PHP object-oriented guide (6) Usage of __set() __get() __isset() __unset()_PHP tutorial

10. Application of the four methods __set() __get() __isset() __unset()
Generally speaking, always define the attributes of a class as private, which is more in line with realistic logic. However, the reading
and assignment operations on attributes are very frequent, so in PHP5, two functions "__get()" and "__set()" are predefined to get
and assign their attributes. , as well as the "__isset()" method for checking attributes and the "__unset()" method for deleting attributes.
In the previous section, we have set and obtained methods for each attribute. In PHP5, we are provided with special methods for setting and obtaining values ​​for attributes
, "__set()" and " __get()". These two methods do not exist by default.
They are manually added to the class. Like the constructor method (__construct()), they will only exist if they are added to the class.
You can add these two methods in the following way, of course you can also add them according to your personal style:
Code snippet

Copy code The code is as follows:

//__get() method is used to obtain private properties
private function __get($property_name){
if(isset($this->$property_name)) {
return($this->$property_name);
}else {
return(NULL);
}
//__set() method is used to set private properties
private function __set($property_name, $value){
$this->$property_name = $value;
}

__get() method: This method is used to obtain private members For attribute values, there is a parameter. The parameter is passed in the name of the
member attribute you want to get, and the obtained attribute value is returned. This method does not need to be called manually, because we can also make the
method Private methods are automatically called by the object when private properties are directly obtained. Because the private attributes have been
encapsulated, the value cannot be obtained directly (for example: "echo $p1->name" is wrong to obtain directly),
but if you add With this method, when you use a statement such as "echo $p1->name" to directly obtain the value
, the __get($property_name) method will be automatically called and the attribute name will be passed to the parameter $property_name. Through this method The internal execution of , returns the value of the private property we passed in. If the member properties are not encapsulated as private, the object
itself will not automatically call this method.
__set() method: This method is used to set values ​​for private member attributes. It has two parameters. The first parameter is the name of the attribute you want to set the value for. The second parameter is the attribute name you want to set the value to. Set value, no return value. This method also does not require us to
call it manually. It can also be made private. It is automatically called when directly setting the private attribute value. The same attribute
private has been encapsulated. If there is no __set () This method is not allowed, for example:
$this->name='zhangsan', this will cause an error, but if you add __set($property_name, $value)
This method will be automatically called when directly assigning a value to a private property. Pass the attribute such as name to
$property_name, and pass the value "zhangsan" to be assigned to $value. Through the execution of this method, To achieve the purpose of assignment
. If the member properties are not encapsulated as private, the object itself will not automatically call this method. In order not to pass in illegal
values, you can also make a judgment in this method. The code is as follows: Code snippet

Copy code The code is as follows:

class Person{
//The following are the member attributes of a person, which are all encapsulated private members
private $name; //The name of the person
private $sex; //The gender of the person
private $age; //The person's Age
//__get() method is used to obtain private properties
private function __get($property_name){
echo "When directly obtaining the private property value, this __get() method is automatically called< ;br>";
if(isset($this->$property_name)) {
return($this->$property_name);
}else {
return(NULL);
}
}
//__set() method is used to set private properties
private function __set($property_name, $value){
echo "When setting private property values ​​directly, This __set() method is automatically called to assign a value to the private property
";
$this->$property_name = $value;
}
}
$p1=new Person( );
//If you directly assign a value to a private attribute, the __set() method will be automatically called to assign the value. "Male";
$p1->age=20;
//Get the value of the private attribute directly, the __get() method will be automatically called to return the value of the member attribute
echo "Name:" .$p1->name."
";
echo "Gender:".$p1->sex."
";
echo "Age:".$p1- >age."
";
?>


Program execution results:
When directly setting the value of a private attribute, the __set() method is automatically called to assign a value to the private attribute. When directly setting the value of a private attribute, the __set() method is automatically called. Assigning values ​​to private attributes
When directly setting the value of a private attribute, the __set() method is automatically called. Assigning a value to a private attribute
When directly obtaining the value of a private attribute, the __get() method is automatically called.
Name: Zhang San
When directly obtaining the private attribute value, this __get() method is automatically called
Gender: Male
When directly obtaining the private attribute value, this is automatically called __get() method
Age: 20
If the above code does not add the __get() and __set() methods, the program will go wrong, because private
members cannot be operated outside the class. The above code helps us directly access the encapsulated private
members by automatically calling the __get() and __set() methods.
__isset() method: Before looking at this method, let’s take a look at the application of the “isset()” function. isset() is a function used to determine whether a variable is set. Pass in a variable as a parameter. If the passed-in variable Returns true if it exists, otherwise returns false.
So if you use the "isset()" function outside an object to determine whether the members in the object are set, can you
use it? There are two situations. If the members in the object are public, we can use this function to determine the member attributes. If they are private member attributes, this function will not work. The reason is that the private ones are encapsulated. , it is not visible from the outside
. Then we can't
use the "isset()" function outside the object to determine whether the private member attribute has been set? Yes, you just need to
add a "__isset()" method to the class. When using the "isset()" function outside the class to determine whether the private members in the object have been set
, the "__isset()" method in the class will be automatically called to help us complete such operations. The "__isset()" method can also be made private. You can just add the following code to the class:
Code snippet

Copy code The code is as follows:

private function __isset($nm){

echo "When the isset() function is used outside the class to determine the private member $nm, it is automatically called
";
return isset($this-> $nm);
}


__unset() method: Before looking at this method, let’s take a look at the “unset()” function first, “unset()”

The function of this function is to delete the specified variable and return true. The parameter is the variable to be deleted. So if you want to delete the member attributes inside the object outside an object
, can you use the "unset()" function? There are two situations. If the member attributes inside a
object are public, you can use it. This function deletes the public attributes of the object outside the object. If the member attributes of the
object are private, I will not have the permission to delete them using this function, but similarly if you add "__unset(( )" method, you can delete the private member attributes of the object outside the object. After adding the "__unset()" method to the object
, when using the "unset()" function outside the object to delete the private
member attributes inside the object, the "__unset()" function will be automatically called to help. We delete the private member attributes inside the object. This method can also be defined as private inside the class. Just add the following code to the object:
Code snippet



Copy code

The code is as follows: private function __unset($nm){

echo "Automatically called when the unset() function is used outside the class to delete a private member
";

unset($this->$nm);
}


Let’s take a look at a complete example:
Code snippet

Copy code

The code is as follows:

class Person{
//The following are the member attributes of the person
private $name; //The person’s name
private $sex; //The person’s Gender
private $age; //Age of a person
//__get() method is used to obtain private properties
private function __get($property_name){
if(isset($this-> $property_name)){
return($this->$property_name);}else {
return(NULL);
}
}
}
//__set() Method used to set private properties
private function __set($property_name, $value){
$this->$property_name = $value;
}
//__isset() method
private function __isset($nm){
echo "When the isset() function determines a private member, it is automatically called
";
return isset($this->$nm);
}
//__unset() method
private function __unset($nm){
echo "Automatically called when the unset() function is used outside the class to delete a private member
";
unset($this->$nm);
}
}
$p1=new Person();
$p1->name="this is a person name";
//When using the isset() function to measure private members, the __isset() method is automatically called to help us complete it, and the return result is true
echo var_dump(isset($p1->name))."echo $p1->name."
";
//When using the unset() function to delete private members, the __unset() method is automatically called to help us complete the task and delete name Private attribute
unset($p1->name);
//has been deleted, so there will be no output in this line
echo $p1->name;
?>

The output result is:
When the isset() function determines a private member, it automatically calls
bool(true)
this is a person name
When unset is used outside the class () function to delete private members. The four methods
__set(), __get(), __isset(), and __unset() are all added to the object and are
automatically called when needed. , to complete the operation of the private properties inside the object outside the object.

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