php - PHP-在null上调用成员函数query()-错误

This question already has answers here:

Fatal error: Call to a member function query() on null
（2个答案）
两年前关闭。
我有以下php代码用于连接到我的数据库：

<?php
class MY_SQL{
    private $username;
    private $password;
    private $conn;

    public function __construct($SERVERNAME){
        $this->username = "username";
        $this->password = "password";

        if($SERVERNAME == "data_"){
            $server = "Servername";
        }
        else {
            $server = $SERVERNAME;
        }

        // Create connection
        $conn = new mysqli($server, $this->username, $this->password);

        // Check connection
        if ($conn->connect_error) {
            die("Connection failed: " . $conn->connect_error);
        }
    }

    public function SQLCommand($cmd) {
        if ( $this->conn->query($cmd) === TRUE ) {
            echo "New record created successfully";
        } else {
            echo "Error: " . $cmd . "<br>" . $conn->error;
        }
    }
}

$sql = "INSERT INTO _test(test1, test2) VALUES ('hello','hi');";

        $database = new MY_SQL("Servername");
        $database->SQLCommand($sql);
?>

我得到以下错误：
致命错误：对null调用成员函数query（）
怎么了？

最佳答案

$this->conn = $conn; in __construct()

关于php - PHP-在null上调用成员函数query()-错误，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/42952514/