写在最前面
或许对于大部分Unity3D程序员来说，第一次接触脚本编写的时候都是从MonoBehavior开始的。MonoBehavior是Uniy3d脚本编写核心的类之一， 它预先定义好了很多事件，并且这些事件按照预先定义好顺序执行。了解MonoBehavior提供的这些事件的执行顺序，是我们进一步提高脚步编程和了解Unity3D内部逻辑的必要一步。我们先从MonoBehavior提供的事件说起。
MonoBehavior都提供了什么事件
MonoBehavior提供的事件从编辑器到游戏结束都有涉及。下面列举一些常用的，更详列表可以参照 这个页面。
与编辑相关
| 名称 | 注释 |
|---|---|
| Reset | Reset to default values. |
Update相关
| 名称 | 注释 |
|---|---|
| FixedUpdate | This function is called every fixed framerate frame, if the MonoBehaviour is enabled. |
| Update | Update is called every frame, if the MonoBehaviour is enabled. |
| LateUpdate | LateUpdate is called every frame, if the Behaviour is enabled. |
生命周期相关
| 名称 | 注释 |
|---|---|
| Awake | Awake is called when the script instance is being loaded. |
| OnEnable | This function is called when the object becomes enabled and active. |
| OnDisable | This function is called when the behaviour becomes disabled () or inactive. |
| OnDestroy | This function is called when the MonoBehaviour will be destroyed. |
| OnApplicationFocus | Sent to all game objects when the player gets or loses focus. |
| OnApplicationPause | Sent to all game objects when the player pauses. |
| OnApplicationQuit | Sent to all game objects before the application is quit. |
| Start | Start is called on the frame when a script is enabled just before any of the Update methods is called the first time. |
物理系统相关
| 名称 | 注释 |
|---|---|
| OnCollisionEnter | OnCollisionEnter is called when this collider/rigidbody has begun touching another rigidbody/collider. |
| OnCollisionStay | OnCollisionStay is called once per frame for every collider/rigidbody that is touching rigidbody/collider. |
| OnCollisionExit | OnCollisionExit is called when this collider/rigidbody has stopped touching another rigidbody/collider. |
| OnCollisionEnter2D | Sent when an incoming collider makes contact with this object’s collider (2D physics only). |
| OnCollisionStay2D | Sent each frame where a collider on another object is touching this object’s collider (2D physics only). |
| OnCollisionExit2D | Sent when a collider on another object stops touching this object’s collider (2D physics only). |
| OnTriggerEnter | OnTriggerEnter is called when the Collider other enters the trigger. |
| OnTriggerStay | OnTriggerStay is called once per frame for every Collider other that is touching the trigger. |
| OnTriggerExit | OnTriggerExit is called when the Collider other has stopped touching the trigger. |
| OnTriggerEnter2D | Sent when another object enters a trigger collider attached to this object (2D physics only). |
| OnTriggerStay2D | Sent each frame where another object is within a trigger collider attached to this object (2D physics only). |
| OnTriggerExit2D | Sent when another object leaves a trigger collider attached to this object (2D physics only). |
输入系统相关
| 名称 | 注释 |
|---|---|
| OnMouseDown | OnMouseDown is called when the user has pressed the mouse button while over the GUIElement or Collider. |
| OnMouseOver | OnMouseOver is called every frame while the mouse is over the GUIElement or Collider. |
| OnMouseUp | OnMouseUp is called when the user has released the mouse button. |
| OnMouseDrag | OnMouseDrag is called when the user has clicked on a GUIElement or Collider and is still holding down the mouse. |
| OnMouseEnter | OnMouseEnter is called when the mouse entered the GUIElement or Collider. |
| OnMouseExit | OnMouseExit is called when the mouse is not any longer over the GUIElement or Collider. |
| OnMouseUpAsButton | OnMouseUpAsButton is only called when the mouse is released over the same GUIElement or Collider as it was pressed. |
渲染相关
| 名称 | 注释 |
|---|---|
| OnPreCull | OnPreCull is called before a camera culls the scene. |
| OnBecameVisible | OnBecameVisible is called when the renderer became visible by any camera. |
| OnBecameInvisible | OnBecameInvisible is called when the renderer is no longer visible by any camera. |
| OnWillRenderObject | OnWillRenderObject is called once for each camera if the object is visible. |
| OnPreRender | OnPreRender is called before a camera starts rendering the scene. |
| OnRenderObject | OnRenderObject is called after camera has rendered the scene. |
| OnPostRender | OnPostRender is called after a camera finished rendering the scene. |
| OnRenderImage | OnRenderImage is called after all rendering is complete to render image. |
| OnGUI | OnGUI is called for rendering and handling GUI events. |
| OnDrawGizmos | Implement OnDrawGizmos if you want to draw gizmos that are also pickable and always drawn. |
用图来表示MonoBehavior事件执行顺序
总结:
- 首次加载场景时执行Awake()
- Start()只在第一帧才执行, Start()在Awake()之后执行
- Update的执行顺序是: FixedUpdate() -> Update() -> LateUpdate()
- 以每一帧的Update()事件作分界线：
- Update()之前：物理系统和输入系统相关事件先执行，如OnTriggerXXX和OnMouseXXX事件。此处XXX是占位符，如OnTriggerXXX可以代表OnTriggerEnter或者OnTriggerExit
- Update()之后：场景渲染和协程，如OnRenderImage()和yield WWW语句
- 协程中，除了WaitForFixedUpdate是在FixedUpdate之后，Update之前执行，其他的都是在Update之后，场景渲染前执行
- GUI事件OnGUI在场景渲染完之后执行
- 当对象被销毁时执行OnDestory()事件
- 当游戏退出时执行OnApplicationQuit()
- OnEnable()和OnDisable()
- OnEnable()只有在Object是Active的状态下才能用，一般是Object被初始化或者Object从disable到active过程中被调用
- OnDisable()只有到Object从active到disable状态才被调用
