Delegate pattern in Uniy3D

A-Delegate-pattern-in-Uniy3D.md

Delegate pattern in Uniy3D

• A delegate is something that acts on another thing's behalf.

• So if Thing A needed something, Thing B to Thing Z could deliver that to Thing A. This makes Things B to Z all delegates to Thing A. Thing A invokes a delegate function. Thing A doesn't care who runs the errand. Thing A doesn't care how it happens. As long as it happens.

Delegate Invoker

- A class that contains a Delegate Reference to a Delegate Function and can invoke it any time.

Delegate Reference

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/delegates/

- A type in C# that points to any function's address.

Delegate Function

- A function that can be invoked at any time. It's best for this function to be static, but
  it doesn't have to be.

Delegate Class - Contains one or many Delegate Functions. May be any type of class.

- Can be a Controller, Service or a Behaviour.

- Doesn't have to be attached to a GO.

- Define delegates in terms of functionality. 

- Naming format should be `"<Action>Delegate"`

This pattern allows you to assign different behaviors to a class. These behaviors are represented by delegates.

In this example, GameController will call a delegate to render some UI. But each scene needs to render UI a little bit differently. So I have defined a controller for each scene. The delegate's behavior is defined in this UI Controller.

Debug_UIController.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Debug_UIController : MonoBehaviour
{
  private GameController GameController;

  void Start()
  {
    GameController = GameObject.Find("GameController").GetComponent<GameController>();
    GameController.updateDebugDelegate = UpdateDebugUI;
  }
  void UpdateDebugUI()
  {
    //Do something only when in the editor
  }
}

GameController.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class GameController : MonoBehaviour {

	public delegate void UpdateUIDelegate();
	public UpdateUIDelegate updateUIDelegate;

	public delegate void UpdateDebugDelegate();
	public UpdateDebugDelegate updateDebugDelegate;

	void Update() {
#if DEBUG
		updateDebugDelegate();
#endif
		updateUIDelegate();
	}
}

World1_UIController.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class World1_UIController : MonoBehaviour
{
  private GameController GameController;

  void Start()
  {
    GameController = GameObject.Find("GameController").GetComponent<GameController>();
    GameController.updateUIDelegate = UpdateUI;
  }
  void UpdateUI()
  {
    //Do something
  }
}

World2_UIController.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class World2_UIController : MonoBehaviour
{
  private GameController GameController;

  void Start()
  {
    GameController = GameObject.Find("GameController").GetComponent<GameController>();
    GameController.updateUIDelegate = UpdateUI;
  }
  void UpdateUI()
  {
    //Do something else
  }
}