WordPress标签云小工具详解

WordPress标签云小工具是WordPress程序自带的一个小工具，它可以在我们的博客侧边栏展示网站的标签列表。今天WordPress小工具详解系列就从WordPress标签云小工具开始。带大家熟悉标签云小工具的各个细节。

在【外观->小工具】菜单中就可以找到标签云小工具，将它拖到我们的侧边栏中，就可以了。

我们可以设置标签云小工具的标题，你可以取你想要展示的名称【如：热门标签，热门搜索，标签云集等等】。还能设置标签的分类法，WordPress标签小工具可以设置标签分类法和链接分类目录。如下图：

设置完成，保存就可以了。

这是WordPress头条的标签云小工具。CSS文件在文章末尾贴给大家。
下面我们来深入分析标签云小工具的源码实现：
标签云源码位置：wp-includes\widgets\class-wp-widget-tag-cloud.php
源代码：(since 4.4.0)

 __( 'A cloud of your most used tags.' ),
			'customize_selective_refresh' => true,
		);
		parent::__construct( 'tag_cloud', __( 'Tag Cloud' ), $widget_ops );
	}

	/**
	 * Outputs the content for the current Tag Cloud widget instance.
	 *
	 * @since 2.8.0
	 * @access public
	 *
	 * @param array $args     Display arguments including 'before_title', 'after_title',
	 *                        'before_widget', and 'after_widget'.
	 * @param array $instance Settings for the current Tag Cloud widget instance.
	 */
	public function widget( $args, $instance ) {
		$current_taxonomy = $this->_get_current_taxonomy($instance);
		if ( !empty($instance['title']) ) {
			$title = $instance['title'];
		} else {
			if ( 'post_tag' == $current_taxonomy ) {
				$title = __('Tags');
			} else {
				$tax = get_taxonomy($current_taxonomy);
				$title = $tax->labels->name;
			}
		}

		/**
		 * Filter the taxonomy used in the Tag Cloud widget.
		 *
		 * @since 2.8.0
		 * @since 3.0.0 Added taxonomy drop-down.
		 *
		 * @see wp_tag_cloud()
		 *
		 * @param array $current_taxonomy The taxonomy to use in the tag cloud. Default 'tags'.
		 */
		$tag_cloud = wp_tag_cloud( apply_filters( 'widget_tag_cloud_args', array(
			'taxonomy' => $current_taxonomy,
			'echo' => false
		) ) );

		if ( empty( $tag_cloud ) ) {
			return;
		}

		/** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
		$title = apply_filters( 'widget_title', $title, $instance, $this->id_base );

		echo $args['before_widget'];
		if ( $title ) {
			echo $args['before_title'] . $title . $args['after_title'];
		}

		echo '
';

		echo $tag_cloud;

		echo "
\n";
		echo $args['after_widget'];
	}

	/**
	 * Handles updating settings for the current Tag Cloud widget instance.
	 *
	 * @since 2.8.0
	 * @access public
	 *
	 * @param array $new_instance New settings for this instance as input by the user via
	 *                            WP_Widget::form().
	 * @param array $old_instance Old settings for this instance.
	 * @return array Settings to save or bool false to cancel saving.
	 */
	public function update( $new_instance, $old_instance ) {
		$instance = array();
		$instance['title'] = sanitize_text_field( $new_instance['title'] );
		$instance['taxonomy'] = stripslashes($new_instance['taxonomy']);
		return $instance;
	}

	/**
	 * Outputs the Tag Cloud widget settings form.
	 *
	 * @since 2.8.0
	 * @access public
	 *
	 * @param array $instance Current settings.
	 */
	public function form( $instance ) {
		$current_taxonomy = $this->_get_current_taxonomy($instance);
		$title_id = $this->get_field_id( 'title' );
		$instance['title'] = ! empty( $instance['title'] ) ? esc_attr( $instance['title'] ) : '';

		echo '
' . __( 'Title:' ) . '
			
		
';

		$taxonomies = get_taxonomies( array( 'show_tagcloud' => true ), 'object' );
		$id = $this->get_field_id( 'taxonomy' );
		$name = $this->get_field_name( 'taxonomy' );
		$input = '';

		switch ( count( $taxonomies ) ) {

		// No tag cloud supporting taxonomies found, display error message
		case 0:
			echo '
' . __( 'The tag cloud will not be displayed since there are no taxonomies that support the tag cloud widget.' ) . '
';
			printf( $input, '' );
			break;

		// Just a single tag cloud supporting taxonomy found, no need to display options
		case 1:
			$keys = array_keys( $taxonomies );
			$taxonomy = reset( $keys );
			printf( $input, esc_attr( $taxonomy ) );
			break;

		// More than one tag cloud supporting taxonomy found, display options
		default:
			printf(
				'
%2$s' .
				'',
				$id,
				__( 'Taxonomy:' ),
				$name
			);

			foreach ( $taxonomies as $taxonomy => $tax ) {
				printf(
					'%s',
					esc_attr( $taxonomy ),
					selected( $taxonomy, $current_taxonomy, false ),
					$tax->labels->name
				);
			}

			echo '
';
		}
	}

	/**
	 * Retrieves the taxonomy for the current Tag cloud widget instance.
	 *
	 * @since 4.4.0
	 * @access public
	 *
	 * @param array $instance Current settings.
	 * @return string Name of the current taxonomy if set, otherwise 'post_tag'.
	 */
	public function _get_current_taxonomy($instance) {
		if ( !empty($instance['taxonomy']) && taxonomy_exists($instance['taxonomy']) )
			return $instance['taxonomy'];

		return 'post_tag';
	}
}

这里我们主要看一下这几行代码：

$tag_cloud = wp_tag_cloud( apply_filters( 'widget_tag_cloud_args', array(
			'taxonomy' => $current_taxonomy,
			'echo' => false
		) ) );

主要知识点wp_tag_cloud函数和apply_filters函数。我们知道apply_filters是一个函数过滤器。这样我们就可以定制wp_tag_cloud函数的参数了。
具体的修改方法，请查看如何修改WordPress标签云小工具,你还可以根据WordPress标签云小工具的源码开发属于自己的标签云小工具。
附（本网站使用的标签云小工具CSS代码）：

        /* tag-cloud widget */
	.widget_links {}
	.widget_links li:after {}
	.widget_links li:before {}
	.widget_tag_cloud {}
	.widget_tag_cloud a { padding:3px; float: left;
		margin: 0 10px 10px 0;
		padding: 0 15px;
		background: #fff;
		color: #5e6b73;
		font-size: 14px;
		height: 30px;
		line-height: 30px;
		border: 1px solid #E8ECEF;
		border-radius: 16px;
		-webkit-border-radius: 16px; }
	.widget_tag_cloud a:hover{background: #a0aebc;border-color: #a0aebc;color: #fff;}
	.widget_tag_cloud a:after {}
	.widget_tag_cloud a:before {}
	.tagcloud { padding:15px 0 15px 0; }

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