返回一个布尔值指示调用该方法的对象是否取消了第一响应对象的状态。
Returns a Boolean value indicating whether the receiver is willing to relinquish first-responder status.
COM的客户程序通过获取指向一个对象接口的一个指针，并通过该指针来调用方法以实现与COM对象之间的互相作用，就好像对象驻留在客户程序的地址空间中一样。
A COM client interacts with a COM object by acquiring a pointer to one of the object's interfaces and invoking methods through that pointer, as if the object resides in the client's address space.
不会存在两个线程同时调用该对象的方法的情况（显然是以对象为基础的）。
No two threads will be able to execute methods against those objects at the same time (on a per-object basis, obviously).
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