Detailed explanation of related PHP functions for creating and adding filters in WordPress, wordpress filter_PHP tutorial

Detailed explanation of related PHP functions to create and add filters in WordPress, wordpress filters

apply_filters() (create filters)
The apply_filters() function is used to create a filter, most of which are used in functions. It is a very important function in the WordPress plug-in mechanism, allowing other themes and plug-ins to modify and filter a value.

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 it, the value of $value will be returned directly.

Example

No one filters:

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

Print results:

Values ​​that can be modified

Someone filtered:

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

Print results:

Modify 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 filter to mount (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, please refer to the PHP callback function type documentation.

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) 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:

test parameter 2 parameter 3

Others

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

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