#Unity3D MonoBehaviourPopulateExtension & friends

GameObjectFindComponentExtension.cs

/// @creator: Slipp Douglas Thompson
/// @license: Public Domain per The Unlicense.  See <http://unlicense.org/>.
/// @purpose: More-flexible GO-tree searching for Components by type, configurable via `SearchExtent` enum arg.
/// @why: Because this functionality should be built-into Unity.
/// @usage: Call `this.gameObject.FindComponent<«component-type»>(«SearchExtent-type»);`.
/// @intended project path: Assets/Plugins/UnityEngine Extensions/GameObjectFindComponentExtension.cs
/// @interwebsouce: https://gist.github.com/capnslipp/ac26e38fce770b5c4594
 
using System;
using UnityEngine;



public static class GameObjectFindComponentExtension
{
	public enum SearchExtent {
		Local = 1,
		Ancestry, // you are part of your own ancestry
		Ancestors, // you are *not* your own ancestor
		Descendantry, // you are part of your own descendantry
		Descendants, // you are *not* your own descendant
		
		None = 0
	}
	
	public static Component FindComponent(this GameObject @this,
		Type componentType,
		SearchExtent extent=SearchExtent.Local
	)
	{
		if (@this == null)
			throw new ArgumentNullException("This extension method was called on a null object, which is not allowed.", "@this");
		
		string failMessageHead = null;
		Component foundComponent = SearchForComponent(@this, componentType, extent, out failMessageHead);
		
		if (foundComponent == null)
			Debug.LogWarning(failMessageHead+" "+@this.GetType()+".", @this);
		
		return foundComponent;
	}
	
	public static ComponentT FindComponent<ComponentT>(this GameObject @this,
		SearchExtent extent=SearchExtent.Local
	) where ComponentT : Component
	{
		return (ComponentT)FindComponent(@this, typeof(ComponentT), extent);
	}
	
	
	static Component SearchForComponent(
		GameObject localGameObject,
		Type componentType,
		SearchExtent extent,
		out string failMessageHead
	)
	{
		switch (extent) {
			case SearchExtent.Local:
				return SearchForComponentInLocal(localGameObject, componentType, out failMessageHead);
			case SearchExtent.Ancestry:
				return SearchForComponentInAncestry(localGameObject, componentType, out failMessageHead, skipLocal: false);
			case SearchExtent.Ancestors:
				return SearchForComponentInAncestry(localGameObject, componentType, out failMessageHead, skipLocal: true);
			case SearchExtent.Descendantry:
				return SearchForComponentInDescendantry(localGameObject, componentType, out failMessageHead, skipLocal: false);
			case SearchExtent.Descendants:
				return SearchForComponentInDescendantry(localGameObject, componentType, out failMessageHead, skipLocal: true);
			
			default:
				failMessageHead = null;
				return null;
		}
	}
	
	static Component SearchForComponentInLocal(
		GameObject localGameObject,
		Type componentType,
		out string failMessageHead
	)
	{
		Component foundComponent = localGameObject.GetComponent(componentType);
		
		if (foundComponent != null) {
			failMessageHead = null;
			return foundComponent;
		}
		else {
			failMessageHead = string.Format("No "+componentType+" assigned and unable to find one for this");
			return null;
		}
	}
	
	static Component SearchForComponentInAncestry(
		GameObject localGameObject,
		Type componentType,
		out string failMessageHead,
		bool skipLocal=false
	)
	{
		Transform searchTransform = localGameObject.transform;
		if (skipLocal)
			searchTransform = localGameObject.transform.parent;
		
		Component foundComponent = null;
		while (searchTransform != null) {
			foundComponent = searchTransform.GetComponent(componentType);
			
			if (foundComponent != null)
				break;
			
			searchTransform = searchTransform.parent;
		}
		
		if (foundComponent != null) {
			failMessageHead = null;
			return foundComponent;
		}
		else {
			failMessageHead = string.Format("Unable to find a "+componentType+" "+(skipLocal ? "" : "on or ")+"above this");
			return null;
		}
	}
	
	static Component SearchForComponentInDescendantry(
		GameObject localGameObject,
		Type componentType,
		out string failMessageHead,
		bool skipLocal=false
	)
	{
		failMessageHead = null;
		
		Component[] foundComponents = localGameObject.GetComponentsInChildren(componentType, includeInactive: true); // actually searches self and all descendents, despite the name
		foreach (Component oneComponent in foundComponents)
		{
			if (oneComponent.gameObject == localGameObject) {
				if (skipLocal)
					continue;
				else
					return oneComponent;
			}
			else { // non-local
				return oneComponent;
			}
		}
		
		failMessageHead = string.Format("Unable to find a "+componentType+" "+(skipLocal ? "" : "on or ")+"under this");
		return null;
	}
}

MonoBehaviourPopulateExtension.cs

/// @creator: Slipp Douglas Thompson
/// @license: Public Domain per The Unlicense.  See <http://unlicense.org/>.
/// @purpose: Populates fields at runtime with references to other components with a one-liner.  Use to provide more GO-tree searching capability and better performance (via caching) than GetComponent.
/// @why: Because this functionality should be built-into Unity.
/// @usage: Call `this.PopulateComponentField(ref this.«component-field», «SearchExtent-type»);` inside Awake() for each field to be populated.
/// 	Optionally, create an additional field of type `GameObjectFindComponentExtension.SearchExtent` and pass that into the PopulateComponentField<>() call in order to allow configuring the SerachExtent in the editor.
/// @intended project path: Assets/Plugins/UnityEngine Extensions/MonoBehaviourPopulateExtension.cs
/// @interwebsouce: https://gist.github.com/capnslipp/ac26e38fce770b5c4594
 
using System;
using UnityEngine;
using SearchExtent=GameObjectFindComponentExtension.SearchExtent;



public static class MonoBehaviourPopulateExtension
{
	public static void PopulateComponentField(this MonoBehaviour @this,
		Type componentType,
		ref Component field,
		SearchExtent extent=SearchExtent.Local,
		bool forceRepopulate=false
	)
	{
		if (@this == null)
			throw new ArgumentNullException("This extension method was called on a null object, which is not allowed.", "@this");
		
		if (field != null && !forceRepopulate)
			return;
		
		Component foundComponent = @this.gameObject.FindComponent(componentType, extent);
		
		if (foundComponent != null)
			field = foundComponent;
	}
	
	/// It is probably best to call from within Awake (as opposed to OnEnable or Start) so that its values are ready by the time OnEnable and Start happen.
	/// 	Although this means that another script creating this component (via AddComponent) doesn't have a chance to assign values it may know before we wastefully search out values, Unity doesn't provide us many other options—
	/// 		there is no AddComponentDisabled() equivalent, and
	/// 		Awake is our only chance to set these up before OnEnable (which is often used for repeatable setup logic requiring references to be ready).
	/// 	Awake also ensures that this heavy lifting is done synchronously before we render the first frame of a new scene, hopefully avoiding most in-action stutters.
	public static void PopulateComponentField<ComponentT>(this MonoBehaviour @this,
		ref ComponentT field,
		SearchExtent extent=SearchExtent.Local,
		bool forceRepopulate=false
	) where ComponentT : Component
	{
		Component fieldStandin = field;
		PopulateComponentField(@this, typeof(ComponentT), ref fieldStandin, extent, forceRepopulate);
		field = (ComponentT)fieldStandin;
	}
}

Ω ExampleSomeOtherMB.cs

using UnityEngine;



public class ExampleSomeOtherMB : MonoBehaviour
{
	public int foo = 26;
}

Ω ExampleUsage.cs

/// @requires `HideInNormalInspector.cs`, from https://gist.github.com/capnslipp/8138106

using UnityEngine;
using SearchExtent=GameObjectFindComponentExtension.SearchExtent;



public class ExampleUsage : MonoBehaviour
{
	public BoxCollider boxCollider;
	[HideInNormalInspector] public SearchExtent boxCollider_SearchExtent = SearchExtent.Local;
	
	public ExampleSomeOtherMB someOtherMB;
	[HideInNormalInspector] public SearchExtent someOtherMB_SearchExtent = SearchExtent.Descendantry;
	
	
	void Awake()
	{
		this.PopulateComponentField(ref this.boxCollider, this.boxCollider_SearchExtent);
		this.PopulateComponentField(ref this.someOtherMB, this.someOtherMB_SearchExtent);
	}
	
	
	void Update()
	{
		// @fillin: Do werk here using `this.boxCollider` and `this.someOtherMB`.
	}
}

Ω Example MonoBehaviourPopulateExtension.unitypackage

Ω example-usage.part-1.edit-mode.png

Ω example-usage.part-2.play-mode.png