Question

我被XDocument再次难倒了。当class属性值为“high”（和“low”）时，我试图提取温度元素的值（本例中为12）

我的XML的一个子集：

<forecastGroup>
    <forecast>
      <temperatures>
          <textSummary>Low plus 2. High 12.</textSummary>
          <temperature unitType="metric" units="C" class="high">12</temperature>
          <temperature unitType="metric" units="C" class="low">2</temperature>
      </temperatures>
    </forecast>
    ...etc.
    <forecast>
          <temperature unitType="metric" units="C" class="high">15</temperature>
          <temperature unitType="metric" units="C" class="low">3</temperature>
    </forecast>
<forecastGroup>

到目前为止

代码：

XDocument loaded = XDocument.Parse(strInputXML);
foreach (var forecast in loaded.Descendants("forecastGroup").Elements("forecast"))
{
   //existing code doing stuff here using the XDocument loaded
   High = "this is where I'm lost";
}

我似乎尝试过尝试选择元素，属性和后代的所有组合“，但我不知所措。

Answer 1

您只需在Linq to XML查询中添加Where()过滤器：

XDocument loaded = XDocument.Parse(strInputXML);
var matchingForecasts = loaded.Descendants("temperature")
                              .Where(x => (string)x.Attribute("class") == "high");
foreach (var forecast in matchingForecasts)
{
    //do something
    string temperature = forecast.Value;
}

或者，您可以查看class循环中的每个foreach属性值，这更接近您原来的方法：

foreach (var forecast in loaded.Descendants("temperature"))
{
    //existing code doing stuff here using the XDocument loaded
    if (forecast.Attribute("class").Value == "high")
    {
        //do something
        string temperature = forecast.Value;
    }
}

Answer 2

loaded.Descendants("temperature")
.Where(d => d.Attribute("class").Value.Equals("high")).First().Value

Answer 3

要提取循环中的高位，可以使用

行

var high = (int)forecast.Element("temperatures")
                        .Elements("temperature")
                        .Where(temp => temp.Attribute("class").Value == "high")
                        .First();

当然，您可以使用Linq-to-XML将整个XML树简单地投影到适当的对象图中，而无需在循环中明确地将其分开，但您应该能够朝着这个方向前进。它可能最终看起来像

var forecasts = from forecast in loaded.Descendants("forecast")
                let temps = forecast.Element("temperatures")
                let high = temps.Elements("temperature").Where(t => t.Attribute("class").Value == "high").First()
                let low = temps.Elements("temperature").Where(t => t.Attribute("class").Value == "low").First()
                select new
                {
                    Temperatures = new
                    {
                        Summary = temps.Element("textSummary").Value,
                        High = new
                        {
                            UnitType = high.Attribute("unitType").Value,
                            Units = high.Attribute("units").Value,
                            Value = (int)high
                        },
                        Low = new
                        {
                            UnitType = low.Attribute("unitType").Value,
                            Units = low.Attribute("units").Value,
                            Value = (int)low
                        },
                    }
                };

Answer 4

示例XML文件无效，因为它未正确关闭。

 <forecastGroup>
    <forecast>
      <temperatures>
          <textSummary>Low plus 2. High 12.</textSummary>
          <temperature unitType="metric" units="C" class="high">12</temperature>
          <temperature unitType="metric" units="C" class="low">2</temperature>
      </temperatures>
    </forecast>
    ...etc.
    <forecast>
          <temperature unitType="metric" units="C" class="high">15</temperature>
          <temperature unitType="metric" units="C" class="low">3</temperature>
    </forecast>
<forecastGroup>   // <= this needs to be </forecastGroup>

Answer 5

您可以尝试使用XPath：

using System.Xml.XPath;
...
string xpathExpression = "forecastGroup/forecast//temperature[@class='high']";
foreach (XElement el in loaded.XPathSelectElements(xpathExpression))
{
    int highTemperature = Int32.Parse(el.Value);
}

搜索表达式可能更短（"//temperature[@class='high']"），但更详细地了解值的位置。

如果要使用“高”或“低”类属性值过滤温度，可以使用此xpath表达式：

"forecastGroup/forecast//temperature[@class='high' or @class='low']"

如果您想根据@class属性决定做什么，可以使用以下代码：

string xpathExpression = "forecastGroup/forecast//temperature[@class='high' or @class='low']";
foreach (XElement el in loaded.XPathSelectElements(xpathExpression))
{
    int temperature = Int32.Parse(el.Value);
    if (el.Attribute("class").Value == "low")
    {
        // do sth with low value
    }
    else
    {
        // do sth with high value
    }
}

提取属性等于特定值的元素的值

5 个答案: