Overridden method in derived class

Question

I have an abstract class with an abstract method and this class is inherited by over 100 other classes where we override this virtual method.
Now there is a slight change in business requirement and we need to do a check before calling the overridden method. I know I can put a check in each of the 100 class but that doesn't seems to be an elegant way where change is required in all derived classes.

Is there a better approach to handle this change?

public abstract class BaseFunction
{
    public abstract Result FunctionCall();
}

public class Function1 : BaseFuction
{
    public override Result FunctionCall()
    {
        //business logic
    }
}

Answer 1

You can add a wrapper method to your base class like FunctionCallWithCheck , that will perform the check, and then call the original abstract method FunctionCall .

In order to customize the check, I put it in a virtual method with a default implementation that you can override (if needed) in derived classes.

Note: You will have to replace all you calls to FunctionCall , with FunctionCallWithCheck (in the code that uses all these classes).
Of course this is a good approach only if there aren't too many places where you call FunctionCall (you didn't supply info about that).

public abstract class BaseFunction
{
    // Default check. You can override it in derived classes if needed.
    public virtual bool Check()
    {
        return true;    // put your conditions here
    }

    public int FunctionCallWithCheck()
    {
        if (Check())
        {
            return FunctionCall();
        }
        return -1;
    }

    protected abstract int FunctionCall();
};

public class Function1 : BaseFunction
{
    protected override int FunctionCall()
    {
        //business logic
        return 1;
    }
};

I replaced the return type to int since you did not supply the defintion for Result . I assume it has some default value in case the conditions for calling FunctionCall were not met (instead of the -1 value that I used for that).

Update:
As @KlausGütter commented, you can make FunctionCall into a protected method (rather than public ), in order to get a compiler error if you accidently called it instead of FunctionCallWithCheck . I updated my code above.
If you'd rather not change it because of the many derived classes, you can also keep it public (but you'll loose the compiler's protection).