由于您没有显式调用父构造函数作为子类构造函数的一部分，因此插入了对无参数父构造函数的隐式调用.那个构造函数不存在，所以你会得到那个错误.

Since you don't explicitly invoke a parent constructor as part of your child class constructor, there is an implicit call to a parameterless parent constructor inserted. That constructor does not exist, and so you get that error.

要纠正这种情况，您需要添加一个显式调用:

To correct the situation, you need to add an explicit call:

public Child(int i) : base(i)
{
    Console.WriteLine("child");
}

或者，您可以只添加一个无参数的父构造函数:

Or, you can just add a parameterless parent constructor:

protected Parent() { }