C# Implementing Abstract factory pattern

Question

Ive ABSTRACT FACTORY pattern in one of my projects: http://www.dofactory.com/Patterns/PatternAbstract.aspx

Code:

public class QuestaoResposta : QuestaoBaseResposta, IQuestao,IQuestionario
{
    public int IDQuestaoResposta { get; set; }
}

public class QuestaoFactory : QuestoesFactory
{
    public override QuestaoBaseResposta CreateQuestao()
    {
        return new QuestaoResposta();
    }
}

public abstract class QuestoesFactory
{
    public abstract QuestaoBaseResposta CreateQuestao();
}

public class QuestaoBaseResposta : IQuestao, IMarcas, IQuestionario
{
    // Constructor where i want to create a concrete instance 
    // of any class that inherits QuestaoBaseResposta using QuestoesFactory 
    // abstract class, and assign it to current instance of
    // QuestaoBaseResposta class
    public QuestaoBaseResposta(QuestoesFactory qf)
    {
        this = qf.CreateQuestao();
    }
}

Problem is that i cant assing a value to current class using "THIS" keyword.

Example:

QuestaoBaseResposta qs = new QuestaoBaseResposta(new QuestaoFactory());

// Here i want the qs intance to be type of QuestaoResposta
// since im passing QuestaoFactory as argument,without cast anything.
qs.IDQuestaoResposta = 0;

What would you suggest to cast the QuestaoBaseResposta class to the inherit type (QuestaoResposta),without cast?

Answer 1

this is readonly. So you cannot assign to it.

Answer 2

No you can't cast without cast. The usefulness of a factory comes from the fact that xyou do not need to know the exact derived class of the returned object. This is different if you donÄt use a factory but instead calling a constructor where you know the exact type.

Why don't you do it this way:

QuestaoBaseResposta qs = new QuestaoFactory().CreateQuestao();