如何使用<<< HTMLDOC ... HTMLDOC格式在Yii PHP中加载面向对象的变量值

i want to use the following code

$mail->Body = <<<HTMLDOC
$this->model->firstname . $this->model->lastname,
today is your lucky day !
your desired product has reached your desired price !
HTMLDOC;

but i get this error: PHP Fatal error: Using $this when not in object context in ...

$this->model->firstname has a value, i checked

You could also try writing the heredoc text like so:

$mail->Body = <<<HTMLDOC
{$this->model->firstname} {$this->model->lastname},
today is your lucky day !
your desired product has reached your desired price !
HTMLDOC;

Either that or you can use views for mail messages (some extensions allow this).