yii2源码学习笔记(十七）

Theme 类，应用的主题，通过替换路径实现主题的应用，方法为获取根路径和根链接：yii2\base\Theme.php

<?php
/**
 * @link http://www.yiiframework.com/
 * @copyright Copyright (c) 2008 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

namespace yii\base;

use Yii;
use yii\helpers\FileHelper;

/**
 * Theme represents an application theme.
 * Theme 类，应用的主题
 * When [[View]] renders a view file, it will check the [[View::theme|active theme]]
 * to see if there is a themed version of the view file exists. If so, the themed version will be rendered instead.
 * 视图对象[[View]]渲染视图文件的时候，会检查视图的主题是否存在，如果存在则渲染主题取代默认样式
 * A theme is a directory consisting of view files which are meant to replace their non-themed counterparts.
 *
 * Theme uses [[pathMap]] to achieve the view file replacement:
 *
 * 1. It first looks for a key in [[pathMap]] that is a substring of the given view file path;
 *  首先查找关键字，关键字是一个给定的视图路径的字符串
 * 2. If such a key exists, the corresponding value will be used to replace the corresponding part
 *    in the view file path;关键字存在，则用对应值替换给定的视图文件路径中对应的部分
 * 3. It will then check if the updated view file exists or not. If so, that file will be used
 *    to replace the original view file.检查替换后的路径对应的文件是否存在，存在就替换原文件
 * 4. If Step 2 or 3 fails, the original view file will be used.
 * 2和3失败的话，返回原来的路径
 * For example, if [[pathMap]] is `['@app/views' => '@app/themes/basic']`,
 * then the themed version for a view file `@app/views/site/index.php` will be
 * `@app/themes/basic/site/index.php`.
 *
 * It is possible to map a single path to multiple paths. For example,
 *
 * ~~~
 * 'pathMap' => [
 *     '@app/views' => [
 *         '@app/themes/christmas',
 *         '@app/themes/basic',
 *     ],
 * ]
 * ~~~
 *
 * In this case, the themed version could be either `@app/themes/christmas/site/index.php` or
 * `@app/themes/basic/site/index.php`. The former has precedence over the latter if both files exist.
 *
 * To use a theme, you should configure the [[View::theme|theme]] property of the "view" application
 * component like the following:
 *
 * ~~~
 * 'view' => [
 *     'theme' => [
 *         'basePath' => '@app/themes/basic',
 *         'baseUrl' => '@web/themes/basic',
 *     ],
 * ],
 * ~~~
 *
 * The above configuration specifies a theme located under the "themes/basic" directory of the Web folder
 * that contains the entry script of the application. If your theme is designed to handle modules,
 * you may configure the [[pathMap]] property like described above.
 *
 * @property string $basePath The root path of this theme. All resources of this theme are located under this
 * directory.
 * @property string $baseUrl The base URL (without ending slash) for this theme. All resources of this theme
 * are considered to be under this base URL. This property is read-only.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class Theme extends Component
{
    /**
     * @var array the mapping between view directories and their corresponding themed versions.
     * This property is used by [[applyTo()]] when a view is trying to apply the theme.
     * Path aliases can be used when specifying directories.
     * 路径映射属性 设置替换映射关系
     * If this property is empty or not set, a mapping [[Application::basePath]] to [[basePath]] will be used.
     */
    public $pathMap;

    private $_baseUrl;//设置要访问资源的url

    /**
     * @return string the base URL (without ending slash) for this theme. All resources of this theme are considered
     * to be under this base URL. 返回当前主题的基础链接，其他资源都在链接里
     */
    public function getBaseUrl()
    {
        return $this->_baseUrl;
    }

    /**
     * @param $url string the base URL or path alias for this theme. All resources of this theme are considered
     * to be under this base URL. 设置基础链接
     */
    public function setBaseUrl($url)
    {
        $this->_baseUrl = rtrim(Yii::getAlias($url), '/');
    }

    private $_basePath;//根路径

    /**
     * @return string the root path of this theme. All resources of this theme are located under this directory.
     * 得到当前主题的根路径
     * @see pathMap
     */
    public function getBasePath()
    {
        return $this->_basePath;
    }

    /**
     * @param string $path the root path or path alias of this theme. All resources of this theme are located
     * under this directory. 设置当前主题根路径
     * @see pathMap
     */
    public function setBasePath($path)
    {
        $this->_basePath = Yii::getAlias($path);
    }

    /**
     * Converts a file to a themed file if possible. 将一个文件替换主题文件
     * If there is no corresponding themed file, the original file will be returned.
     * 没有相应的主题文件，返回原文件。
     * @param string $path the file to be themed
     * @return string the themed file, or the original file if the themed version is not available.
     * @throws InvalidConfigException if [[basePath]] is not set
     */
    public function applyTo($path)
    {
        $pathMap = $this->pathMap; //取得路径映射
        if (empty($pathMap)) {//没有设置值 抛出异常
            if (($basePath = $this->getBasePath()) === null) {
                throw new InvalidConfigException('The "basePath" property must be set.');
            }
            //设置值为[模块根路径=>主题根路径]的形式
            $pathMap = [Yii::$app->getBasePath() => [$basePath]];
        }

        $path = FileHelper::normalizePath($path);//对路径中的"/"."\"进行统一

        foreach ($pathMap as $from => $tos) {
            //映射数组中的来源
            $from = FileHelper::normalizePath(Yii::getAlias($from)) . DIRECTORY_SEPARATOR;
            if (strpos($path, $from) === 0) {//如果在$path中有可替换的旧值
                $n = strlen($from);
                foreach ((array) $tos as $to) {
                    $to = FileHelper::normalizePath(Yii::getAlias($to)) . DIRECTORY_SEPARATOR;
                    $file = $to . substr($path, $n);//把$path中的$from替换为$to
                    if (is_file($file)) {
                        return $file; //是文件直接返回
                    }
                }
            }
        }

        return $path;
    }

    /**
     * Converts a relative URL into an absolute URL using [[baseUrl]].
     * 将一个相对URL转换为绝对URL
     * @param string $url the relative URL to be converted.要转换的相对URL
     * @return string the absolute URL  替换后的绝对URL
     * @throws InvalidConfigException if [[baseUrl]] is not set
     */
    public function getUrl($url)
    {
        if (($baseUrl = $this->getBaseUrl()) !== null) {//URL存在，进行转换
            return $baseUrl . '/' . ltrim($url, '/');
        } else {//不存在抛出异常
            throw new InvalidConfigException('The "baseUrl" property must be set.');
        }
    }

    /**
     * Converts a relative file path into an absolute one using [[basePath]].
     * 通过相对路径生成绝对路径
     * @param string $path the relative file path to be converted. 要转换的相对文件路径。
     * @return string the absolute file path 转换后的绝对路径
     * @throws InvalidConfigException if [[baseUrl]] is not set
     */
    public function getPath($path)
    {
        if (($basePath = $this->getBasePath()) !== null) {
            //返回拼接的路径
            return $basePath . DIRECTORY_SEPARATOR . ltrim($path, '/\\');
        } else {
            throw new InvalidConfigException('The "basePath" property must be set.');
        }
    }
}