The following code snippet was highlighted in Visual Studio alongside a suggestion for simplifying it.
if ( drawMethodsDelegate != null )
drawMethodsDelegate ( e.Graphics );
When I clicked on the lightbulb suggestion thing, Visual Studio refactored it into the following
drawMethodsDelegate?.Invoke ( e.Graphics );
And no. The question mark is not a typo. I don't understand what the question mark is used for and I can't find anything relevant on MSDN. I also looked at the Tutorial Point Delegates page but found no useful information.
Tutorial Point page , MSDN Delegates page , MSDN Control.Invoke page
This is the null conditional operator.
drawMethodsDelegate?.Invoke ( e.Graphics );
Provided that drawMethodsDelegate is not null calls the Invoke method. It is an operator that being introduced in the 6th version of C# and you can see it as a syntactic sugar, which helps you to write less code for handling null checks.
Last but not least, the above check is also thread-safe !
For further info please have a look here
This is a null condition operator that came with C# 6.0
https://msdn.microsoft.com/en-us/library/dn986595.aspx
it means IF drawMethodsDelegate is not null Invoke the method else do nothing.