如何将XmlNodeList拆分为两个子XmlNodeList？

Question

我如何将一个XmlNodeList分解成两个较小的XmlNodeList，其中一个具有大小N，而另一个有大小总计- N？

参见下面的一个例子，以及我试图这样做的地方：

    public static void Main(string[] args)
    {
        XmlDocument someDoc = new XmlDocument();
        someDoc.LoadXml(@"<bananas>
                            <banana tasty='yes'></banana>
                            <banana tasty='very'></banana>
                            <banana tasty='amazing'></banana>
                            <banana tasty='mind-blowing'></banana>
                            <banana tasty='disgusting'></banana>
                          </bananas>");
        XmlNodeList bananaNodeList = someDoc.SelectNodes("//banana");
        eatSomeBananas(bananaNodeList, 2);
    }

    /** Splits a XmlNodeList into two XmlNodeList, first one is a slice from 0 to numberOfBananas-1, and the other slice is from numberOfBananas and onwards
    */
    public static void eatSomeBananas(XmlNodeList subBananaNodeList, int numberOfBananas)
    {
        XmlNodeList bananasToEat = subBananaNodeList.Cast<XmlNode>().Take(numberOfBananas) as XmlNodeList; //Error down-casting - null!
        if (bananasToEat == null)
            Console.WriteLine("Error! Did not work");
        /*else 
            doSomethingHere(bananasToEat); */
        XmlNodeList remainingBananas = subBananaNodeList.Cast<XmlNode>().Skip(numberOfBananas) as XmlNodeList; //Error down-casting - null!
        eatSomeBananas(remainingBananas, numberOfBananas);
    }

我试图将XmlNodeList转换为IEnumerable<XmlNode> (因为前者继承了后者)--我认为这应该是向上的。之后，我不应该把它降回XmlNodeList吗？但如果没有，为什么不呢？

Answer 1

之后，我不应该把它降回XmlNodeList吗？但如果没有，为什么不呢？

不，因为从Skip返回的值不是XmlNodeList。它只被声明为IEnumerable<XmlNode>，我希望Skip实现可能使用迭代器块.当然，如果Skip对XmlNodeList有任何详细的了解，我会感到惊讶的。Take将以完全相同的方式工作。

就我个人而言，我完全避免使用旧的XML，而只是使用LINQ。这对LINQ来说很自然--而且通常是一个更好的XML，IMO。

您不必使用这个，请注意-您可以将整个代码更改为使用IEnumerable<XmlNode>而不是XmlNodeList

public static void eatSomeBananas(IEnumerable<XmlNode> subBananaNodeList, int numberOfBananas)
{
    IEnumerable<XmlNode> bananasToEat = subBananaNodeList.Take(numberOfBananas);
    IEnumerable<XmlNode> remainingBananas = subBananaNodeList.Skip(numberOfBananas);
    // Added condition to avoid infinite recursion
    if (remainingBananas.Any())
    {
        eatSomeBananas(remainingBananas, numberOfBananas);
    }
}

然后，在调用该方法时，只需调用一次Cast：

eatSomeBananas(bananaNodeList.Cast<XmlNode>(), 2);

下面是LINQ版本，我更喜欢这个版本：

using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

public class Test
{
    public static void Main(string[] args)
    {
        XDocument someDoc = XDocument.Parse(
            @"<bananas>
                <banana tasty='yes'></banana>
                <banana tasty='very'></banana>
                <banana tasty='amazing'></banana>
                <banana tasty='mind-blowing'></banana>
                <banana tasty='disgusting'></banana>
              </bananas>");
        IEnumerable<XElement> bananas = someDoc.Descendants("banana");
        EatSomeBananas(bananas, 2);
    }

    public static void EatSomeBananas(IEnumerable<XElement> bananas, int numberOfBananas)
    {
        var bananasToEat = bananas.Take(numberOfBananas);
        Console.WriteLine("Eating some bananas"); 
        foreach (var element in bananasToEat)
        {
            var tasty = element.Attribute("tasty").Value;
            Console.WriteLine($"Tasty: {tasty}");
        }
        Console.WriteLine("Eaten the bananas");
        var remainingBananas = bananas.Skip(numberOfBananas);
        if (remainingBananas.Any())
        {
            EatSomeBananas(remainingBananas, numberOfBananas);
        }
    }
}

请注意，对于生产实现，我会避免递归，并可能周期性地实现结果-否则每次都会迭代，跳过一个负载，然后取一些。

Answer 2

我只是转换成一个IQueryable并使用它，比使用XmlNodeList容易得多。

    public static void Main(string[] args)
    {
        XmlDocument someDoc = new XmlDocument();
        someDoc.LoadXml(@"<bananas>
                        <banana tasty='yes'></banana>
                        <banana tasty='very'></banana>
                        <banana tasty='amazing'></banana>
                        <banana tasty='mind-blowing'></banana>
                        <banana tasty='disgusting'></banana>
                      </bananas>");
        XmlNodeList bananaNodeList = someDoc.SelectNodes("//banana");

        var allBananas = bananaNodeList.Cast<XmlNode>().AsQueryable();

        eatSomeBananas(allBananas, 2);
    }

    public static void eatSomeBananas(IQueryable<XmlNode> subBananas, int numberOfBananas)
    {
        var bananasToEat = subBananas.Take(numberOfBananas);
        var remainingBananas = subBananas.Skip(numberOfBananas);

        Console.WriteLine(string.Format("Bananas to eat: {0}", bananasToEat.Count()));
        Console.WriteLine(string.Format("Remaining bananas: {0}", remainingBananas.Count()));
        if (!bananasToEat.Any())
            Console.WriteLine("Error! Did not work (not enough bananas!)");
        else 
            eatSomeBananas(remainingBananas, numberOfBananas);
    }

输出：

Bananas to eat: 2
Remaining bananas: 3
Bananas to eat: 2
Remaining bananas: 1
Bananas to eat: 1
Remaining bananas: 0
Bananas to eat: 0
Remaining bananas: 0
Error! Did not work (not enough bananas!)