Question

I want to be able to call a particular method automatically upon construction of a derived object, however I can’t think how to do it. The following code illustrates. Another answer recommended OnLoad, but I am doing this for Unity on Mac and OnLoad doesn’t appear to be supported by my platform. Any suggestions?

public class Parent {

    public Parent ()
    {
        // A. Stuff to do before child constructor code runs
        DoThisAutomaticallyAfterConstruction();
    }

    public void DoThisAutomaticallyAfterConstruction()
    {
        // C. In this example, this will run after A, before B. I want it to run ABC
    }
}

public class Child : Parent {

    public Child () : base()
    {
        // B. Stuff to do here after parent constructor code runs
    }
}

Answer 1

Unfortunately there’s no built-in way to do what you want (it’s a fairly-often-requested feature).

One workaround is to implement a factory pattern, where you don’t create objects by calling the constructor directly, but instead implement a static method to create them for you. For example:

public class MyClass
{
  public MyClass()
  {
    // Don't call virtual methods here!
  }

  public virtual void Initialize()
  {
    // Do stuff -- but may be overridden by derived classes!
  }
}

then add:

public static MyClass Create()
{
  var result = new MyClass();

  // Safe to call a virtual method here
  result.Initialize();

  // Now you can do any other post-constructor stuff

  return result;
}

and instead of doing

var test = new MyClass();

you can do

var test = MyClass.Create();