php - 多维数组迭代

Question

假设您有以下数组:

$nodes = array(
    "parent node",
    "parent node",
    array(
        "child node",
        "child node",
        array(
            "grand child node",
            "grand child node")));

如何将其转换为 XML 字符串，使其看起来像:

<node>
    <node>parent node</node>
    <node>parent node</node>
    <node>
        <node>child node</node>
        <node>child node</node>
        <node>
            <node>grand child node</node>
            <node>grand child node</node>
        </node>
    </node>
</node>

一种方法是通过递归方法，例如:

function traverse($nodes)
{
    echo "<node>";

    foreach($nodes as $node)
    {
        if(is_array($node))
        {
            traverse($node);
        }
        else
        {
            echo "<node>$node</node>";
        }
    }

    echo "</node>";
}

traverse($nodes);

不过，我正在寻找一种使用迭代的方法。

Answer 1

您可以使用 Iterator迭代数组，然后生成所需的输出:

class TranformArrayIterator extends RecursiveIteratorIterator
{
    protected function indent()
    {
        echo str_repeat("\t", $this->getDepth());
        return $this;
    }
    public function beginIteration()
    {
        echo '<nodes>', PHP_EOL;
    }
    public function endIteration()
    {
        echo '</nodes>', PHP_EOL;
    }
    public function beginChildren()
    {
        $this->indent()->beginIteration();
    }
    public function endChildren()
    {
        $this->indent()->endIteration();
    }
    public function current()
    {
        return sprintf('%s<node>%s</node>%s',
                       str_repeat("\t", $this->getDepth() +1),
                       parent::current(),
                       PHP_EOL);
    }
}

然后像这样组装它:

$iterator = new TranformArrayIterator(new RecursiveArrayIterator($nodes));

foreach($iterator as $val) {
    echo $val;
}

输出

<nodes>
        <node>parent node</node>
        <node>parent node</node>
        <nodes>
                <node>child node</node>
                <node>child node</node>
                <nodes>
                        <node>grand child node</node>
                        <node>grand child node</node>
                </nodes>
        </nodes>
</nodes>

要在使用 $key => $val 时清空 $key，请将其添加到 TraverseArrayIterator

public function key()
{ 
    return '';
}

由于您的目标似乎是生成 XML，因此您还可以将 XMLWriter 作为协作者传递给迭代器。这允许对生成的 XML 进行更多控制，并确保输出是有效的 XML:

class TranformArrayIterator extends RecursiveIteratorIterator
{
    private $xmlWriter;

    public function __construct(
        XmlWriter $xmlWriter, 
        Traversable $iterator, 
        $mode = RecursiveIteratorIterator::LEAVES_ONLY , 
        $flags = 0)
    {
        $this->xmlWriter = $xmlWriter;
        parent::__construct($iterator, $mode, $flags);
    }

    public function beginIteration()
    {
        $this->xmlWriter->startDocument('1.0', 'utf-8');
        $this->beginChildren();
    }
    public function endIteration()
    {
        $this->xmlWriter->endDocument();
    }
    public function beginChildren()
    {
        $this->xmlWriter->startElement('nodes');
    }
    public function endChildren()
    {
        $this->xmlWriter->endElement();
    }
    public function current()
    {
        $this->xmlWriter->writeElement('node', parent::current());
    }
}

然后你可以像这样使用它:

$xmlWriter = new XmlWriter;
$xmlWriter->openUri('php://output');
$xmlWriter->setIndent(true);
$xmlWriter->setIndentString("\t");
$iterator = new TranformArrayIterator(
    $xmlWriter,
    new RecursiveArrayIterator($nodes)
);

和 foreach 将产生相同的输出(但添加 XML 序言)