组件配置添加：

'request' => [

            'parsers' => [

                'application/json' => 'yii\web\JsonParser',

                'application/xml' => 'common\components\XmlParser',

                'text/xml' => 'common\components\XmlParser'

            ]

        ],

        'response' => [

            'formatters' => [

                \yii\web\Response::FORMAT_XML => [

                    'class' => 'yii\web\XmlResponseFormatter',

                    'rootTag' => 'xml'

                ]

            ]

        ]

common\components\XmlParser

<?php

namespace common\components;

use yii\base\InvalidParamException;

use yii\web\BadRequestHttpException;

use yii\web\RequestParserInterface;

class XmlParser implements RequestParserInterface

{

    public $asArray = true;

    public $throwException = true;

    /**

     * Parses a HTTP request body.

     * @param string $rawBody the raw HTTP request body.

     * @param string $contentType the content type specified for the request body.

     * @return array parameters parsed from the request body

     * @throws BadRequestHttpException if the body contains invalid json and [[throwException]] is `true`.

     */

    public function parse($rawBody, $contentType)

    {

        try {

            $parameters = simplexml_load_string($rawBody, 'SimpleXMLElement', LIBXML_NOCDATA);

            $parameters = $this->asArray ? (array) $parameters : $parameters;

            return $parameters === null ? [] : $parameters;

        } catch (InvalidParamException $e) {

            if ($this->throwException) {

                throw new BadRequestHttpException('Invalid XML data in request body: ' . $e->getMessage());

            }

            return [];

        }

    }

}

然后就可以在控制器里直接取$params = Yii::$app->bodyParams

xml格式适合微信公众号开发。