Theme 类，即一个应用的主题，主要通过替换路径实现主题的应用，里边的方法为获取根路径和根链接，以及应用主题的方法：
namespace yii\base;
use Yii;
use yii\helpers\FileHelper;
/**
* Theme represents an application theme.
* Theme 类，即一个应用的主题
*
* 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[[View::theme|active theme]]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:
* Theme 通过[[pathMap]]来实现视图文件替换：
*
* 1. It first looks for a key in [[pathMap]] that is a substring of the given view file path;
* 首先在[[pathMap]] 中查找关键字，该关键字是一个给定的视图路径的子字符串
* 2. If such a key exists, the corresponding value will be used to replace the corresponding part
* in the view file path;
* 如果该关键字存在，则用对应得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.
* 然后检查替换后的路径对应的文件是否存在，如果存在就替换原来的文件
* 4. If Step 2 or 3 fails, the original view file will be used.
* 如果2和3失败的话，就返回原来的路径
*
* 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,
*
* ```php
* '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.
* 主题的对应关系可以是一个视图文件对应多个主题文件
*
* To use a theme, you should configure the [[View::theme|theme]] property of the "view" application
* component like the following:
*
* ```php
* '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.
*
* @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.
* If this property is empty or not set, a mapping [[Application::basePath]] to [[basePath]] will be used.
* 路径映射属性--用来设置替换映射关系的
*/
public $pathMap;
/**
* @var 设置要访问的资源的url，没有结尾的斜线(without ending slash)
*/
private $_baseUrl;
/**
* @return string the base URL (without ending slash) for this theme. All resources of this theme are considered
* to be under this base URL.
* @return string 返回值为当前主题的基础链接，即访问链接，其他的资源都在该链接下
*/
public function getBaseUrl()
{
return $this->_baseUrl;
}
/**
* @param string $url the base URL or path alias for this theme. All resources of this theme are considered
* to be under this base URL.
* 设置基础访问链接
*/
public function setBaseUrl($url)
{
$this->_baseUrl = rtrim(Yii::getAlias($url), '/');
}
/**
* @var array 当前主题的根路径，该主题的资源都在该目录下
*/
private $_basePath;
/**
* @return string the root path of this theme. All resources of this theme are located under this directory.
* @return string 返回当前主题的根路径，该主题的资源都在该目录下
* @see pathMap
*/
public function getBasePath()
{
return $this->_basePath;
}
/**
* @param string $path the root path or path alias of this theme. All resources of this theme are located
* under this directory.
* 设置当前主题的根路径
* @see pathMap
*/
public function setBasePath($path)
{
$this->_basePath = Yii::getAlias($path);
}
/**
* Converts a file to a themed file if possible.
* 将一个文件替换为允许替换的主题文件---主题的应用原理
* If there is no corresponding themed file, the original file will be returned.
* 如果没有对应的主题文件，将返回源文件
* @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 = $this->pathMap;//取得路径映射[[pathMap]]的值
if (empty($pathMap)) {//如果[[pathMap]]没有设置值，则取当前主题的根路径，否则抛出异常
if (($basePath = $this->getBasePath()) === null) {
throw new InvalidConfigException('The "basePath" property must be set.');
}
$pathMap = [Yii::$app->getBasePath() => [$basePath]];//设置$pathMap的值为[模块根路径=>主题根路径]的形式
}
//对路径中的"/"、“\”进行统一替换
$path = FileHelper::normalizePath($path);
foreach ($pathMap as $from => $tos) {
//映射数组中的来源（旧值）
$from = FileHelper::normalizePath(Yii::getAlias($from)) . DIRECTORY_SEPARATOR;
//如果在$path中有可替换的旧值
if (strpos($path, $from) === 0) {
$n = strlen($from);
//对目标值循环
foreach ((array) $tos as $to) {
$to = FileHelper::normalizePath(Yii::getAlias($to)) . DIRECTORY_SEPARATOR;
//把$path中的$from替换为$to
$file = $to . substr($path, $n);
//如果是文件，直接返回
if (is_file($file)) {
return $file;
}
}
}
}
return $path;
}
/**
* Converts a relative URL into an absolute URL using [[baseUrl]].
* 将一个相对URL替换为绝对URL
* @param string $url the relative URL to be converted.
* @return string the absolute URL
* @throws InvalidConfigException if [[baseUrl]] is not set
*/
public function getUrl($url)
{
if (($baseUrl = $this->getBaseUrl()) !== null) {
return $baseUrl . '/' . ltrim($url, '/');//通过取得[[baseUrl]]的值拼接出当前主题的绝对URL
} else {
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 $path the relative file path to be converted.
* @return string the absolute file path
* @throws InvalidConfigException if [[basePath]] is not set
*/
public function getPath($path)
{
if (($basePath = $this->getBasePath()) !== null) {
return $basePath . DIRECTORY_SEPARATOR . ltrim($path, '/\\');//通过取得[[basePath]]的值拼接出当前主题的绝对路径
} else {
throw new InvalidConfigException('The "basePath" property must be set.');
}
}
}