has_filter()
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概述
has_filter() 函数用于检查指定的过滤器钩子是否已注册任何回调函数。它支持检查钩子是否有任何注册，或特定回调函数是否已附加，并可指定优先级进行验证。
关键要点
- 函数签名：has_filter( $hook_name, $callback = false, $priority = false )，返回 bool 或 int 类型值。
- 当省略 $callback 时，返回布尔值表示钩子是否有任何注册；提供 $callback 时，返回该回调的优先级或 false（如果未附加）。
- 如果同时提供 $callback 和 $priority，返回布尔值表示特定回调是否在指定优先级注册。
- 注意：使用 $callback 参数时，返回值可能为非布尔假值（如 0），建议用 === 运算符测试返回值。
- 相关函数：has_action() 用于检查动作钩子。
代码示例
// 检查钩子是否有任何注册
if ( has_filter( 'the_content' ) ) {
// 执行操作
}
// 检查特定回调是否注册
$priority = has_filter( 'the_content', 'my_callback_function' );
if ( $priority !== false ) {
echo "回调已注册，优先级为：$priority";
}
// 检查回调是否在特定优先级注册
if ( has_filter( 'the_content', 'my_callback_function', 10 ) ) {
// 回调在优先级 10 注册
}注意事项
在性能方面，直接调用 add_filter() 可能比先用 has_filter() 检查再添加更快；has_filter() 更适合检查钩子是否有任何注册，而非避免重复注册特定回调。
原文内容
Checks if any filter has been registered for a hook.
Description
When using the $callback argument, this function may return a non-boolean value that evaluates to false (e.g. 0), so use the === operator for testing the return value.
Parameters
$hook_namestringrequired-
The name of the filter hook.
$callbackcallable|string|array|falseoptional-
The callback to check for.
This function can be called unconditionally to speculatively check a callback that may or may not exist.Default:
false $priorityint|falseoptional-
The specific priority at which to check for the callback.
Default:
false
Source
function has_filter( $hook_name, $callback = false, $priority = false ) {
global $wp_filter;
if ( ! isset( $wp_filter[ $hook_name ] ) ) {
return false;
}
return $wp_filter[ $hook_name ]->has_filter( $hook_name, $callback, $priority );
}
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Codex
Basic Example
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Lance Cleveland
add_filter() calls the same _wp_filter_build_unique_id() function and re-assigns the method/function parameter to the index array.
It is very likely that calling add_filter() with the same parameter list is faster than first checking if the method/function is already registered with has_filter( , ) before adding it with add_filter( , );
I am guessing the best use-case for has_filter() is to check if a filter has ANY registered methods versus checking that a specific method exists prior to re-registering it with add_filter() .