描述：
为博客后台管理界面添加一个Meta模块
用法：
<?php add_meta_box( $id, $title, $callback, $screen, $context,$priority, $callback_args );?>参数：
$id
(string) (必填) Meta模块的 HTML“ID”属性
默认值: None
$title
(string) (必填) Meta模块的标题，对用户可见
默认值: None
$callback
(callback) (必填) 为Meta模块输出 HTML代码的函数
默认值: None
$screen
(string) (可选) 显示编辑屏幕部分的书写屏幕类型（示例包括’post’、’page’、’dashboard’、’link’、’attachment’、’custom_post_type’、’comment’，其中custom_post_type是custom post type slug）
默认值: null
$context
(string) (可选) 页面上显示编辑屏幕部分的部分（“普通”、“高级”或“侧边”）。（注意2.7之前不存在“侧”）
默认值: ‘advanced’
$priority
(string) (可选) 上下文中框应显示的优先级（’high’、’core’、’default’或’low’）
默认值: ‘default’
$callback_args
(array) (可选) 要传递到回调函数的参数。回调将接收$post对象以及通过该变量传递的任何参数。
默认值: null
示例：
<?php
/**
* Adds a box to the main column on the Post and Page edit screens.
*/
function myplugin_add_meta_box() {
$screens = array( 'post', 'page' );
foreach ( $screens as $screen ) {
add_meta_box(
'myplugin_sectionid',
__( 'My Post Section Title', 'myplugin_textdomain' ),
'myplugin_meta_box_callback',
$screen
);
}
}
add_action( 'add_meta_boxes', 'myplugin_add_meta_box' );
/**
* Prints the box content.
*
* @param WP_Post $post The object for the current post/page.
*/
function myplugin_meta_box_callback( $post ) {
// Add a nonce field so we can check for it later.
wp_nonce_field( 'myplugin_save_meta_box_data', 'myplugin_meta_box_nonce' );
/*
* Use get_post_meta() to retrieve an existing value
* from the database and use the value for the form.
*/
$value = get_post_meta( $post->ID, '_my_meta_value_key', true );
echo '<label for="myplugin_new_field">';
_e( 'Description for this field', 'myplugin_textdomain' );
echo '</label> ';
echo '<input type="text" id="myplugin_new_field" name="myplugin_new_field" value="' . esc_attr( $value ) . '" size="25" />';
}
/**
* When the post is saved, saves our custom data.
*
* @param int $post_id The ID of the post being saved.
*/
function myplugin_save_meta_box_data( $post_id ) {
/*
* We need to verify this came from our screen and with proper authorization,
* because the save_post action can be triggered at other times.
*/
// Check if our nonce is set.
if ( ! isset( $_POST['myplugin_meta_box_nonce'] ) ) {
return;
}
// Verify that the nonce is valid.
if ( ! wp_verify_nonce( $_POST['myplugin_meta_box_nonce'], 'myplugin_save_meta_box_data' ) ) {
return;
}
// If this is an autosave, our form has not been submitted, so we don't want to do anything.
if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
return;
}
// Check the user's permissions.
if ( isset( $_POST['post_type'] ) && 'page' == $_POST['post_type'] ) {
if ( ! current_user_can( 'edit_page', $post_id ) ) {
return;
}
} else {
if ( ! current_user_can( 'edit_post', $post_id ) ) {
return;
}
}
/* OK, it's safe for us to save the data now. */
// Make sure that it is set.
if ( ! isset( $_POST['myplugin_new_field'] ) ) {
return;
}
// Sanitize user input.
$my_data = sanitize_text_field( $_POST['myplugin_new_field'] );
// Update the meta field in the database.
update_post_meta( $post_id, '_my_meta_value_key', $my_data );
}
add_action( 'save_post', 'myplugin_save_meta_box_data' );源文件：
/**
* Add a meta box to an edit form.
*
* @since 2.5.0
*
* @global array $wp_meta_boxes
*
* @param string $id String for use in the 'id' attribute of tags.
* @param string $title Title of the meta box.
* @param callback $callback Function that fills the box with the desired content.
* The function should echo its output.
* @param string|WP_Screen $screen Optional. The screen on which to show the box (like a post
* type, 'link', or 'comment'). Default is the current screen.
* @param string $context Optional. The context within the screen where the boxes
* should display. Available contexts vary from screen to
* screen. Post edit screen contexts include 'normal', 'side',
* and 'advanced'. Comments screen contexts include 'normal'
* and 'side'. Menus meta boxes (accordion sections) all use
* the 'side' context. Global default is 'advanced'.
* @param string $priority Optional. The priority within the context where the boxes
* should show ('high', 'low'). Default 'default'.
* @param array $callback_args Optional. Data that should be set as the $args property
* of the box array (which is the second parameter passed
* to your callback). Default null.
*/
function add_meta_box( $id, $title, $callback, $screen = null, $context = 'advanced', $priority = 'default', $callback_args = null ) {
global $wp_meta_boxes;
if ( empty( $screen ) )
$screen = get_current_screen();
elseif ( is_string( $screen ) )
$screen = convert_to_screen( $screen );
$page = $screen->id;
if ( !isset($wp_meta_boxes) )
$wp_meta_boxes = array();
if ( !isset($wp_meta_boxes[$page]) )
$wp_meta_boxes[$page] = array();
if ( !isset($wp_meta_boxes[$page][$context]) )
$wp_meta_boxes[$page][$context] = array();
foreach ( array_keys($wp_meta_boxes[$page]) as $a_context ) {
foreach ( array('high', 'core', 'default', 'low') as $a_priority ) {
if ( !isset($wp_meta_boxes[$page][$a_context][$a_priority][$id]) )
continue;
// If a core box was previously added or removed by a plugin, don't add.
if ( 'core' == $priority ) {
// If core box previously deleted, don't add
if ( false === $wp_meta_boxes[$page][$a_context][$a_priority][$id] )
return;
/*
* If box was added with default priority, give it core priority to
* maintain sort order.
*/
if ( 'default' == $a_priority ) {
$wp_meta_boxes[$page][$a_context]['core'][$id] = $wp_meta_boxes[$page][$a_context]['default'][$id];
unset($wp_meta_boxes[$page][$a_context]['default'][$id]);
}
return;
}
// If no priority given and id already present, use existing priority.
if ( empty($priority) ) {
$priority = $a_priority;
/*
* Else, if we're adding to the sorted priority, we don't know the title
* or callback. Grab them from the previously added context/priority.
*/
} elseif ( 'sorted' == $priority ) {
$title = $wp_meta_boxes[$page][$a_context][$a_priority][$id]['title'];
$callback = $wp_meta_boxes[$page][$a_context][$a_priority][$id]['callback'];
$callback_args = $wp_meta_boxes[$page][$a_context][$a_priority][$id]['args'];
}
// An id can be in only one priority and one context.
if ( $priority != $a_priority || $context != $a_context )
unset($wp_meta_boxes[$page][$a_context][$a_priority][$id]);
}
}
if ( empty($priority) )
$priority = 'low';
if ( !isset($wp_meta_boxes[$page][$context][$priority]) )
$wp_meta_boxes[$page][$context][$priority] = array();
$wp_meta_boxes[$page][$context][$priority][$id] = array('id' => $id, 'title' => $title, 'callback' => $callback, 'args' => $callback_args);
}
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