Question

I have a problem here because my coding is not working(error) and I don’t know how to correct it.Can you guys check if this statement right or wrong? My conditions is
1)if textbox productname is null or empty and dropdownlist1 not selected, text will null.
2)if textbox productname is filled(string) then text will filled in
3)if if textbox productname is null or empty and dropdownlist1 selected, text will select value.
Refer bold text.THANKS!!

if (String.IsNullOrEmpty(txtSearchProductname.Text) == true)
    {
        if (**DropDownList1.SelectedValue.ToString == null**)
        {
            txtSearchProductname.Text = " ";
        }
        else 
        {
            SqlProductmaster.InsertParameters["ProductName"].DefaultValue = DropDownList1.SelectedValue.ToString();
        }                
     }
    else 
    {
        SqlProductmaster.InsertParameters["ProductName"].DefaultValue = txtProductName.Text.ToString();
    }

Answer 1

Two issues:

1. You have ToString, not ToString(). ToString refers to the function itself; you need the parentheses to invoke the method
2. You should not be calling ToString() at all, since the value may be null; this will generate a NullReferenceException. Just check if DropDownList1.SelectedValue == null.

This should be all you need:

if (String.IsNullOrEmpty(txtSearchProductname.Text))
{
    if (DropDownList1.SelectedValue == null)
    {
        txtSearchProductname.Text = " ";
    }
    else 
    {
        SqlProductmaster.InsertParameters["ProductName"].DefaultValue = DropDownList1.SelectedValue;
    }                
 }
else 
{
    SqlProductmaster.InsertParameters["ProductName"].DefaultValue = txtProductName.Text;
}