c# - 我想要一个 String 字段由另外两个字段组成

Question

我希望 Fullname 由 FirstName 和 Lastname 组成，但出现以下异常:

A field initializer cannot reference the non static field, method or property 'Employee.FirstName' / 'Employee.LastName'

class Employee
{
    public string FirstName { get; }
    public string LastName { get; }
    private string FullName = string.Format("{0}, {1}", FirstName, LastName);
}

Answer 1

运行时不保证类字段的分配顺序。这就是编译器警告您编译时错误的原因。

如果 FullName 是公共(public)属性(property)，您可以:

class Employee
{
    public string FirstName { get; }
    public string LastName { get; }
    public string FullName => $"{FirstName} {LastName}";
}

对于不使用 C#-6 的人:

class Employee
{
    public string FirstName { get; private set; }
    public string LastName { get; private set; }
    public string FullName 
    {
        get { return string.Format("{0} {1}", FirstName, LastName); } 
    }
}

或者，如果您不希望它公开，则需要通过类构造函数实例化这些字段

class Employee
{
    public Employee(string firstName, string lastName)
    {
        FirstName = firstName;
        LastName = lastName;
        fullName = $"{FirstName} {LastName}";
    }

    public string FirstName { get; }
    public string LastName { get; }
    private string fullName;
}