注意:以非静态方式访问静态属性DBController::$conn

Question

{
class DBController 
private $host = "localhost";
private $user = " ";
private $password = " ";
private $database = " ";
private static $conn;
function __construct() {
$this->conn = $this->connectDB();
if(!empty($this->conn)) {
$this->selectDB();
}
}
function connectDB() {
$conn = mysqli_connect($this->host,$this->user,$this->password,$this->database);
return $conn;
}
function selectDB() {
mysqli_select_db($this->conn, $this->database);
}
function numRows($query) {
$result  = mysqli_query($this->conn, $query);
$rowcount = mysqli_num_rows($result);
return $rowcount;
}
}
}

我有上述类别的数据库控制器，但我收到了如下所述的通知或警告：

注意：在C:\abc\DBController.php的第11行访问静态属性DBController:：$conn作为非静态属性($this->conn=$this->connectDB((；(

注意：在C:\abc\DBController.php的第23行访问静态属性DBController:：$conn作为非静态属性(mysqli_select_db($this->conn，$this->database(；(

注意：在C:\abc\DBController.php的第27行访问静态属性DBController:：$conn作为非静态属性($result=mysqli_query($this->conn，$query(；(

Answer 1

$this->conn应为static::$conn

或

从private static $conn;中删除static关键字