C# 中的所有子类是否自动继承继承

Question

Something I was just testing with a simple using() statement.

Got 2 classes: Child and Parent

public class Parent : IDisposable
{
    public void Dispose()
    {
       // disposing stuff
    }
}

public class Child : Parent
{
    public void Dispose()
    {
       // disposing stuff
    }
}

Now when I start using Using() statements:

using(Parent = new Parent()){}

Dispose does get called for Parent

using(Child = new Child()){}

Dispose isn't called

Unless I specifically add:

public class Child : Parent, IDisposable

Or am I overlooking something?

Answer 1

I'm assuming your Dispose method is not virtual and you also have a Dispose method in Child . The problem is that when you cast Child to IDisposable (which using does implicitly), then the compiler is binding to the Dispose method in Parent , since that's the type that implements IDisposable . If Dispose were virtual , then at runtime the binder would look for an override of Dispose in the Child class and call that.

public class Parent : IDisposable
{
    public virtual void Dispose()
    {
        Console.WriteLine("In Disposed");
    }
}

public class Child : Parent
{
    public override void Dispose()
    {
        Console.WriteLine("In Child Disposed");
    }
}

Or, if Child implements IDisposable (which seems redundant), then the cast to IDisposable would bind to the Dispose method on Child instead of Parent .

public class Parent : IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("In Disposed");
    }
}

public class Child : Parent, IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("In Child Disposed");
    }
}

Note that in either case you should call the parent's Dispose method from the child Dispose method, whether you are overriding or implementing the interface yourself. That way you ensure that any unmanaged resources held by the parent class get disposed as well.

public override void Dispose()
{
    Console.WriteLine("In Child Disposed");
    base.Dispose();
}