致命错误：不在对象上下文说明中时使用$ this？

Question

I'm getting this strange error which I have never got before.

Fatal error: Using $this when not in object context

Chat.php (class)

<?php
class Chat {
private $_data = array(),
        $_db;

public function __construct($row){
    $this->_db = DB::getInstance();
    $this->_data = $row;

}

public function send($fields = array()) {
    $this->_db->insert('messages', $fields); <------- ERROR
 }

When I call the send function like this:

Chat::send(array(
'message' => Input::get('message'),
'author' => $user->data()->username,
'ts' => date('Y-m-d H:i:s')
));

The error pops up.

Answer 1

You need to create an object with new , so that there will be a $this object:

$chat = new Chat($row);
$chat->Send(array(
    'message' => Input::get('message'),
    'author' => $user->data()->username,
    'ts' => date('Y-m-d H:i:s')
));

You don't create the database connection until the constructor is called, which happens when new is used.

Answer 2

You are accessing the send() function static ally (although it is not defined as such) by using the operator :: . Because you are using $this in your function, it expects an object to have been created by the __construct() method, but this does not happen in a static function . If you create a new instance of the Chat object using $chat = new Chat($row) then $this will refer to that object in the function, which should be called using the -> operator as in $chat->send() .

// Create a new Chat object using __construct( $row ), creating $this
$chat = new Chat( $row );
// Call send() method on the $chat object
$chat->send( array() ); // add your data

See the documentation for the static keyword :

Because static methods are callable without an instance of the object created, the pseudo-variable $this is not available inside the method declared as static.