DataGridView Column header click error: the object reference does not point to an instance of the object

Hi RPA,

There are two different event for Cell Click and Header Click.

You need to handle both the events as per your requirement.

For Cell Click the event is CellClick (DataGridViewCellEventArgs).

For Header Click the event is ColumnHeaderMouseClick (DataGridViewCellMouseEventArgs).

Check this example. Now please take its reference and correct your code.

C#

public Form1()
{
    InitializeComponent();
    BindGrid();
}

private void BindGrid()
{
    string constring = ConfigurationManager.ConnectionStrings[1].ConnectionString;
    using (SqlConnection con = new SqlConnection(constring))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT Name,Country FROM Customers", con))
        {
            cmd.CommandType = CommandType.Text;
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                using (DataSet ds = new DataSet())
                {
                    sda.Fill(ds);
                    spGrid.DataSource = ds.Tables[0];
                    spGrid.AllowUserToAddRows = false;
                }
            }
        }
    }
}

private void dataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
{
    if (e.RowIndex > -1)
    {
        if (string.IsNullOrEmpty(spGrid.CurrentRow.Cells[e.ColumnIndex].Value.ToString()))
        {
            MessageBox.Show("cell is free");
        }
        else
        {
            MessageBox.Show("cell is not free");
        }
    }
}

private void spGrid_ColumnHeaderMouseClick(object sender, DataGridViewCellMouseEventArgs e)
{
    if (string.IsNullOrEmpty(spGrid.CurrentRow.Cells[e.ColumnIndex].Value.ToString()))
    {
        MessageBox.Show("cell is free");
    }
    else
    {
        MessageBox.Show("cell is not free");
    }
}

VB.Net

Public Sub New()
    InitializeComponent()
    BindGrid()
End Sub

Private Sub BindGrid()
    Dim constring As String = ConfigurationManager.ConnectionStrings(1).ConnectionString
    Using con As SqlConnection = New SqlConnection(constring)
        Using cmd As SqlCommand = New SqlCommand("SELECT Name,Country FROM Customers", con)
            cmd.CommandType = CommandType.Text
            Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                Using ds As DataSet = New DataSet()
                    sda.Fill(ds)
                    spGrid.DataSource = ds.Tables(0)
                    spGrid.AllowUserToAddRows = False
                End Using
            End Using
        End Using
    End Using
End Sub

Private Sub dataGridView1_CellClick(ByVal sender As Object, ByVal e As DataGridViewCellEventArgs)
    If e.RowIndex > -1 Then
        If String.IsNullOrEmpty(spGrid.CurrentRow.Cells(e.ColumnIndex).Value.ToString()) Then
            MessageBox.Show("cell is free")
        Else
            MessageBox.Show("cell is not free")
        End If
    End If
End Sub

Private Sub spGrid_ColumnHeaderMouseClick(ByVal sender As Object, ByVal e As DataGridViewCellMouseEventArgs)
    If String.IsNullOrEmpty(spGrid.CurrentRow.Cells(e.ColumnIndex).Value.ToString()) Then
        MessageBox.Show("cell is free")
    Else
        MessageBox.Show("cell is not free")
    End If
End Sub

Screenshot