down00112 2017-03-16 19:01
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致命错误:在null [关闭]上调用成员函数test()

<?php
class database{
    private static $instance;
    public function __construct()
    {       
    }   
    static public function newinstance()
    {

        if(!self::$instance)
        {
            self::$instance = new self();
        }
        return self::$instance;
    }
    public function conn()
    {
    mysql_connect('localhost','root','') or die("database connection error".mysql_error());
    mysql_select_db('user') or die("cannot select db".mysql_error());

    }
    public function test()
    {
        echo "Public function test";
    }

}
$db=database::newinstance()->conn();
$db->test();

?>

When i rung this php file i got this error:Fatal error: Call to a member function test() on null , what could be the problem?Thank you!

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3条回答 默认 最新

  • doulang6013 2017-03-16 19:04
    关注

    conn() method returns nothing, which you have assigned to $db. Try with:

    $db = database::newinstance();
    $db->conn();
    $db->test();
    

    or you can return $this in conn() method and use your syntax:

    public function conn()
    {
      mysql_connect('localhost','root','') or die("database connection error".mysql_error());
      mysql_select_db('user') or die("cannot select db".mysql_error());
      return $this;
    }
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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