c# - 虚函数

Question

我不太明白 - 我什么时候应该使用虚函数？如果有人能向我解释一下，我会很高兴，谢谢。

Answer 1

虚拟方法是 polymorphism 的关键.标记为虚拟的方法可以在派生类中被覆盖，以改变或特化类的行为。

例子:

class Base
{
    public virtual void SayHello()
    {
        Console.WriteLine("Hello from Base");
    }
}

class Derived : Base
{
    public override void SayHello()
    {
        Console.WriteLine("Hello from Derived");
    }
}

static void Main()
{
    Base x = new Base();
    x.SayHello(); // Prints "Hello from Base"
    x = new Derived();
    x.SayHello(); // Prints "Hello from Derived"
}

请注意，您可以重新声明(而不是重写)一个非虚方法，但在这种情况下它不会参与多态性:

class Base
{
    public void SayHello() // Not virtual
    {
        Console.WriteLine("Hello from Base");
    }
}

class Derived : Base
{
    public new void SayHello() // Hides method from base class
    {
        Console.WriteLine("Hello from Derived");
    }
}

static void Main()
{
    Base x = new Base();
    x.SayHello(); // Prints "Hello from Base"
    x = new Derived();
    x.SayHello(); // Still prints "Hello from Base" because x is declared as Base
    Derived y = new Derived();
    y.SayHello(); // Prints "Hello from Derived" because y is declared as Derived
}