Question

how to limit the number of continuous ‘comma’ in a textbox?…ex it should not allow user to enter more than 2 comma continuously

Answer 1

This should handle most scenarios, I believe:

private void TextBox_TextChanged(object sender, EventArgs e)
{
    TextBox tb = sender as TextBox;
    if (tb != null)
    {
        int pos = tb.SelectionStart;
        int length = tb.Text.Length;
        tb.Text = tb.Text.Replace(",,", ",");
        int diff = length- tb.Text.Length;
        tb.SelectionStart = pos == 0 || diff == 0 ? pos : pos - diff;
    }
}

This works when you type text into the TextBox, as well as when you paste text into it.