PHP SimpleXML属性值获取指南：理解与实践

// 假设 $c 是一个 SimpleXMLElement 对象，代表 <Cube currency="USD" rate="1.1278"/>
$currencyAttribute = $c->attributes()->currency;

// 此时 $currencyAttribute 是一个 SimpleXMLElement 对象
var_dump($currencyAttribute);
// 输出类似：object(SimpleXMLElement)#3 (1) { [0]=> string(3) "USD" }

// 你可以获取它的名称
echo $currencyAttribute->getName(); // 输出 'currency'

// 隐式转换示例
echo $c->attributes()->currency; // 输出 "USD"
$message = 'Currency: ' . $c->attributes()->currency; // $message 为 "Currency: USD"
$interpolated = "Rate: {$c->attributes()->rate}"; // $interpolated 为 "Rate: 1.1278"

// 使用 (string) 进行显式转换
$currency = (string) $c->attributes()->currency;
$rate = (string) $c->attributes()->rate;

// 使用 strval() 函数进行显式转换
$currency_strval = strval($c->attributes()->currency);
$rate_strval = strval($c->attributes()->rate);

var_dump($currency, $rate); // 此时它们都是字符串类型

<?php

// 模拟获取XML数据，实际应用中可能通过 file_get_contents 或 cURL 获取
$xmlString = <<<XML
<gesmes:Envelope xmlns:gesmes="http://www.gesmes.org/xml/2002-08-01" xmlns="http://www.ecb.int/vocabulary/2002-08-01/eurofxref">
    <gesmes:subject>Reference rates</gesmes:subject>
    <gesmes:Sender>
        <gesmes:name>European Central Bank</gesmes:name>
    </gesmes:Sender>
    <Cube>
        <Cube time="2021-12-13">
            <Cube currency="USD" rate="1.1278"/>
            <Cube currency="JPY" rate="128.19"/>
            <Cube currency="BGN" rate="1.9558"/>
            <Cube currency="CZK" rate="25.401"/>
            <Cube currency="DKK" rate="7.4362"/>
            <Cube currency="GBP" rate="0.85158"/>
            <Cube currency="HUF" rate="367.07"/>
        </Cube>
    </Cube>
</gesmes:Envelope>
XML;

try {
    // 实例化 SimpleXMLElement 对象
    $xml = new \SimpleXMLElement($xmlString);

    // 遍历汇率数据
    // 注意：这里的路径是根据XML结构确定的
    // xml->Cube->Cube 访问的是 <Cube time="2021-12-13">
    // xml->Cube->Cube->Cube 访问的是每个 <Cube currency="..." rate="..."/>
    foreach ($xml->Cube->Cube->Cube as $c) {
        // 显式将属性转换为字符串
        $currency = (string) $c->attributes()->currency;
        $rate = (string) $c->attributes()->rate;

        echo "Currency: {$currency}, Rate: {$rate}\n";

        // 假设有一个处理汇率的函数或方法
        // $this->currency->setCurrencyRate($currency, $rate);
    }
} catch (\Exception $e) {
    echo "Error parsing XML: " . $e->getMessage();
}

// 模拟的 setCurrencyRate 方法，展示如何接收和处理
class CurrencyService
{
    public function setCurrencyRate($currency, $rate)
    {
        // 此时 $currency 和 $rate 已经是字符串，可以安全地用于数据库操作或其他逻辑
        echo "Storing currency: {$currency} with rate: {$rate}\n";
        // 实际应用中会执行数据库插入或更新操作
        // $data = ['currency' => $currency, 'rate' => $rate, 'updated' => new \DateTime()];
        // $this->db->query('INSERT INTO currencies_rates ...', $data);
    }
}

// 再次运行循环，并使用模拟服务
echo "\n--- Using CurrencyService ---\n";
$currencyService = new CurrencyService();
foreach ($xml->Cube->Cube->Cube as $c) {
    $currencyService->setCurrencyRate(
        (string) $c->attributes()->currency,
        (string) $c->attributes()->rate
    );
}

?>