UGUI学习手记-ExecuteEvents & EventInterface

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关于源码

关于源码可以参考这篇博客下载或调试。

EventInterface

代码分析

声明了一系列的 Event 事件

• IEventSystemHandler

• IPointerEnterHandler : IEventSystemHandler

• IPointerExitHandler: IEventSystemHandler

• IPointerDownHandler: IEventSystemHandler

• IPointerUpHandler: IEventSystemHandler

• IPointerClickHandler: IEventSystemHandler

• IBeginDragHandler: IEventSystemHandler

• IInitializePotentialDragHandler: IEventSystemHandler

• IDragHandler: IEventSystemHandler

• IEndDragHandler: IEventSystemHandler

• IScrollHandler: IEventSystemHandler

• IUpdateSelectedHandler: IEventSystemHandler

• ISelectHandler: IEventSystemHandler

• IDeselectHandler: IEventSystemHandler

• IMoveHandler: IEventSystemHandler

• ISubmitHandler: IEventSystemHandler

• ICancelHandler: IEventSystemHandler

以上这些接口都会在 ExecuteEvents 里被调用。 ExecuteEvents 类是个 静态类，不能被实例化，所有的公共方法都通过 ExecuteEvents.XXXX 来调用。

ExecuteEvents 里声明了一个 delegate 的类型EventFunction，这是一个泛型委托，委托的第一个参数 handler 可以是不同的类型。

public delegate void EventFunction<T1>(T1 handler, BaseEventData eventData);

然后对 EventInterface 里除了 IEventSystemHandler 外每一个接口声明了一个 EventFunction 类型的委托变量和方法。
形如：

private static void Execute(IPointerEnterHandler handler, BaseEventData eventData)
{
handler.OnPointerEnter(ValidateEventData<PointerEventData>(eventData));
}

ExecuteEvents

外部统一通过 Execute 方法执行事件, 本质 其实就是 指定某个接口类型，由Execute方法调用目标对象的接口方法 。

public static bool Execute<T>(GameObject target, BaseEventData eventData, EventFunction<T> functor) where T : IEventSystemHandler
{
var internalHandlers = s_HandlerListPool.Get();
GetEventList<T>(target, internalHandlers);
// if (s_InternalHandlers.Count > 0)
// Debug.Log("Executinng " + typeof (T) + " on " + target);
for (var i = 0; i < internalHandlers.Count; i++)
{
T arg;
try
{
arg = (T)internalHandlers[i];
}
catch (Exception e)
{
var temp = internalHandlers[i];
Debug.LogException(new Exception(string.Format("Type {0} expected {1} received.", typeof(T).Name, temp.GetType().Name), e));
continue;
}
try
{
functor(arg, eventData);
}
catch (Exception e)
{
Debug.LogException(e);
}
}
var handlerCount = internalHandlers.Count;
s_HandlerListPool.Release(internalHandlers);
return handlerCount > 0;
}

举例说明

在BaseInputModule里

protected void HandlePointerExitAndEnter(PointerEventData currentPointerData, GameObject newEnterTarget)
{
// if we have no target / pointerEnter has been deleted
// just send exit events to anything we are tracking
// then exit
if (newEnterTarget == null || currentPointerData.pointerEnter == null)
{
for (var i = 0; i < currentPointerData.hovered.Count; ++i)
ExecuteEvents.Execute(currentPointerData.hovered[i], currentPointerData, ExecuteEvents.pointerExitHandler);
currentPointerData.hovered.Clear();
if (newEnterTarget == null)
{
currentPointerData.pointerEnter = newEnterTarget;
return;
}
}
// if we have not changed hover target
if (currentPointerData.pointerEnter == newEnterTarget && newEnterTarget)
return;
GameObject commonRoot = FindCommonRoot(currentPointerData.pointerEnter, newEnterTarget);
// and we already an entered object from last time
if (currentPointerData.pointerEnter != null)
{
// send exit handler call to all elements in the chain
// until we reach the new target, or null!
Transform t = currentPointerData.pointerEnter.transform;
while (t != null)
{
// if we reach the common root break out!
if (commonRoot != null && commonRoot.transform == t)
break;
ExecuteEvents.Execute(t.gameObject, currentPointerData, ExecuteEvents.pointerExitHandler);
currentPointerData.hovered.Remove(t.gameObject);
t = t.parent;
}
}
// now issue the enter call up to but not including the common root
currentPointerData.pointerEnter = newEnterTarget;
if (newEnterTarget != null)
{
Transform t = newEnterTarget.transform;
while (t != null && t.gameObject != commonRoot)
{
ExecuteEvents.Execute(t.gameObject, currentPointerData, ExecuteEvents.pointerEnterHandler);
currentPointerData.hovered.Add(t.gameObject);
t = t.parent;
}
}
}

中的 ExecuteEvents.Execute(t.gameObject, currentPointerData, ExecuteEvents.pointerEnterHandler);

其他方法

• GetEventChain – 获取target的所有父对象(包含自己)

• ExecuteHierarchy – 通过 GetEventChain 获取 target 列表后执行 Execute 方法。

• GetEventHandler – 遍历目标对象及其父对象，判断他们是否包含某个指定接口，如果包含则作为返回值返回。而判断方法是 CanHandleEvent ，通过 GetEventList 方法获取 target 上的 T 类型的组件列表，判断列表数量不为零。 GetEventHandler 主要在输入模块里被调用，用于获取某个输入事件的响应对象。