保护

protected 关键字标记字段，方法属性和嵌套类，仅在同一个类和派生类中使用：

public class Foo()
{
    protected void SomeFooMethod()
    {
        //do something
    }

    protected class Thing
    {
        private string blah;
        public int N { get; set; }
    }
}

public class Bar() : Foo
{
    private void someBarMethod()
    {
        SomeFooMethod(); // inside derived class
        var thing = new Thing(); // can use nested class
    }
}

public class Baz()
{
    private void someBazMethod()
    {
        var foo = new Foo();
        foo.SomeFooMethod(); //not accessible due to protected modifier
    }
}