View继承了component，用于渲染视图文件：yii2\base\View.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;
use yii\widgets\Block;
use yii\widgets\ContentDecorator;
use yii\widgets\FragmentCache; /**
* View represents a view object in the MVC pattern.
* MVC中的视图
* View provides a set of methods (e.g. [[render()]]) for rendering purpose.
* 视图提供了一套渲染页面的方法
* @property string|boolean $viewFile The view file currently being rendered. False if no view file is being
* rendered. This property is read-only.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @since 2.0
*/
class View extends Component
{
/**
* @event Event an event that is triggered by [[beginPage()]].
* 事件被[beginPage()]触发
*/
const EVENT_BEGIN_PAGE = 'beginPage';
/**
* @event Event an event that is triggered by [[endPage()]].
* 事件被[endPage()]触发
*/
const EVENT_END_PAGE = 'endPage';
/**
* @event ViewEvent an event that is triggered by [[renderFile()]] right before it renders a view file.
* 事件被[renderFile()]触发前呈现一个视图文件
*/
const EVENT_BEFORE_RENDER = 'beforeRender';
/**
* @event ViewEvent an event that is triggered by [[renderFile()]] right after it renders a view file.
* 事件被[renderFile()]触发后呈现一个视图文件
*/
const EVENT_AFTER_RENDER = 'afterRender'; /**
* @var ViewContextInterface the context under which the [[renderFile()]] method is being invoked.
* ViewContextInterface背景下 [renderFile()]方法被调用
*/
public $context;
/**
* @var mixed custom parameters that are shared among view templates.
* 视图模板*享的自定义参数
*/
public $params = [];
/**
* @var array a list of available renderers indexed by their corresponding supported file extensions.
* Each renderer may be a view renderer object or the configuration for creating the renderer object.
* 一个可用的渲染索引列表。每个渲染器是一个渲染器对象或创建渲染对象配置数组
* For example, the following configuration enables both Smarty and Twig view renderers:
*
* ~~~
* [
* 'tpl' => ['class' => 'yii\smarty\ViewRenderer'],
* 'twig' => ['class' => 'yii\twig\ViewRenderer'],
* ]
* ~~~
*
* If no renderer is available for the given view file, the view file will be treated as a normal PHP
* and rendered via [[renderPhpFile()]].
*/
public $renderers;
/**
* @var string the default view file extension. This will be appended to view file names if they don't have file extensions.
* 默认视图文件扩展名，文件没有扩展名的情况下自动加载
*/
public $defaultExtension = 'php';
/**
* @var Theme|array|string the theme object or the configuration for creating the theme object.
* If not set, it means theming is not enabled.主题对象或创建主题对象的配置 未设置则不启用
*/
public $theme;
/**
* @var array a list of named output blocks. The keys are the block names and the values
* are the corresponding block content. You can call [[beginBlock()]] and [[endBlock()]]
* to capture small fragments of a view. They can be later accessed somewhere else
* through this property.
* 一个输出块列表。键是块名称值为内容。可以调用 [beginblock()]和[endblock()]捕获视图的小片段
* 可以在其他地方通过这个属性访问。
*/
public $blocks;
/**
* @var array a list of currently active fragment cache widgets. This property
* is used internally to implement the content caching feature. Do not modify it directly.
* 当前操作片段的缓存部件列表。用于内部实现内容缓存功能。不要直接修改
* @internal
*/
public $cacheStack = [];
/**
* @var array a list of placeholders for embedding dynamic contents. This property
* is used internally to implement the content caching feature. Do not modify it directly.
* 嵌入动态内容占位符列表。 用于内部实现内容缓存功能。不要直接修改
* @internal
*/
public $dynamicPlaceholders = []; /**
* @var array the view files currently being rendered. There may be multiple view files being
* rendered at a moment because one view may be rendered within another.
* 正在渲染的视图文件。可能有多个视图文件被渲染，因为一个视图可以在另一个视图中呈现
*/
private $_viewFiles = []; /**
* Initializes the view component.初始化视图组件
*/
public function init()
{
parent::init(); //调用父类的方法
if (is_array($this->theme)) {
if (!isset($this->theme['class'])) {
$this->theme['class'] = 'yii\base\Theme';//是数组，没有设置类名，则类名'yii\base\Theme'
}
$this->theme = Yii::createObject($this->theme);//设置了类名，调用配置创建对象
} elseif (is_string($this->theme)) {//以字符串参数的形式创建对象
$this->theme = Yii::createObject($this->theme);
}
} /**
* Renders a view.
* 渲染一个视图
* The view to be rendered can be specified in one of the following formats:
*
* - path alias (e.g. "@app/views/site/index");
* 路径别名
* - absolute path within application (e.g. "//site/index"): the view name starts with double slashes.
* The actual view file will be looked for under the [[Application::viewPath|view path]] of the application.
* 绝对路径，会在[Application::viewPath|view path]下查找文件
* - absolute path within current module (e.g. "/site/index"): the view name starts with a single slash.
* The actual view file will be looked for under the [[Module::viewPath|view path]] of the [[Controller::module|current module]].
* 模块下的绝对路径，会在[Module::viewPath|view path]下查找文件
* - relative view (e.g. "index"): the view name does not start with `@` or `/`. The corresponding view file will be
* looked for under the [[ViewContextInterface::getViewPath()|view path]] of the view `$context`.
* 相对路径，会在[ViewContextInterface::getViewPath()|view path]下查找文件
* If `$context` is not given, it will be looked for under the directory containing the view currently
* being rendered (i.e., this happens when rendering a view within another view).
*
* @param string $view the view name. 视图名称
* @param array $params the parameters (name-value pairs) that will be extracted and made available in the view file.
* 视图中应用参数
* @param object $context the context to be assigned to the view and can later be accessed via [[context]]
* in the view. If the context implements [[ViewContextInterface]], it may also be used to locate
* the view file corresponding to a relative view name. 对应情景
* @return string the rendering result
* @throws InvalidParamException if the view cannot be resolved or the view file does not exist.
* @see renderFile()
*/
public function render($view, $params = [], $context = null)
{
$viewFile = $this->findViewFile($view, $context);//查找视图文件路径
return $this->renderFile($viewFile, $params, $context);//渲染视图文件
} /**
* Finds the view file based on the given view name.通过视图文件名查找视图文件
* @param string $view the view name or the path alias of the view file. Please refer to [[render()]]
* on how to specify this parameter. 视图名称或路径视图文件的别名
* @param object $context the context to be assigned to the view and can later be accessed via [[context]]
* in the view. If the context implements [[ViewContextInterface]], it may also be used to locate
* the view file corresponding to a relative view name. 对应情景
* @return string the view file path. Note that the file may not exist. 文件路径
* @throws InvalidCallException if a relative view name is given while there is no active context to
* determine the corresponding view file.
*/
protected function findViewFile($view, $context = null)
{
if (strncmp($view, '@', ) === ) {
// e.g. "@app/views/main" 判断是否是别名路径，是则获取真实路径
$file = Yii::getAlias($view);
} elseif (strncmp($view, '//', ) === ) {
// e.g. "//layouts/main" 以//开始，查找文件路径，拼接视图文件路径
$file = Yii::$app->getViewPath() . DIRECTORY_SEPARATOR . ltrim($view, '/');
} elseif (strncmp($view, '/', ) === ) {
// e.g. "/site/index"
if (Yii::$app->controller !== null) {
//以/开始，且控制器存在，查找控制器对应的文件目录，拼接路径
$file = Yii::$app->controller->module->getViewPath() . DIRECTORY_SEPARATOR . ltrim($view, '/');
} else {
throw new InvalidCallException("Unable to locate view file for view '$view': no active controller.");
}
} elseif ($context instanceof ViewContextInterface) {
//对应情景存在 查找文件路径，拼接视图文件路径
$file = $context->getViewPath() . DIRECTORY_SEPARATOR . $view;
} elseif (($currentViewFile = $this->getViewFile()) !== false) {
//当前渲染文件存在，拼接路径
$file = dirname($currentViewFile) . DIRECTORY_SEPARATOR . $view;
} else {
throw new InvalidCallException("Unable to resolve view file for view '$view': no active view context.");
} if (pathinfo($file, PATHINFO_EXTENSION) !== '') {
return $file;//视图文件的扩展名不为空，返回扩展名
}
$path = $file . '.' . $this->defaultExtension; //给视图文件添加扩展名
if ($this->defaultExtension !== 'php' && !is_file($path)) {
$path = $file . '.php';
} return $path;//返回路径
} /**
* Renders a view file.
* 渲染一个视图文件。
* If [[theme]] is enabled (not null), it will try to render the themed version of the view file as long
* as it is available.
* 如果[theme]可用，将渲染视图文件的主题版本直到[theme]不可用
* The method will call [[FileHelper::localize()]] to localize the view file.
* 调用[FileHelper::localize()]方法本地化视图文件
* If [[renderers|renderer]] is enabled (not null), the method will use it to render the view file.
* Otherwise, it will simply include the view file as a normal PHP file, capture its output and
* return it as a string.
* 如果[[renderers|renderer]]启用，该方法将用它来渲染视图文件。否则，将视图文件作为一个正常的PHP文件包含进来，获取其输出并返回一个字符串。
* @param string $viewFile the view file. This can be either an absolute file path or an alias of it.
* 视图文件。可以是绝对路径或它的别名。
* @param array $params the parameters (name-value pairs) that will be extracted and made available in the view file.
* 视图文件执行的参数
* @param object $context the context that the view should use for rendering the view. If null,
* existing [[context]] will be used.
* 用于渲染视图的上下文
* @return string the rendering result
* @throws InvalidParamException if the view file does not exist
*/
public function renderFile($viewFile, $params = [], $context = null)
{
$viewFile = Yii::getAlias($viewFile);//处理输入的视图文件名 if ($this->theme !== null) {
$viewFile = $this->theme->applyTo($viewFile);//如果theme非空，应用到视图文件
}
if (is_file($viewFile)) {
$viewFile = FileHelper::localize($viewFile);//本地化视图文件
} else {
throw new InvalidParamException("The view file does not exist: $viewFile");
} $oldContext = $this->context;
if ($context !== null) {
$this->context = $context;
}
$output = '';
$this->_viewFiles[] = $viewFile;//记录当前渲染文件 if ($this->beforeRender($viewFile, $params)) {//如果前置事件执行成功
Yii::trace("Rendering view file: $viewFile", __METHOD__);//记录trace信息
$ext = pathinfo($viewFile, PATHINFO_EXTENSION);//视图文件扩展名
if (isset($this->renderers[$ext])) {//视图文件的扩展名是否支持
if (is_array($this->renderers[$ext]) || is_string($this->renderers[$ext])) {
$this->renderers[$ext] = Yii::createObject($this->renderers[$ext]);
}
/* @var $renderer ViewRenderer */
$renderer = $this->renderers[$ext];//赋值view渲染器对象
$output = $renderer->render($this, $viewFile, $params);//渲染视图文件
} else {//视图文件不是支持的类型，以普通php文件处理
$output = $this->renderPhpFile($viewFile, $params);
}
$this->afterRender($viewFile, $params, $output);
} array_pop($this->_viewFiles);
$this->context = $oldContext; return $output;
}