什么是鉤子
之前有轉(zhuǎn)一篇關(guān)于回調(diào)函數(shù)的文章
鉤子函數(shù)、注冊(cè)函數(shù)、回調(diào)函數(shù),他們的概念其實(shí)是一樣的。
鉤子函數(shù),顧名思義,就是把我們自己實(shí)現(xiàn)的hook函數(shù)在某一時(shí)刻掛接到目標(biāo)掛載點(diǎn)上。
1. hook函數(shù),就是我們自己實(shí)現(xiàn)的函數(shù),函數(shù)類型與掛載點(diǎn)匹配(返回值,參數(shù)列表)
2. 掛接,也就是hook或者叫注冊(cè)(register),使得hook函數(shù)對(duì)目標(biāo)可用
3. 目標(biāo)掛載點(diǎn),也就是掛我們hook函數(shù)的地方(我們想在這個(gè)目標(biāo)點(diǎn)實(shí)現(xiàn)我們自己的功能)
先看一張圖:

hook的概念在windows的消息響應(yīng)機(jī)制里面體現(xiàn)的尤為明顯??赡芪覀兇蠹矣袑戇^windows桌面相關(guān)的程序(像MFC),里面有各種消息監(jiān)聽響應(yīng)機(jī)制。比如,要監(jiān)聽鼠標(biāo)左鍵是否按下這個(gè)事件,我們要去實(shí)現(xiàn)一個(gè)onLeftKeyDown()之類的方法,該方法可以稱為鉤子函數(shù)。同時(shí),我們還要去注冊(cè)鉤子函數(shù),MFC中是通過一組宏來實(shí)現(xiàn)的。這樣當(dāng)鼠標(biāo)左鍵按下后,就能調(diào)到我們定義的方法了。
為什么需要鉤子
大家思考一下上面這個(gè)例子,左鍵按下方法具體的邏輯是由框架自身去實(shí)現(xiàn),還是由我們用戶(調(diào)用者)去實(shí)現(xiàn)呢?顯然應(yīng)該由我們自己去實(shí)現(xiàn)。要提供通用的框架能力,框架自身去實(shí)現(xiàn)該方法功能,是沒有意義的,所以框架給提供一個(gè)掛載的point,把具體邏輯的實(shí)現(xiàn)交給用戶就好了,靈活可用。
鉤子使用
hook是一個(gè)編程機(jī)制,與語言無關(guān)。這里給個(gè)python的簡(jiǎn)單例子,幫助大家理解:
import timeclass LazyPerson(object): def __init__(self, name): self.name = name self.watch_tv_func = None self.have_dinner_func = None def get_up(self): print("%s get up at:%s" % (self.name, time.time())) def go_to_sleep(self): print("%s go to sleep at:%s" % (self.name, time.time())) def register_tv_hook(self, watch_tv_func): self.watch_tv_func = watch_tv_func def register_dinner_hook(self, have_dinner_func): self.have_dinner_func = have_dinner_func def enjoy_a_lazy_day(self): # get up self.get_up() time.sleep(3) # watch tv # check the watch_tv_func(hooked or unhooked) # hooked if self.watch_tv_func is not None: self.watch_tv_func(self.name) # unhooked else: print("no tv to watch") time.sleep(3) # have dinner # check the have_dinner_func(hooked or unhooked) # hooked if self.have_dinner_func is not None: self.have_dinner_func(self.name) # unhooked else: print("nothing to eat at dinner") time.sleep(3) self.go_to_sleep()def watch_daydayup(name): print("%s : The program ---day day up--- is funny!!!" % name)def watch_happyfamily(name): print("%s : The program ---happy family--- is boring!!!" % name)def eat_meat(name): print("%s : The meat is nice!!!" % name)def eat_hamburger(name): print("%s : The hamburger is not so bad!!!" % name)if __name__ == "__main__": lazy_tom = LazyPerson("Tom") lazy_jerry = LazyPerson("Jerry") # register hook lazy_tom.register_tv_hook(watch_daydayup) lazy_tom.register_dinner_hook(eat_meat) lazy_jerry.register_tv_hook(watch_happyfamily) lazy_jerry.register_dinner_hook(eat_hamburger) # enjoy a day lazy_tom.enjoy_a_lazy_day() lazy_jerry.enjoy_a_lazy_day()
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