如何使用List的IndexOf()方法

Question

我看到的在 List 中使用 IndexOf() 方法的所有示例都是基本字符串类型。我想知道的是如何根据对象变量之一返回作为对象的列表类型的索引。

List<Employee> employeeList = new List<Employee>();
employeeList.Add(new Employee("First","Last",45.00));

我想找到 employeeList.LastName == "Something" 的索引

Answer 1

int index = employeeList.FindIndex(employee => employee.LastName.Equals(somename, StringComparison.Ordinal));

编辑：没有 C# 2.0 的 lambda（原始版本不使用 LINQ 或任何 .NET 3+ 功能，仅使用 C# 3.0 中的 lambda 语法）：

int index = employeeList.FindIndex(
    delegate(Employee employee)
    {
        return employee.LastName.Equals(somename, StringComparison.Ordinal);
    });

Answer 2

public int FindIndex(Predicate<T> match);

使用 lambda：

employeeList.FindIndex(r => r.LastName.Equals("Something"));

注意：

// Returns:
//     The zero-based index of the first occurrence of an element
//     that matches the conditions defined by match, if found; 
//     otherwise, –1.

Answer 3

您可以通过覆盖 Equals 方法来做到这一点

class Employee
    {
        string _name;
        string _last;
        double _val;
        public Employee(string name, string last, double  val)
        {
            _name = name;
            _last = last;
            _val = val;
        }
        public override bool Equals(object obj)
        {
            Employee e = obj as Employee;
            return e._name == _name;
        }
    }

Answer 4

抱歉，还有一个很好的措施:)

int index = employees.FindIndex(
      delegate(Employee employee)
        {
           return employee.LastName == "Something";
        });

编辑： - .NET 2.0 项目中的完整示例。

class Program
{
    class Employee { public string LastName { get; set; } }
    static void Main(string[] args)
    {
        List<Employee> employeeList = new List<Employee>();
        employeeList.Add(new Employee(){LastName="Something"});
        employeeList.Add(new Employee(){LastName="Something Else"});
        int index = employeeList.FindIndex(delegate(Employee employee) 
                           { return employee.LastName.Equals("Something"); });
        Console.WriteLine("Index:{0}", index);
        Console.ReadKey();
    }
}

Answer 5

答案是让那些来这里的人知道为什么IndexOf()
不起作用。

您的类必须重写具有以下声明的对象的Equals方法。

public override bool Equals(object obj)

Answer 6

我更喜欢这样

    private List<Person> persons = List<Person>();

            public PersonService()
            {
                persons = new List<Person>() { 
                    new Person { Id = 1, DOB = DateTime.Today, FirstName = "Pawan", LastName = "Shakya" },
                    new Person { Id = 2, DOB = DateTime.Today, FirstName = "Bibek", LastName = "Pandey" },
                    new Person { Id = 3, DOB = DateTime.Today, FirstName = "Shrestha", LastName = "Prami" },
                    new Person { Id = 4, DOB = DateTime.Today, FirstName = "Monika", LastName = "Pandey" },
                };
            }

public PersonRepository.Interface.Person GetPerson(string lastName)
        {
            return persons[persons.FindIndex(p=>p.LastName.Equals(lastName, StringComparison.OrdinalIgnoreCase))];
        }