Question

我正在尝试使用try catch块中的属性。 try catch块是在类内部。我想扩展一个特定的类，使其成为处理异常的类的子类。问题是，当我尝试使用子类中的那些变量时，它总是表示未定义。我必须删除这两个类才能捕获属性。通过在try catch块之外添加一个return语句（我添加了返回1）来阅读其他一些答案之后，它似乎无法正常工作并且它总是表示未定义的变量。有什么帮助吗？

语言是php

源代码没有类完美无缺：

    try
    {
        //$pdo variable to insert PDO object information
        $pdo = new PDO('mysql:host=localhost;dbname=studenti', 'root', '');

        //Set php to catch exceptions
        $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

        //Set UTF-8 for character encodings
        $pdo->exec('SET NAMES "utf8"');
    }
    //Catch error if unable to connect
    catch(PDOException $e)
    {
        //error variable
        $error = 'Unable to connect with database. ' . $e->getMessage();

        //include file once and show on screen error message
        include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
        //Exit and don't process further
        exit();
    }

    //Another Exception handling
    try
    {
        //Select statement
        $sql = 'SELECT * FROM dega';
        $select = $pdo->query($sql);
    }
    catch(PDOException $e)
    {
        //error variable
        $error = 'Unable to select table. ' . $e->getMessage();

        //include file once and show on screen error message
        include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';

        //Exit and don't process further
        exit();
    }

源代码 with 类不起作用：

<?php
    //PDO class, connection with MySQL database
    class Connect
    {
        function connection()
        {
        $pdo = null;
            try
            {
                //$pdo variable to insert PDO object information
                $pdo = new PDO('mysql:host=localhost;dbname=studenti', 'root', '');

                //Set php to catch exceptions
                $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

                //Set UTF-8 for character encodings
                $pdo->exec('SET NAMES "utf8"');
            }
            //Catch error if unable to connect
            catch(PDOException $e)
            {
                //error variable
                $error = 'Unable to connect with database. ' . $e->getMessage();

                //include file once and show on screen error message
                include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
                //Exit and don't process further
                exit();
            }
        }
    }

    class Select extends Connect
    {
        function selection()
        {
            //Another Exception handling
            try
            {
                //Select statement
                $sql = 'SELECT * FROM dega';
                $select = $pdo->query($sql);
            }
            catch(PDOException $e)
            {
                //error variable
                $error = 'Unable to select table. ' . $e->getMessage();

                //include file once and show on screen error message
                include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';

                //Exit and don't process further
                exit();
            }
        }
    }

    //Output if successful
    $error = 'Database connection established.';
    include $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
?>

Answer 1

你没有子类。 Object Inheritance
您没有任何属性。 Properties

了解Classes and Objects。

class Connect
    {
    protected $pdo = null;

    public function connection()
        {
        $pdo = null;
        try
            {
            $this->pdo = new PDO('mysql:host=localhost;dbname=studenti', 'root', '');
            $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $this->pdo->exec('SET NAMES "utf8"');
            } catch (PDOException $e)
            {
            $error = 'Unable to connect with database. ' . $e->getMessage();
            include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
            exit();
            }
        }
    }

class Select extends Connect
    {

    function selection()
        {
        try
            {
            $sql = 'SELECT * FROM dega';
            $select = $this->pdo->query($sql);
            } catch (PDOException $e)
            {
            $error = 'Unable to select table. ' . $e->getMessage();
            include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
            exit();
            }
        }
    }

Answer 2

将$pdo放在connection()之前：

class Connect
{
    protected $pdo = null; // or var $pdo = null;
    function connection()
    {
     ...

在函数内部，它是一个局部变量而不是类级属性。

修改：
PHP需要$this-><class-variable>来访问函数内的类属性。（查看@ Sectus的答案如下。）只是使用$ pdo即时创建一个局部变量（在两个方法中）但仅在selection()中给出错误，因为这是query()被调用的地方首先初始化PDO()对象。

不能在try catch块之外使用属性

2 个答案: