ios - 了解 NSBlockOperation

Question

我正在进入 NSBlockOperation 并且我有一些问题。值得注意的是，documentation对于 addExecutionBlock 说:

Discussion

The specified block should not make any assumptions about its execution environment.

Calling this method while the receiver is executing or has already finished causes an NSInvalidArgumentException exception to be thrown.

什么样的情况会抛出NSInvalidArgumentException？ “当接收者正在执行时”到底是什么意思？什么会导致这个？

Answer 1

当操作正在运行或已经完成时，您不能使用 addExecutionBlock: 添加执行 block 。就是这个意思。