C# datatable is null when trying to load excel

Question

I am using the ExcelDataReader extension to import excel files to C# datagridview. I am able to open the file and get it's sheets, but whenever I try to click on the sheet, My program breaks and says it's datatable is null. Please help me.

I am not sure if it's the var that is causing the problem, or that I didn't update the excel data into the datatable

  namespace Dashboard {
    public partial class Import_Excel : Form {
      public Import_Excel() {
        InitializeComponent();
      }
      DataSet result;

      private void btnLoad_Click(object sender, EventArgs e) {
        using (OpenFileDialog ofd = new OpenFileDialog()) {
          if (ofd.ShowDialog() == DialogResult.OK) {
            using (var stream = File.Open(ofd.FileName, FileMode.Open, FileAccess.Read)) {
              using (var reader = ExcelReaderFactory.CreateReader(stream)) {
                var result = reader.AsDataSet(new ExcelDataSetConfiguration() {
                  UseColumnDataType = true,
                  ConfigureDataTable = (data) => new ExcelDataTableConfiguration() {
                    UseHeaderRow = true
                  }
                });
                cboSheet.Items.Clear();
                DataTableCollection table = result.Tables;

                foreach (DataTable dt in result.Tables) {
                  cboSheet.Items.Add(dt.TableName);
                }
                reader.Close();
              }
            }
          }
        }
      }

      private void cboSheet_SelectedIndexChanged(object sender, EventArgs e) {
        dataGridView1.DataSource = result.Tables[cboSheet.SelectedIndex];
      }

      private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e) {
      }
    }
  }

score 1 · Answer 1 · answered Jan 15 '18 at 09:00

If method cboSheet_SelectedIndexChanged happens before btnLoad_Click() than result will be null thus result.Tables throws NullReferenceException

private void cboSheet_SelectedIndexChanged(object sender, EventArgs e)
{
  if(result != null) {
    dataGridView1.DataSource = result.Tables[cboSheet.SelectedIndex];
  }
}

Or just use: dataGridView1.DataSource = result?.Tables[cboSheet.SelectedIndex]; (will set it to null)

C# datatable is null when trying to load excel

1 Answers1