#1,205 – C# 6.0 – Using the Null-Conditional when Invoking a Delegate

When you fire an event (by invoking a delegate), you typically need to check for null before invocation.  This avoids a null reference exception if there are no subscribers to the event.

    public class Dog
        public Dog(string name, int age)
            Name = name;
            Age = age;

        public event EventHandler<string> NameChange;

        private string name;
        public string Name
            get { return name; }
                if (value != name)
                    name = value;

                    // Check for null before invocation
                    if (NameChange != null)
                        NameChange(this, name);

        public int Age { get; set; }

(The above pattern is not thread-safe).

An alternative pattern is to declare the event with a null handler, so that there is always at least one handler on the invocation list. (This is thread-safe).

In C# 6.0, we can use the null-conditional to invoke a delegate.

                    NameChange?.Invoke(this, name);

About Sean
Software developer in the Twin Cities area, passionate about software development and sailing.

4 Responses to #1,205 – C# 6.0 – Using the Null-Conditional when Invoking a Delegate

  1. Dominic says:

    Is the new NameChange?.Invoke(this, name); thread safe?

  2. I’ll point out that a common pattern is to do

    public event EventHandler NameChange = delegate {};

    this always adds an empty delegate to the handler and therefore no null check is necessary

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: