Detailed explanation of related PHP functions for creating and adding filters in WordPress

apply_filters() (create filter)
apply_filters() function is used to create a filter. Most of them are used in functions. It is a very important function in the WordPress plug-in mechanism, allowing other themes and plug-ins to match a value. Perform modification filtering.

Usage

apply_filters( $tag, $value, $var... );

Parameters

$tag

(String) (required) The name of the filter.

Default value: None

$value

(Mixed) (Required) The value to be filtered. If no one filters, this value will be returned directly.

$var

(Mixed) (Optional) Pass additional variable parameters to the filter function to assist the filter function in operating the return value. Unlimited numbers can be added.

Return value

(mixed) filtered value. If no one filters, the value of $value will be returned directly.

Example

No one is filtering:

echo apply_filters( 'test', '可以被修改的值' );

Print result:

The value that can be modified

Someone is filtering:

function test_func(){
  return '修改值';
}
add_filter( 'test', 'test_func' );
echo apply_filters( 'test', '可以被修改的值' );

Print result:

Modified value

Receive parameters:

function test_func(){
  return '修改值';
}
add_filter( 'test', 'test_func' );
function test_func2( $text ){
  return $text . '2';
}
add_filter( 'test', 'test_func2' );
echo apply_filters( 'test', '可以被修改的值' );

Multiple parameters:

function test_func( $text, $var, $var2 ){
  return '修改值' . $var1 . $var2;
}
add_action( 'test', 'test_func', 10, 3 );
echo apply_filters( 'test', '可以被修改的值', '辅助值1', '辅助值2' );

Others

This function is located at: wp-includes/plugin.php

add_filter() (add filter)
add_filter() can mount a function to the specified filter.

Usage

add_filter( $tag, $function_to_add, $priority, $accepted_args );

Parameters

$tag

(string) (required) The name of the mounted filter (same as the $tag attribute of the target apply_filters() function).

Default value: None

$function_to_add

(callback) (required) The callback function to be mounted, refer to the PHP callback function type document.

Default value: None

$priority

(integer) (optional) Execution order, the smaller the function, the first it will be executed.

Default value: 10

$accepted_args

(integer) (optional) The number of parameters received by the callback function. Setting multiple parameters can receive more parameters passed in by the apply_filters() function.

Default value: 1

Return value

(boolean) is always True

Example

function test_func( $text, $var1, $var2 ){
  return $text . $var1 . $var2;
}
add_action( 'test', 'test_func', 10, 3 );
echo apply_filters( 'test', '参数2', '参数3', '参数4' );

Print:

testparameter2parameter3

other

This function is located in: wp-includes/plugin. php

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