Question

鉴于以下内容。拥有和不拥有虚拟关键字有什么区别？

public class Test
{
    public Test()
    {
        this.UserTests = new List<UserTest>();
    }
    public int TestId { get; set; }
    public virtual ICollection<UserTest> UserTests { get; set; }
}

Answer 1

考虑以下Person和Employee类：

public class Person
{
    public string Name { get; set; }

    public string WhoAmI()
    {
        return "I'm just a person and my name is " + this.Name;
    }
}

public class Employee : Person
{
    public string WhoAmI()
    {
        return "I'm an employed person and my name is " + this.Name;
    }
}

如您所见，WhoAmI方法在任何类中都未标有virtual或override。但是，当您运行以下代码时：

Employee p = new Employee { Name = "John Smith" };
p.WhoAmI(); // yields "I'm an employed person and my name is John Smith"

但是，这段代码：

Person p = new Employee { Name = "John Smith" };
p.WhoAmI(); // yields "I'm just a person and my name is John Smith"

差异的原因很简单。在第一种情况下，您明确指示编译器通过将WhoAmI变量引用为p来调用更具体的Employee，然后将调用Employee.WhoAmI。

在后一种情况下，我们将p称为其基类Person，因此调用了Person.WhoAmI。

的多形性：

如果我们想要p作为Person我们仍然可以调用更具体的实现，那该怎么办？

virtual和override就派上用场了：

public class Person { public string Name { get; set; } public virtual string WhoAmI() { return "I'm just a person and my name is " + this.Name; } } public class Employee : Person { public override string WhoAmI() { return "I'm an employed person and my name is " + this.Name; } }

现在它产生'正确'的结果：

Person p = new Employee { Name = "John Smith" }; p.WhoAmI(); // yields "I'm an employed person and my name is John Smith"

此外，使用多态列表时：

var data = new List<Person>(); data.Add(new Person { Name = "Regular Person" }); data.Add(new Employee { Name = "Employed Person" }); foreach (var p in data) { p.WhoAmI(); // will call the 'correct' method }

Answer 2

这意味着如果其他class来自您的Test基地class，如果需要，它将能够覆盖继承的UserTests private ICollection<UserTest> _userTests; public class ComplexTest : Test { public override ICollection<UserTest> UserTests { get { return _userTests.Where(...)} //class-specific logic set { _userTests = value } } } 1}}属性逻辑与其他逻辑，例如：

{{1}}

标记为“虚拟”的类成员集合与没有“虚拟”关键字的类成员集合之间有什么区别

2 个答案:

的多形性：