MySQLi类，未定义变量[关闭]

I have a MySQLi class that I am using but when I initliaze it and then try and perform a query, I get the following error:

Notice: Undefined variable: MySQLi in ...

Im new to mysqli and classes

Here is my Class:

<?PHP
    class DB
    {
        private static $instance;
        private $MySQLi;

        private function __construct(array $dbOpt)
        {
            $this->MySQLi = @ new MySQLi($dbOpt['db_host'],$dbOpt['db_user'],$dbOpt['db_pass'],$dbOpt['db_name']);

            if(mysqli_connect_errno()) {
                throw new Exception("Database connection error");   
            }

            $this->MySQLi->set_charset("utf8");
        }

        public static function init(array $dbOpt)
        {
            if(self::$instance instanceof self) {
                return false;   
            } else {
                self::$instance = new self($dbOpt);
            }
        }

        public static function getMySQLiObj() {
            return self::$instance->$MySQLi;    
        }

        public static function query($q) {
/* This is the line that fails */
            return self::$instance->$MySQLi->query($q); 
        }

        public static function escape($str) {
            return self::$instance->$MySQLi->real_escape_string(htmlspecialchars($str));    
        }
    }
?>

Here is my query:

//Connect to database
DB::init($dbOpt);

$result = DB::query("SELECT * FROM myTable");

if(!$result) {
    echo "MySQLi Query failed"; 
}
else {
//handle query
}

I have commented above the line that fails.

Remove the $. The code of your DB::query() method should look like this:

return self::$instance->MySQLi->query($q); 

Note, a static var will be accsessed this way:

Classname::$varname

an instance var will be accessed as follows:

$instance = new Classname();
$instance->varname;

You don't need the $ on the ->$MySQLi in that line.

$ is only needed on variables outside classes. You have this error on several other lines in the code as well.