给定的键在字典错误中不存在

Question

the dictionary "_infoCardFactories" is defined as so:

 Dictionary<string, IInfoCardFactory> _infoCardFactories;

the error "the given key was not present in the dictionary" originates from this line of code:

IInfoCard card = _infoCardFactories[category].CreateNewInfoCard(category); 

here is the interface for the dictionary as well the class it is implemented into.

public interface IInfoCardFactory
    {
        IInfoCard CreateNewInfoCard(string category);
        IInfoCard CreateInfoCard(string initialDetails);
        string[] CategoriesSupported { get; }
        string GetDescription(string category);
    }

public class creditcard : IInfoCardFactory,IInfoCard
    { 
        public IInfoCard CreateNewInfoCard(string category)
        {
           creditcard card = new creditcard();
           return card;
        }

} 

i cannot show all of the code, due the fact this is an assigment however i would be greatful if someone could help me out.

Answer 1

You need to implement a class based on this interface and then define your dictionary to use that implementation. There needs to be an instance.

Answer 2

Instead of IInfoCard card = _infoCardFactories[category].CreateNewInfoCard(category);

Use this:

IInfoCard card;
IInfoCardFactory factory;
if (_infoCardFactories.TryGetValue(category, out factory))
     card = factory.CreateNewInfoCard(category);
else
{
    // when category is not in your dictionary
}