Question

我在IndexOf()中使用List<T>方法看到的所有示例都是基本的字符串类型。我想知道的是如何根据一个对象变量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：没有用于C＃2.0的lambdas（原始版本不使用LINQ或任何.NET 3+功能，只是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lambdas：

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

你可以通过覆盖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

对不起，还有一个更好的措施：）

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

我更喜欢这个

    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))];
        }

Answer 6

答案是让那些来这里的人知道为什么IndexOf() 不起作用。

您的类必须覆盖 Equals的{{1}}方法，并具有以下声明。

object

如何使用List <object> </object>的IndexOf（）方法

6 个答案: