Question

我正在扩展一个有两个抽象方法的抽象类。当我尝试实例化子类时，我得到以下错误，

 PHP Fatal error:  Uncaught Error: Cannot call abstract method GetAnswer::GetAnswer()

当我注释掉父母和孩子的GetAnswer()时，工作正常。

PHP版本：XAMPP中的7.0.2，在Wondows 8.1上运行。

父类文件app-getAnswer-base.php如下

<?php
abstract class GetAnswer{
    abstract public function GetAnswer($Username, $QuestionnaireID, $QuestionID);
    abstract public function GetAnswers($Username, $QuestionnaireID);
}

子类文件app-getAnswer-db-direct.php如下

<?php
require_once 'config-db-login.php';
require_once 'app-getAnswer-base.php';

class GetAnswer_SQLSelect extends GetAnswer {

    public function GetAnswer($Username, $QuestionnaireID, $QuestionID){
        return null;
    }    

    public function GetAnswers($Username, $QuestionnaireID){
        $connection = new mysqli(dbLogin::$db_hostname, dbLogin::$db_username, dbLogin::$db_password, dbLogin::$db_database);

        if ($connection->connect_error) die($connection->connect_error);

        $query = "SELECT `QuestionID`, `Answer` FROM `answerstore`.`answers` AS a JOIN  `answerstore`.`participants` AS b ON a.`ParticipantID` = b.`ParticipantID` WHERE a.`QuestionnaireID` = '$QuestionnaireID' AND b.`Username`='$Username'";

        $result = $connection->query($query);
        $connection->close();

        return $result;    
    }
}

Answer 1

我认为当您尝试实例化Child类时，它会从Parent类（GetAnswer()）调用GetAnswer方法，因为它的工作方式与构造函数类似。 / p>

尝试将方法名称更改为其他名称。

Answer 2

您必须实例化具体类'GetAnswer_SQLSelect'，然后调用方法'GetAnswer'。

$GetAnswer_SQLSelect = new GetAnswer_SQLSelect(); //create new instance.
$GetAnswer_SQLSelect->GetAnswer($param1, $param2, $param3); //invoke method.

未捕获错误：无法调用抽象方法（PHP致命错误）

2 个答案: