在非对象上调用成员函数 getAttribute()

Question

这是我得到的错误：

Fatal error: Call to a member function getAttribute() on a non-object 
in /home/a4688869/public_html/random/index.php 
on line 45

这是一张图片：http://prntscr.com/5rum9z

该功能适用于前几张，但在显示几张图片后就会中断。本质上，代码会生成一个随机 html。我使用 cURL 获取 html，然后用一个函数解析它，然后 select 来自站点的图像，然后重复该过程，直到我得到 5 张图像。

我的代码

$original_string = '123456789abh';
$random_string = get_random_string($original_string, 6);
//Generates a random string of characters and returns the string
function get_random_string($valid_chars, $length)
{

    $random_string = ""; // start with an empty random string
    $num_valid_chars = strlen($valid_chars); // count the number of chars in the valid chars string so we know how many choices we have

    // repeat the steps until we've created a string of the right length
    for ($i = 0; $i < $length; $i++)
    {
        $random_pick = mt_rand(1, $num_valid_chars); // pick a random number from 1 up to the number of valid chars

        // take the random character out of the string of valid chars
        // subtract 1 from $random_pick because strings are indexed starting at 0, and we started picking at 1
        $random_char = $valid_chars[$random_pick-1];
        $random_string .= $random_char; // add the randomly-chosen char onto the end of our string so far
    }

    return $random_string;
}


//Parses the random website and returns the image source
function websearch($url){
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    $html = curl_exec($ch);
    curl_close($ch);

    $dom = new DOMDocument;
    @$dom->loadHTML($html); // Had to supress errors

    $img = $dom->getElementsByTagName('img')->item(1); //Get just the second picture
    $src = $img->getAttribute('src'); //Get the source of the picture

    return $src;
}

显示 html

的代码部分

for ($i = 0; $i < $perpage; $i++){
            $random_string = get_random_string($original_string, 6);
            $src = websearch('http://prntscr.com/' . $random_string);
            while( $src == "http://i.imgur.com/8tdUI8N.png"){
                $random_string = get_random_string($original_string, 6);
                $src = websearch('http://prntscr.com/' . $random_string);
            }
                ?>

<img src="<?php echo $src; ?>">
<p><a href="<?php echo $src; ?>"><?php echo $src; ?></a></p>
<?php if ($i  != $perpage - 1){ // Only display the hr if there is another picture after it ?>
<hr>
<?php }}?>

Answer 1

每当您遇到“非对象”错误时，那是因为您在不是对象的变量上调用方法。

这可以通过始终检查您的 return 值来解决。它可能不是很优雅，但计算机是愚蠢的，如果你想让你的代码工作，那么你必须始终确保它做你想做的事。

$img = $dom->getElementsByTagName('img')->item(1);
if ($img === null) {
    die("The image was not found!");
}

您还应该养成阅读所用内容文档的习惯（在本例中为 return 值）。

正如您在 DOMNodelist::item 页面上看到的，如果方法失败，return 值是 null:

Return Values

The node at the indexth position in the DOMNodeList, or NULL if that is not a valid index.