梳理Unity EventSystem事件系统调用过程

之前写过一个关于Button点击事件怎么被调用的,这次把EventSystem事件系统调用过程总结一下

在事件系统中,最重要的两个类是EventSystem与StandaloneInputModule,这两个类均继承自基类UIBehavior,而UIBehavior继承了MonoBehavior,因此这两个类是以组件的形式在Unity中执行逻辑的.

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   public abstract class UIBehaviour : MonoBehaviour
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   {
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   protected virtual void Awake()
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   {}
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   protected virtual void OnEnable()
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   {}
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   protected virtual void Start()
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    {}
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    protected virtual void OnDisable()
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    {}
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    protected virtual void OnDestroy()
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    {}
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    /// <summary>
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    /// Returns true if the GameObject and the Component are active.
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    /// </summary>
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    public virtual bool IsActive()
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    {
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    return isActiveAndEnabled;
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    }
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    #if UNITY_EDITOR
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    protected virtual void OnValidate()
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    {}
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    protected virtual void Reset()
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    {}
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    #endif
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    /// <summary>
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    /// This callback is called if an associated RectTransform has its dimensions changed. The call is also made to all child rect transforms, even if the child transform itself doesn't change - as it could have, depending on its anchoring.
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    /// </summary>
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    protected virtual void OnRectTransformDimensionsChange()
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    {}
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    protected virtual void OnBeforeTransformParentChanged()
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    {}
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    protected virtual void OnTransformParentChanged()
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    {}
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    protected virtual void OnDidApplyAnimationProperties()
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    {}
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    protected virtual void OnCanvasGroupChanged()
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    {}
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    /// <summary>
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    /// Called when the state of the parent Canvas is changed.
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    /// </summary>
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    protected virtual void OnCanvasHierarchyChanged()
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    {}
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    /// <summary>
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    /// Returns true if the native representation of the behaviour has been destroyed.
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    /// </summary>
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    /// <remarks>
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    /// When a parent canvas is either enabled, disabled or a nested canvas's OverrideSorting is changed this function is called. You can for example use this to modify objects below a canvas that may depend on a parent canvas - for example, if a canvas is disabled you may want to halt some processing of a UI element.
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    /// </remarks>
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    public bool IsDestroyed()
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    {
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    // Workaround for Unity native side of the object
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    // having been destroyed but accessing via interface
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    // won't call the overloaded ==
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    return this == null;
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    }
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    }

首先对于EventSystem,它其中有BaseInputModule m_CurrentInputModule与 List<BaseInputModule> m_SystemInputModules均是管理输入模块的,默认情况下Unity与含有EventSystem的物体一同生成StandaloneInputModule

对于EventSystem中List<BaseInputModule> m_SystemInputModules中的对象添加是在BaseInputModule类中

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   protected override void OnEnable()
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   {
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   base.OnEnable();
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   m_EventSystem = GetComponent<EventSystem>();
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   m_EventSystem.UpdateModules();
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   }
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   BaseInputModule中的OnEnable()方法
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    public void UpdateModules()
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    {
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    GetComponents(m_SystemInputModules);
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    for (int i = m_SystemInputModules.Count - 1; i >= 0; i--)
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    {
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    if (m_SystemInputModules[i] && m_SystemInputModules[i].IsActive())
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    continue;
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    m_SystemInputModules.RemoveAt(i);
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    }
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    }
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23.  
    EventSystem中的OnEnable()方法

在BaseInputModule调用EventSystem的UpdateModules方法之后将对List<BaseInputModule> m_SystemInputModules进行填充,而StandaloneInputModule继承自BaseInputModule且StandaloneInputModule与EventSystem在同一个物体上,因此StandaloneInputModule被加入到EventSystem中的List<BaseInputModule> m_SystemInputModules中之后进行轮询访问.

在EventSystem中其内部的Update方法进行帧调用每一个BaseInputModule对应的方法

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   protected virtual void Update()
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   {
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   if (current != this)
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   return;
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   TickModules();
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   bool changedModule = false;
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   for (var i = 0; i < m_SystemInputModules.Count; i )
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   {
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    var module = m_SystemInputModules[i];
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    if (module.IsModuleSupported() && module.ShouldActivateModule())
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    {
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    if (m_CurrentInputModule != module)
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    {
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    ChangeEventModule(module);
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    changedModule = true;
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    }
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    break;
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    }
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    }
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    // no event module set... set the first valid one...
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    if (m_CurrentInputModule == null)
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    {
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    for (var i = 0; i < m_SystemInputModules.Count; i )
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    {
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    var module = m_SystemInputModules[i];
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    if (module.IsModuleSupported())
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    {
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    ChangeEventModule(module);
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    changedModule = true;
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    break;
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    }
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    }
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    }
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    if (!changedModule && m_CurrentInputModule != null)
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    m_CurrentInputModule.Process();
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    }

这里current为EventSystem类,对于EventSystem一个场景只能存在一个,EventSystem被自身类静态存储      private static List<EventSystem> m_EventSystems = new List<EventSystem>();

对于TickModules方法,该方法进行轮询上述的BaseInputModule的对应方法

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   private void TickModules()
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   {
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   for (var i = 0; i < m_SystemInputModules.Count; i )
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   {
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   if (m_SystemInputModules[i] != null)
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   m_SystemInputModules[i].UpdateModule();
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   }
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   }

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   public override void UpdateModule()
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   {
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   if (!eventSystem.isFocused && ShouldIgnoreEventsOnNoFocus())
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   {
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   if (m_InputPointerEvent != null && m_InputPointerEvent.pointerDrag != null && m_InputPointerEvent.dragging)
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   {
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   ReleaseMouse(m_InputPointerEvent, m_InputPointerEvent.pointerCurrentRaycast.gameObject);
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   }
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    m_InputPointerEvent = null;
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    return;
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    }
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15.  
    m_LastMousePosition = m_MousePosition;
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    m_MousePosition = input.mousePosition;
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    }

对于EventSystem的Update方法中间部分则是为了确保该输入模块适应当前平台的保障

在EventSystem的Update方法最后执行了每个BaseInputModule的Process方法

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   public override void Process()
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   {
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   if (!eventSystem.isFocused && ShouldIgnoreEventsOnNoFocus())
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   return;
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   bool usedEvent = SendUpdateEventToSelectedObject();
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   // case 1004066 - touch / mouse events should be processed before navigation events in case
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   // they change the current selected gameobject and the submit button is a touch / mouse button.
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    // touch needs to take precedence because of the mouse emulation layer
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    if (!ProcessTouchEvents() && input.mousePresent)
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    ProcessMouseEvent();
14.  
     
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    if (eventSystem.sendNavigationEvents)
16.  
    {
17.  
    if (!usedEvent)
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    usedEvent |= SendMoveEventToSelectedObject();
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20.  
    if (!usedEvent)
21.  
    SendSubmitEventToSelectedObject();
22.  
    }
23.  
    }

其中SendUpdateEventToSelectedObject方法将EventSystem中之前被选中的物体执行Selected事件

之后若鼠标可用将执行处理鼠标事件的方法即ProcessMouseEvent

1.  
   protected void ProcessMouseEvent(int id)
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   {
3.  
   var mouseData = GetMousePointerEventData(id);
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   var leftButtonData = mouseData.GetButtonState(PointerEventData.InputButton.Left).eventData;
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   m_CurrentFocusedGameObject = leftButtonData.buttonData.pointerCurrentRaycast.gameObject;
7.  
    
8.  
   // Process the first mouse button fully
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   ProcessMousePress(leftButtonData);
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    ProcessMove(leftButtonData.buttonData);
11.  
    ProcessDrag(leftButtonData.buttonData);
12.  
     
13.  
    // Now process right / middle clicks
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    ProcessMousePress(mouseData.GetButtonState(PointerEventData.InputButton.Right).eventData);
15.  
    ProcessDrag(mouseData.GetButtonState(PointerEventData.InputButton.Right).eventData.buttonData);
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    ProcessMousePress(mouseData.GetButtonState(PointerEventData.InputButton.Middle).eventData);
17.  
    ProcessDrag(mouseData.GetButtonState(PointerEventData.InputButton.Middle).eventData.buttonData);
18.  
     
19.  
    if (!Mathf.Approximately(leftButtonData.buttonData.scrollDelta.sqrMagnitude, 0.0f))
20.  
    {
21.  
    var scrollHandler = ExecuteEvents.GetEventHandler<IScrollHandler>(leftButtonData.buttonData.pointerCurrentRaycast.gameObject);
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    ExecuteEvents.ExecuteHierarchy(scrollHandler, leftButtonData.buttonData, ExecuteEvents.scrollHandler);
23.  
    }
24.  
    }

GetMousePointerEventData方法是在抽象类PointerInputModule中,该方法进行组装鼠标指针数据,处理这一帧与上一帧的鼠标位置信息,以处理之后的拖拽事件,在组装数据时,先是组装了鼠标左键的数据,组装中还调用了EventSystem的RaycastAll方法,该方法得到该鼠标指针位置下所有射线模块能检测到的物体,之后对于鼠标右键与中键的数据是复制了鼠标左键的数据,之后进行返回该鼠标指针数据.

在得到鼠标指针数据之后ProcessMouseEvent进行各种鼠标事件调用,将调用类型与指针数据中的射线检测到的物体传递给ExecuteEvents,在ExecuteEvents中进行各种事件的触发

总结

EventSystem中保存所有输入模块,在EventSystem的Update方法中进行轮询每个输入模块的TickModules与Process方法,其中TickModules方法将EventSystem类中的保存的选中的对象进行触发Selected事件,保存的选中的对象可在Selected类中进行设置,之后在Process方法调用后进行组装鼠标指针数据,射线检测该指针下的物体,最后在ExecuteEvents中进行各种事件调用

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