How do you check for nullable value in an if statement

Question

I have the following code:

string thing="";
if(request.Session.Attributes?.TryGetValue("varName", out thing))
{
  //do stuff
}

request.Session.Attributes is a dictionary.

I understand that you can't have if(bool?) which is what the above does. I also know that you can have .GetValueOrDefault() so that null will be treated as false. But I can't do request.Session.Attributes?.GetValueOrDefault().TryGetValue("varName", out thing) So what is the correct way to return false if Attributes is null otherwise return the bool from the TryGetValue?

Answer 1

A quick and slightly dirty way is doing:

string thing="";
if(request.Session.Attributes?.TryGetValue("varName", out thing) ?? false)
{
  //do stuff
}

In this way you are sure that if Attributes is null, the second branch of the ?? will be chosen and it will not get inside the if.

Personally, I would split it, as having it in a 1-liner does not improve the code that much. It'd become:

string thing="";
var attributes = request.Session.Attributes; 
if(attributes != null && attributes.TryGetValue("varName", out thing))
{
  //do stuff
}

This is much more readable. Sometimes it is just fair to avoid using new features of the language if they do not improve the code.

Bonus tip: You can get a line back removing the declaration of things and placing it just after the out 😉: attributes.TryGetValue("varName", out string thing)