/**
      * Returns an ID that uniquely identifies this module among all modules within the current application.
      * 返回模块的唯一标识
      * Note that if the module is an application, an empty string will be returned.
      * @return string the unique ID of the module.
      */
     public function getUniqueId()
     {
         //三元运算符，如果当前模块有父模块，则返回[父模块ID/当前模块ID]的格式作为唯一ID，否则只返回当前模块ID
         return $this->module ? ltrim($this->module->getUniqueId() . '/' . $this->id, '/') : $this->id;
     }

     /**
      * Returns the root directory of the module.
      * 返回当前模块的根路径
      * It defaults to the directory containing the module class file.
      * @return string the root directory of the module.
      */
     public function getBasePath()
     {
         if ($this->_basePath === null) {
             $class = new \ReflectionClass($this);//生成当前类的反射对象
             $this->_basePath = dirname($class->getFileName());//getFileName()取得类定义的路径
         }

         return $this->_basePath;
     }

     /**
      * Sets the root directory of the module.
      * 设置当前模块的根路径
      * This method can only be invoked at the beginning of the constructor.
      * @param string $path the root directory of the module. This can be either a directory name or a path alias.
      * @throws InvalidParamException if the directory does not exist.
      */
     public function setBasePath($path)
     {
         $path = Yii::getAlias($path);
         $p = realpath($path);
         if ($p !== false && is_dir($p)) {
             $this->_basePath = $p;
         } else {
             throw new InvalidParamException("The directory does not exist: $path");
         }
     }

     /**
      * Returns the directory that contains the controller classes according to [[controllerNamespace]].
      * 根据控制器的命名空间返回控制器的目录路径
      * Note that in order for this method to return a value, you must define
      * an alias for the root namespace of [[controllerNamespace]].
      * 为了使该方法返回正确的值，必须为[[controllerNamespace]]定义一个根别名
      * @return string the directory that contains the controller classes.
      * @throws InvalidParamException if there is no alias defined for the root namespace of [[controllerNamespace]].
      */
     public function getControllerPath()
     {
         //通过将命名空间转换为路径构造别名路径，然后通过getAlias方法取得控制器的绝对路径
         return Yii::getAlias('@' . str_replace('\\', '/', $this->controllerNamespace));
     }

     /**
      * Returns the directory that contains the view files for this module.
      * 取得当前模块的视图文件目录路径
      * @return string the root directory of view files. Defaults to "[[basePath]]/views".
      */
     public function getViewPath()
     {
         if ($this->_viewPath === null) {
             $this->_viewPath = $this->getBasePath() . DIRECTORY_SEPARATOR . 'views';//getBasePath()返回当前模块的根路径，然后拼接出视图文件路径
         }
         return $this->_viewPath;
     }

     /**
      * Sets the directory that contains the view files.
      * 设置视图文件目录路径
      * @param string $path the root directory of view files.
      * @throws InvalidParamException if the directory is invalid
      */
     public function setViewPath($path)
     {
         $this->_viewPath = Yii::getAlias($path);
     }

     /**
      * Returns the directory that contains layout view files for this module.
      * 取得当前模块的布局文件路径
      * @return string the root directory of layout files. Defaults to "[[viewPath]]/layouts".
      */
     public function getLayoutPath()
     {
         if ($this->_layoutPath === null) {
             $this->_layoutPath = $this->getViewPath() . DIRECTORY_SEPARATOR . 'layouts';//getBasePath()返回当前模块的根路径，然后拼接出布局文件目录路径
         }

         return $this->_layoutPath;
     }

     /**
      * Sets the directory that contains the layout files.
      * 设置当前模块的布局文件路径
      * @param string $path the root directory or path alias of layout files.
      * @throws InvalidParamException if the directory is invalid
      */
     public function setLayoutPath($path)
     {
         $this->_layoutPath = Yii::getAlias($path);
     }

     /**
      * Defines path aliases.
      * 定义路径别名
      * This method calls [[Yii::setAlias()]] to register the path aliases.
      * This method is provided so that you can define path aliases when configuring a module.
      * 通过调用[[Yii::setAlias()]]注册路径别名，方便在配置模块的时候定义路径别名
      * @property array list of path aliases to be defined. The array keys are alias names
      * (must start with '@') and the array values are the corresponding paths or aliases.
      * See [[setAliases()]] for an example.
      * @param array $aliases list of path aliases to be defined. The array keys are alias names
      * (must start with '@') and the array values are the corresponding paths or aliases.
      * For example,
      * 传入测参数的格式，键名为别名名称，以@开始，键值为对应的路径
      * ```php
      * [
      *     '@models' => '@app/models', // an existing alias
      *     '@backend' => __DIR__ . '/../backend',  // a directory
      * ]
      * ```
      */
     public function setAliases($aliases)
     {
         foreach ($aliases as $name => $alias) {
             Yii::setAlias($name, $alias);//调用[[Yii::setAlias()]]注册路径别名
         }
     }

     /**
      * Checks whether the child module of the specified ID exists.
      * This method supports checking the existence of both child and grand child modules.
      * @param string $id module ID. For grand child modules, use ID path relative to this module (e.g. `admin/content`).
      * @return boolean whether the named module exists. Both loaded and unloaded modules
      * are considered.
      */
     public function hasModule($id)
     {
         if (($pos = strpos($id, '/')) !== false) {//如果模块ID格式为 `admin/content`
             // sub-module
             $module = $this->getModule(substr($id, 0, $pos));//取出当前模块的子模块

             return $module === null ? false : $module->hasModule(substr($id, $pos + 1));//如果没有取到，返回false，否则判断子模块的子模块
         } else {//模块ID没有父模块的情况，直接判断_modules数组中是否有值
             return isset($this->_modules[$id]);
         }
     }