尝试访问类内部的错误

Question

错误：未捕获错误：调用成员函数prepare（）on null（...）fetch_my_db-＆gt; fetch（）＃1 {main}抛出。

我正在尝试在类中访问我的数据库连接，但是我得到了这个错误，如果我复制＆amp;粘贴我的try和catch类fetch_my_db内部的连接。我需要一些帮助。

File Index.php Code;

<?php

try {
    $ligação = new PDO('mysql:host=localhost;dbname=mydatabase;charset=utf8', 'user', 'password');
    $ligação->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $erro) {
    echo $erro->getMessage();
    die();
}

class fetch_my_db {
    public function fetch() {
        $var = 'product';
        $sth = $ligação->prepare('SELECT * FROM mytable WHERE type LIKE :parameter LIMIT 10');
        $sth->bindParam(':parameter', $var, PDO::PARAM_STR);
        $sth->execute();
        $i = 1;
        while ($r = $sth->fetch()) {
            echo $r["title"] . " <br>";
            echo $r["type"] . " <br>";
            echo $r["price"] . " <br>";
        }
    }
}

$gotosql = new fetch_my_db();
$gotosql->fetch();

?>