Rule of write code with C# in Unity3d

Good Practice

1. 普通的Public变量可以在inspect里显示，变量是可以在inspect里赋值并realtime反映在被attach到的GameObject上的。注意经典public property的写法，在inspect里不会显示
2. You can't new MonoBehaviour, or override MonoBehabiour基类,不可以override Start和Update各种方法. Only public no argument constructor work, ignore fancy constructor.
3. 一般Unity下的初始值由Start()方法提供，而不是通过Constructor，如果非要写Constructor只可以用不带参数的而且不可以重载带不同参数的constructor(默认会变为不带参数的)。
4. Corotine是关于如何suspend 一个方法 in the game（防止该程序块执行时间过长拖慢整个game loop或者为了Asyn）, 以及访问WWW的技巧

MonoBehaviour Lifecycle function

• Awake()：
  • 当一个脚本实例被loaded into scene时Awake被调用，程序Dynamic添加或者手动Drag到GameObject上的script一旦load到scene里就开始Awake()。
  • Awake用于在游戏开始之前初始化变量或游戏状态。Awake在所有对象被初始化之后调用，所以你可以安全的与其他对象对话或用诸如GameObject.FindWithTag这样的函数搜索它们。
  • Each GameObject's Awake is called in a random order between objects. Because of this, you should use Awake to set up references between scripts, and use Start to pass any information back and forth.

  • private GameObject target;
        void Awake() {
            target = GameObject.FindWithTag("Player");
        }

  • Awake总是在Start之前执行。这允许你协调初始化顺序。
  • Awake不能用作co-routine.
  • •Will be called once after all prefab and GameObject is been instantiated
    •If a GameObject is in-active during start up Awake is not called until it is made active, or a function in any script attached to it is called.
    •Awake is called first even if the script component is not enabled and is best used for setting up any resources between scripts and initialization.

• Start()：
  • Start在behaviour的生命周期中只被调用一次，Start is only called if the script instance is enabled，调整Script启动与否可以控制初始化的时间。
  • 这是Initialize初始参数代替Constructor的地方。可以包含Coroutine方法.
• Awake VS Start

• FixedUpdate()：
  • 处理RigidBody相关的计算放这里，Call on fixed time interval（使用的原因是如果放到Update()里called once per farme，很多geometry被load的话主程序会Hang)。
  • 每一个game loop的时间长短可能不一样，取决于渲染每次loop的速度，所以一个fame里会被call几次game loop，FixedUpdate也就决定于这个次数，可能一个frame被call10次，也可能被call5次。在每个frame的FixedDetalTime等长的情况下比如50帧的画面即0.02/sec，有的渲染快的frame被call了5次FixedUpdate，有的渲染慢的frame被call了10次FixedUpdate
  • • is called before the first frame update only if the script instance is enabled.Start is called after Awake,immediately before the first Update,but only if the script component is enabled.
    •This means that you can use Start for anything you need to occur when the script component is enabled.This allows you to delay any part of your initialization code until it's really needed.
  • •Called more frequently than Update() , Used for physics GameObject
    •Fixed Update is called on a regular timeline and will have same time between calls
    •Used for regular updates such as adjusting physics (Rigibody) objects

• Update（）：
  • Been called every frame
  • •Most commonly used function in unity, Used for all Non-Physics GameObject
    •Called Every frame
    •Update is not called on a regular timeline. If one frame takes longer to process then the time between update calls will be different.

• Awake VS Start
• 

• LateUpdate（）：Call after all Update() function has been called，这可用于调整脚本执行顺序。比如：For example a follow camera should always be implemented in LateUpdate because it tracks objects that might have moved inside Update.

• OnEvent functions：called as part of reactions or event to different situations，见unity主页

Gameloop

Game Loop ex：点击Play, call Awake(),然后是Start()

　　每个frame可以有多次的gameloop，每次gameloop里先后执行

• • Any of On event(OnDisable OnEnable) -> Update() -> Coroutines() -> LateUpdate() -> GUI render, Camera Render (Continue the cycle)

• • 上面GameLoop里没有引入FixedUpdate()，因为其在固定的frame下call
  • WaitForFixedUpdate, WaitForEndOfFrame, and then WaitForSeconds是在Coroutines里被call的，不是每个loop都call，看其设定。
  • 所有的Coroutines都是建立在MonoBehivour下的，如果MonoBehivour destroy了后所有的Coroutines也将消失作。