Virtual call in constructor with additional method

Question

I have the issue where I need to call a virtual function in my abstract class' constructor.

internal abstract class Item
{
    protected Item(...)
    {
        ...
        CreateBuyButton(...);
    }

    protected abstract void CreateBuyButton(...);
}

If I have my code like this resharper is notifying me about the problem however if I refactor the call into another method resharper doesn't seem to count this as a problem and I'm not sure if it is a problem or not.

internal abstract class Item
{
     protected Item(...)
    {
        ...
        GetValue(...);
    }

    protected abstract void CreateBuyButton(...);

    private void GetValue(...)
    {
        CreateBuyButton(...);
    }
}

Is this valid ? Will the problem still persist ?

I have a little bit more specific question rather than just the reason why I am getting weird behaviour if I have virtual call in constructor. — dB.Employee, Dec 20 '16 at 00:00

John Wu · Accepted Answer · 2016-12-20T00:12:21.747

Yes, it could still be a problem

When the constructor for your base class runs, the constructor(s) for the derived classes haven't run yet. If the overridden method contains logic that depends on the derived class' state, it could encounter issues, because the state hasn't been initialized yet.

You can avoid the problem by removing the logic from the constructor and using lazy initialization instead, e.g.

abstract class Item
{ 
    private Button _buyButton = null;

    public Item()
    {
        //Do nothing
    }

    public Button BuyButton
    {
        get
        {
            if (_buyButton == null) CreateBuyButton(); //Lazy initialization
            return _buyButton;
        }
    }

    public abstract void CreateBuyButton();
}

If you need to pass some state, you'll have to store it:

abstract class Item
{
    private string _productName; 
    private Button _buyButton = null;

    public Item(string productName)
    {
        _productName = productName;
    }

    public Button BuyButton
    {
        get
        {
            if (_buyButton == null) CreateBuyButton(_productName); //Lazy initialization
            return _buyButton;
        }
    }

    public abstract void CreateBuyButton(string caption);
}

Virtual call in constructor with additional method

1 Answers1

Yes, it could still be a problem