Make sure base method gets called in C#

Make sure base method gets called in C#

Can I somehow force a derived class to always call the overridden methods base?

public class BaseClass
{
    public virtual void Update()
    {
        if(condition)
        {
            throw new Exception("..."); // Prevent derived method to be called
        }
    }
}

And then in a derived class :

public override void Update()
{
    base.Update(); // Forced call

    // Do any work
}

I've searched and found a suggestion to use a non-virtual Update() but also a protected virtual UpdateEx(). It just doesn't feel very neat, isn't there any better way?

I hope you get the question and I am sorry for any bad English.

回答1

Use the template method pattern - don't override the base method which needs to do some work, override one specific bit, which can either be abstract or a no-op in the base class. (The decision about whether to make it a no-op or abstract is usually fairly obvious - does the base class make sense on its own, as a concrete class?)

It sounds like this is basically the pattern you've found with UpdateEx - although it's usually UpdateImpl or something similar in my experience. There's nothing wrong with this as a pattern, in my view - it avoids any idea of forcing all derived classes to write the same code to call the base method.

回答2

This took me a bit to get what Update and UpdateEx would look like. Here's a code example that might help others.

public class BaseClass
{
    // This is the Update that class instances will use, it's never overridden by a subclass
    public void Update()
    {
        if(condition);
        // etc... base class code that will always run

        UpdateEx(); // ensure subclass Update() functionality is run
    }

    protected virtual void UpdateEx()
    {
        // does nothing unless sub-class overrides
    }
}

A subclass will never have any implementation for Update(). It'll uses UpdateEx() to add implementation to Update();

public class ConcreteClass : BaseClass
{
    protected override void UpdateEx()
    {
        // implementation to be added to the BaseClass Update();
    }
}

Any instance of ConcreteClass will use the BaseClass implementation of Update() along with however ConcreteClass extends it with UpdateEx().

我遇到的问题是多次继承，

Base

A:Base

B:A

A override method1 of Base

B need add some extra work beyond method1

所以，方法2更适合我，在A里面新加一个virtual方法，然后直接在A里面method1里面，新加的virtual方法