Question

I want do define an action that sets a property with a value (calculated by a worker thread). That action should be called in another thread context (UI thread).

To simplify the problem – it boils down to the question: why does this code don’t work and what do I have to do to make it work like intended:

    public struct Person
    {
        public string Name;
    }

    Person person;
    Action<Person> action;

    public void Update()
    {
        person = new Person();

        new Thread(() =>
        {
            action = new Action<Person>(c => c.Name = "Me");
        }).Start();

        Thread.Sleep(1000);
        action(person);

        Debug.WriteLine(person.Name ?? "null");
    }

Why is this giving me “null” instead of “Sami”?

Answer 1

The type Person is a struct. This means that when you pass person as an argument, a copy is made. So the action updates a copy, a not person itself. If you change Person to a class, you will see that your example works.

For more information about the difference between structs and classes, see what’s the difference between struct and class in .Net?