();
        }
        if (row.Cells[i + 1, 2].Value2 != null)
        {
                        col2 = row.Cells[i + 1, 2].Value2.ToString();
        }
        if (row.Cells[i + 1, 3].Value2 != null)
        {
                        col3 = row.Cells[i + 1, 3].Value2.ToString();
        }
            });
        }
    }

来源：https://stackoverflow.com/questions/28235162/cannot-perform-runtime-binding-on-a-null-reference-empty-excel-cells

标签

.net

excel

vsto