How To Properly Use ?? With Default Values

Let’s define a nullable.  You can declare a variable as nullable, for example

int
? x;

You are saying that the int might have a value, or it might have a null value.  This is convenient

Now in your code you might want to check and see if its actually null and if it is, give it some default Value.  There is a shortcut for this in C# which is ??.  The ?? shortcut does not apply only to nullable values.  You can use it with anything that may be null.

Here is an example of how to use it.  In the following case, our ViewState for the key "readonly" might be null (i.e. we did not put anything in there yet), and we want to get a default value of true if it is null.  Here is how we can cast it

CS0019: Operator '??' cannot be applied to operands of type 'bool' and 'bool'

bool)(ViewState["readonly"]) ?? true;

myName.Visible = IsNothing(ViewState("readonly"))

myString = IIf(IsNothing(ViewState("isAdude")), "dude!" , "not a dude!")