Question

这是我的C＃代码。

public class Person
{
    public List<Employee> empDetails;        
}


public class Employee
{
   public string Id { get; set; }
   public string Name { get; set; }
   public string proj { get; set; }
   public string No { get; set; }
}
//This method is defined in a service
    public void ReadFiles()
    {
        DirectoryInfo dir = new DirectoryInfo("E:/NewFolder/NewFiles");
        FileInfo[] files = dir.GetFiles("*.*");
        Person p = new Person();
        Employee e = new Employee();
        foreach (FileInfo f in files)
        {
            XmlDocument doc = new XmlDocument();
            doc.Load(f.FullName);
            e.empId = doc.GetElementsByTagName("Id")[0].InnerText;
            e.empName = doc.GetElementsByTagName("Name")[0].InnerText;
            e.empSeatNo = doc.GetElementsByTagName("No")[0].InnerText;
            e.projGroup = doc.GetElementsByTagName("Grp")[0].InnerText;               
            p.empDetails.Add(e); //Here I get the error "Object reference not set to an instance of an object"
        }          
        }

任何帮助表示赞赏。

Answer 1

Person类不会初始化empDetails。大多数人都会在构造函数中执行此操作。

public class Person
{
   public Person()
   {
       empDetails = new List<Employee>();
   }

  public List<Employee> empDetails { get; private set; }
}

此外，您对属性名称的情况也不符合惯例。 Normaly它会EmpDetails甚至更好的EmployeeDetails。

Answer 2

永远不会分配列表;这应该有效：

public class Person
{
    private readonly List<Employee> empDetails = new List<Employee>();
    public List<Employee> EmploymentDetails { get { return empDetails; } }
}

（并访问.EmploymentDetails，即p.EmploymentDetails.Add(e);）

获取错误：对象引用未设置为对象的实例

2 个答案: