PHP - 私有類變量給錯誤：未定義的變量

Question

我收到錯誤「未定義的變量：區間在C：\ WAMP \ WWW \ DGC \類\ DateFilter.php」

這裏是我的DateFilter碼類：

class DateFilter extends Filter 
{ 
    //@param daysOld: how many days can be passed to be included in filter 
    //Ex. If daysOld = 7, everything that is less than a week old is included 
    private $interval; 

    public function DateFilter($daysOld) 
    { 
     echo 'days old' . $daysOld .'</ br>'; 
     $interval = new DateInterval('P'.$daysOld.'D'); 
    } 


    function test() 
    { 
     echo $interval->format("%d days old </br>"); 
     //echo 'bla'; 
    } 

} 

當我創建DateFilter類和呼叫測試的新實例（）它給我的錯誤。我意識到這意味着變量還沒有被初始化，但我知道構造函數被調用，因爲我在那裏放置了一個echo語句，並且它被輸出。

我也嘗試過： $ this :: $ interval-> format（...）; self :: $ interval-> format（...）; 但它沒有奏效。

我知道這可能是一個簡單的修復，對於noob問題抱歉。我不敢相信這讓我難堪。

Answer 1

您必須使用$this->interval訪問PHP中的成員變量interval。見PHP: The Basics

class DateFilter extends Filter 
{ 
    private $interval; // this is correct. 

    public function DateFilter($daysOld) 
    { 
     $this->interval = new DateInterval('P'.$daysOld.'D'); // fix this 
    } 

    function test() 
    { 
     echo $this->interval->format("%d days old </br>");  // and fix this 
    } 
} 

Answer 2

function test() 
{ 
    echo $this->interval->format("%d days old </br>"); 
} 

Answer 3

試圖

public var $interval; 

和

echo $this->interval; 

Answer 4

$interval是本地功能。 $this->interval引用您的私人財產。

class DateFilter extends Filter 
{ 
    //@param daysOld: how many days can be passed to be included in filter 
    //Ex. If daysOld = 7, everything that is less than a week old is included 
    private $interval; 

    public function DateFilter($daysOld) 
    { 
     echo 'days old' . $daysOld .'</ br>'; 
     $this->interval = new DateInterval('P'.$daysOld.'D'); 
    } 


    function test() 
    { 
     echo $this->interval->format("%d days old </br>"); 
     //echo 'bla'; 
    } 

}