C# ASP.NET： 'Object reference not set to an instance of an object.' System.Xml.Linq.XElement.Attri

Question

创建用于获取、更新、删除电影的应用程序

我试图从XML文件中获取电影列表，但每次我在WebService测试仪上尝试获取电影列表时，我都会遇到这个错误

'对象引用未设置为对象的实例。'System.Xml.Linq.XElement.Attribute(…(返回null

我的代码

public class Movie
{
private static string _xmlDataPath = HttpContext.Current.Server.MapPath("~/App_Data/Movies.xml");
public int Id { get; set; }
public string Title { get; set; }
public string Director { get; set; }
public string Synopsis { get; set; }
public Movie(int id, string title, string director, string sypnosis)
{
this.Id = id;
this.Title = title;
this.Director = director;
this.Synopsis = sypnosis;
}
public XElement toXML(XNamespace ns)
{
return new XElement(ns + "Movie",
new XElement(ns + "Id", this.Id),
new XElement(ns + "Title", this.Title),
new XElement(ns + "Director", this.Director),
new XElement(ns + "Sypnosis", this.Synopsis)
);
}
public static List<Movie> GetAllMovies()
{
List<Movie> movieList = new List<Movie>();
//Load XML file using LINQ
XDocument doc = XDocument.Load(_xmlDataPath);
var xmlMoviesList = doc.Root.Elements();
XNamespace ns = doc.Root.GetDefaultNamespace();
//Get each movie element from XML
foreach (var xmlMovies in xmlMoviesList)
{
Movie movie = new Movie(
int.Parse(xmlMovies.Attribute("Id").Value),
xmlMovies.Element(ns + "Title").Value,
xmlMovies.Element(ns + "Director").Value,
xmlMovies.Element(ns + "Sypnosis").Value
);
//Add to the list
movieList.Add(movie);
}
//Return the list
return movieList;
}

Answer 1

如果您能包含示例XML，那就太好了，否则人们不得不猜测。

使用Id作为属性，您的代码可以很好地解析这个XML文件。

<Root>
<Movie Id="1">
<Title>Alien</Title>
<Director>Ridley Scott</Director>
<Sypnosis>In space no one can hear you scream.</Sypnosis>
</Movie>
</Root>

但是，您编写的toXML函数生成了这个XML，它将Id作为节点

<Root>
<Movie>
<Id>1</Id>
<Title>Alien</Title>
<Director>Ridley Scott</Director>
<Sypnosis>In space no one can hear you scream.</Sypnosis>
</Movie>
</Root>

决定Id是一个属性还是一个节点，并相应地调整代码。将new XElement(ns + "Id", this.Id),更改为new XAttribute(ns + "Id", this.Id)，或将xmlMovies.Attribute("Id").Value更改为xmlMovies.Element(ns + "Id").Value

附带说明一下，请查看int.TryParse的文档，并尝试使用它来代替int.Parse。最好确保您首先在要解析的数据中有一个整数