Question

I want to do something like this but C# doesn’t accept this:

    public static void setPrice(Double? value)
    {

        if (value != null) {
            this.TextBoxPrice.Text = Math.Round(value, 2).ToString();
        } else {
            this.TextBoxPrice.Text = "No Price";   
        }

    }

So does it mean using nullable type Double? is completely useless in this use case ? What can I use then ?

Update: I made a mystypo I actually meant

    public static void setPrice(Double? value)

so I corrected.

Answer 1

You’re not currently using a nullable type – Double is a non-nullable value type, so can never be null. This is what you want:

public static void setPrice(Double? value)
{

    if (value != null) {
        this.TextBoxPrice.Text = Math.Round(value.Value, 2).ToString();
    } else {
        this.TextBoxPrice.Text = "No Price";   
    }
}

On the other hand, you should not be using a double to represent financial values. It’s inappropriate as a binary floating point type. Use decimal (or decimal?) instead.

(Note that Double? is equivalent to Nullable<Double>.)

If you’ve come from a Java background, you may be expecting Double to be a reference “wrapper” type to start with – it’s not. In C# double is simply an alias for System.Double; they’re the same type.