Question

我在PHP代码中遇到了一些问题。我有三个名为

的类

DatabaseObject
文件
user_picture

从父类到子类的继承树是 DatabseObect-＆gt; File-＆gt; user_picture 。在 user_picture 中，我有一个静态属性$ table_name，我用它来了解每个类的数据库表名，并在 DatabaseObject 类中有一些常见的数据库函数。我正在使用的函数的代码在这里

DatabaseObject类的代码

public static function find_by_field($field="", $value="")
{
    $result_array = self::find_by_sql("SELECT * FROM ".static::$table_name." WHERE {$field} = '".$value."'"); //Line 52
    if(empty($result_array))
    {
        return false;
    }
    else
    {
        $object = static::instantiate(array_shift($result_array));
        return $object;
    }
}

文件类代码

public $errors=array();

public $file_before_upload; // General file tyoe that has been uploaded from the form
public $id = 0;
public $size;
public $file_name;
public $file_type;
public $user_id;

protected $temp_path;
//protected static $upload_dir="";

protected $upload_errors = array(
    // http://www.php.net/manual/en/features.file-upload.errors.php
    UPLOAD_ERR_OK               => "No errors.",
    UPLOAD_ERR_INI_SIZE     => "Larger than upload_max_filesize.",
    UPLOAD_ERR_FORM_SIZE    => "Larger than form MAX_FILE_SIZE.",
    UPLOAD_ERR_PARTIAL      => "Partial upload.",
    UPLOAD_ERR_NO_FILE      => "No file.",
    UPLOAD_ERR_NO_TMP_DIR => "No temporary directory.",
    UPLOAD_ERR_CANT_WRITE => "Can't write to disk.",
    UPLOAD_ERR_EXTENSION    => "File upload stopped by extension."
);
public static function get_file_by_user($id = 0){
       return DatabaseObject::find_by_field("user_id",$id); //Line 164
    }

user_picture类的代码

protected static $table_name = "user_images";
    protected static $db_fields = array('id','file_name','file_type','size','user_id');

    public static $upload_dir ="uploads".DS."user_img";
    protected static $file_upload_limit = 15;


    public static function get_image_by_user($id = 0)
    {
        return File::get_file_by_user($id);  //Line 45
    }

我在 user_picture 中调用上层函数的位置是

$user_image = user_picture::get_image_by_user($session->user_id);

$user_picture_path="";

if(!$user_image)
{
    $user_picture_path = $user_image::upload_dir.DS."default.png";
}
else{
    $user_picture_path = $user_image::file_path(); //Line 28
}

此代码给出了以下错误

致命错误：未捕获错误：访问未声明的静态属性：C：\ xampp \ htdocs \ inventory-management \ includes \ database \ DatabaseObject.php中的DatabaseObject :: $ table_name：52   堆栈跟踪：

0 C：\ xampp \ htdocs \ inventory-management \ includes \ general \ File.php（164）：DatabaseObject :: find_by_field（'user_id'，'29'）

1 C：\ xampp \ htdocs \ inventory-management \ includes \ user \ user_picture.php（45）：File :: get_file_by_user（'29'）

2 C：\ xampp \ htdocs \ inventory-management \ public \ admin \ layouts \ admin \ header \ Navigation.php（28）：user_picture :: get_image_by_user（'29'）

3 C：\ xampp \ htdocs \ inventory-management \ public \ admin \ layouts \ admin \ header \ admin_header.php（21）：require_once（'C：\ xampp \ htdocs ...'）

4 C：\ xampp \ htdocs \ inventory-management \ public \ admin \ add_page_category.php（44）：require_once（'C：\ xampp \ htdocs ...'）

5 {main}     抛出 C：\ xampp \ htdocs \ inventory-management \ includes \ database \ DatabaseObject.php 52

请有人帮忙！

谢谢，

Answer 1

您必须致电self而不是Database::和File::

public static function get_image_by_user($id = 0)
{
    return self::get_file_by_user($id);  //Line 45
}

public static function get_file_by_user($id = 0){
   return self::find_by_field("user_id",$id); //Line 164
}

工作示例：

class A {
    static public function foo() {
        var_dump(static::$bar);
    }
}
class B extends A {
    static protected $bar = "12";

    static public function zoo(){
        self::foo();
    }
}

B::zoo();

不工作的例子：

class A {
    static public function foo() {
        var_dump(static::$bar);
    }
}
class B extends A {
    static protected $bar = "12";

    static public function zoo(){
        A::foo();
    }
}

B::zoo();

无法从PHP中的父静态方法访问子静态属性

1 个答案: