基礎

所述 base 關鍵字用於從基類訪問成員。它通常用於呼叫虛方法的基本實現，或指定應呼叫哪個基本建構函式。

選擇一個建構函式

public class Child : SomeBaseClass {
    public Child() : base("some string for the base class")
    {
    }
}

public class SomeBaseClass {
    public SomeBaseClass()
    {
        // new Child() will not call this constructor, as it does not have a parameter
    }
    public SomeBaseClass(string message)
    {
        // new Child() will use this base constructor because of the specified parameter in Child's constructor
        Console.WriteLine(message);
    }
}

呼叫虛方法的基本實現

public override void SomeVirtualMethod() {
    // Do something, then call base implementation
    base.SomeVirtualMethod();
}

可以使用 base 關鍵字從任何方法呼叫基本實現。這將方法呼叫直接繫結到基本實現，這意味著即使新的子類重寫虛擬方法，仍將呼叫基本實現，因此需要謹慎使用。

public class Parent
{
    public virtual int VirtualMethod()
    {
        return 1;
    }
}

public class Child : Parent
{
    public override int VirtualMethod() {
        return 11;
    }

    public int NormalMethod()
    {
        return base.VirtualMethod();
    }

    public void CallMethods()
    {
        Assert.AreEqual(11, VirtualMethod());

        Assert.AreEqual(1, NormalMethod());
        Assert.AreEqual(1, base.VirtualMethod());
    }
}

public class GrandChild : Child
{
    public override int VirtualMethod()
    {
        return 21;
    }

    public void CallAgain()
    {
        Assert.AreEqual(21, VirtualMethod());
        Assert.AreEqual(11, base.VirtualMethod());

        // Notice that the call to NormalMethod below still returns the value
        // from the extreme base class even though the method has been overridden
        // in the child class.
        Assert.AreEqual(1, NormalMethod());
    }
}