


Introduction
The observer pattern defines one-to-many dependencies of objects, so that when an object changes state, all its dependents will be notified and automatically updated!
Design principles
In the observer In mode, what changes is the status of the subject and the number of observers. Using this pattern, you can change objects that depend on the theme's state without changing the theme. ——Find out the changing aspects of the program, and then separate them from the fixed aspects!
Both the subject and the observer use interfaces: the observer uses the subject's interface to register with the subject, and the subject uses the observer interface Notify observers. This allows the two to operate normally while having the advantage of loose coupling! ——For interface programming, not implementation programming!
.
The observer pattern uses "composition" to combine many observers into a theme. This relationship between objects (observers - subjects) is not generated through inheritance, but through composition at runtime. ——Use more combination and less inheritance!
Code
/**
* Observer Pattern
* @author: Mac
* @date: 2012/02/22
* /
class Paper{ /* Topic*/
private $_observers = array();
public function register($sub){ /* Register observers*/
$this->_observers [] = $sub;
}
public function trigger(){ /* External unified access*/
if(!empty($this->_observers)){
foreach($this ->_observers as $observer){
$observer->update();
}
}
}
}
/**
* The interface to be implemented by the observer
*/
interface Observerable{
public function update();
}
class Subscriber implements Observerable{
public function update(){
echo "Callbackn";
}
}
//The following is the test code
?
/* Test*/
$paper = new Paper();
$paper->register(new Subscriber());
//$paper->register(new Subscriber1());
//$paper->register(new Subscriber2());
$paper->trigger();
Summary
When a new object is to be filled in, it only needs to be registered in the subject (also called an observable) (there are many ways to register, you can also do it during construction , or register in the interface accessed by the framework), and then implement the code directly in the interface of the new object. This reduces the coupling between subject and observer objects.
Good design patterns don’t go directly into your code, they go into your brain.

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。


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