React生命周期中的componentWillReceiveProps

Question

http://reactjs.cn/react/docs/...
讲到componentWillReceiveProps的时候底下有一个注意事项
不太理解这段话的意思?
One common mistake is for code executed during this lifecycle method to assume that props have changed. To understand why this is invalid, read A implies B does not imply B implies A
There is no analogous method componentWillReceiveState. An incoming prop transition may cause a state change, but the opposite is not true. If you need to perform operations in response to a state change, use componentWillUpdate.

Answer 1

意思是说只要上一级组件的render()发生，这个callback就会被调用。
如果props改变则会被调用 不能说明 调用的原因一定是props的改变，有可能不变。