为什么我无法在php中获取XML文件的第一个子值

Question

I used an XMLHttpRequest object to retrieve data from a PHP response.

Then, I created an XML file:

<?xml version="1.0" encoding="UTF-8"?>
<persons>
    <person>
        <name>Ce</name>
        <gender>male</gender>
        <age>24</age>
    </person>
    <person>
        <name>Lin</name>
        <gender>female</gender>
        <age>25</age>
    </person>
</persons>

In the PHP file, I load the XML file and try to echo tag values of "name."

$dom = new DOMDocument("1.0");
$dom -> load("test.xml");
$persons = $dom -> getElementsByTagName("person");
foreach($persons as $person){
    echo $person -> childNodes -> item(0) -> nodeValue;
}

But the nodeValue returned is null. However, when I change to item(1), the name tag values can be displayed. Why?

Answer 1

Using DOM you need to get the right element to pick up the name, child nodes include all sorts of things including whitespace. The node 0 your trying to use is null because of this. So for DOM...

$dom = new DOMDocument("1.0");
$dom -> load("test.xml");
$persons = $dom -> getElementsByTagName("person");
foreach($persons as $person){
   $name = $person->getElementsByTagName("name");
   echo $name->item(0)->nodeValue.PHP_EOL;
}

If your requirements are as simple as this, you could alternatively use SimpleXML...

$sxml = simplexml_load_file("test.xml");
foreach ( $sxml->person as $person )    {
    echo $person->name.PHP_EOL;
}

This allows you to access elements as though they are object properties and as you can see ->person equates to accessing <person>.