unable to evaluate viewState against Null

Question

This method I am using to fill the data source for a grid view, but for when getnew is false, it won't return any value , just returns a list with a single null value in it.

 private List<T> GetAll_T(bool getNew)
        {
            if (getNew)
                return (ViewState["T"] = Get_T()) as List<T>;
               //Get_T() returns a CustomList 
            return new List<T>
                {
                    ViewState["T"] != null ?
                    ViewState["T"] as T: 
                    (T)(ViewState["T"] = Get_T()) Collection
                };
        }

it gives me a warning for second line[when view state is null].expression is always false

why there is warning, when it's logically correct !

Answer 1

It is not clear from your code snippet what CustomerService.GetAllCustomer() returns.

You use it both like it returns a list on line(2) of the function and like it returns a single object on line(8).

I suggest writing it like this

private List<CustomerMaster> GetAllCustomer(bool getNew)
{
    if (getNew || null == ViewState["CustomerDataset"])
        ViewState["CustomerDataset"] = CustomerService.GetAllCustomer();
    return ViewState["CustomerDataset"] as List<CustomerMaster>;
}