__isset和__unset:

这两个拦截方法被调用的规则和__get()和__set()非常类似，只是用于类中不存在或不可见属性被isset()和unset()两个全局方法应用时才会被分别触发。 

 

<?php
class TestClass {
private $privateField;
public $publicField;
public function __construct() {
$this->privateField = "Defined private field";
$this->publicField = "Defined public field";
}
public function __isset($property) {
print "__isset is called.\n";
return isset($this->$property);
}
public function __unset($property) {
print "__unset is called.\n";
if (isset($this->$property)) {
unset($this->$property);
}
}
}

$testObj = new TestClass();
print 'isset($testObj->privateField) is '.(isset($testObj->privateField) ? "true" : "false")."\n";
print 'isset($testObj->undefinedField) is '.(isset($testObj->undefinedField) ? "true" : "false")."\n";
print 'isset($testObj->publicField) is '.(isset($testObj->publicField) ? "true" : "false")."\n";

print "After unset......\n";
//下面两个函数调用后，$testObj的两个对象属性均会变为不可用。
//另外从输出结果来看，__unset方法仅仅被调用一次，因为publicField为可见属性，所以__unset不会因该属性而被调用。
unset($testObj->privateField);
unset($testObj->publicField);

print 'isset($testObj->privateField) is '.(isset($testObj->privateField) ? "true" : "false")."\n";
print 'isset($testObj->publicField) is '.(isset($testObj->publicField) ? "true" : "false")."\n";