C＃将对象强制转换为通用接口时出错

Question

I have the following code. I am unable to cast the object of ISearchProvider to another interface which the class has implemented.

public interface IGenericSearchProcessor<T> where T: ISearchCriteria
{
    Task<ISearchResponse> Search(T criteria);
}

public class GibsonSearchProvider : IGenericSearchProcessor<ISearchCriteria>, IAggregateSearch, ISearchProvider
{

  public async Task<ISearchResponse> Search(ISearchCriteria criteria)
  {
    return new BasicSearchResponse
    {
        AggregateResults = aggregates
    };
  } 
}

public class GenericSearchStrategy<T> : ISearchStrategy<T> where T : ISearchCriteria
{
    public Task<ISearchResponse> Search(ISearchProvider provider, T criteria)
    {
        //exception here when try to cast.      
        var p = (IGenericSearchProcessor<T>)provider;


        //return ((IGenericSearchProcessor<T>)provider).Search(criteria);
    }
}

Answer 1

That cast would only work if:

1. The object passed to your Search method is of a type that implements IGenericSearchProcessor<T> and,
2. IGenericSearchProcessor<T> implements ISearchProvider . Your code shows that IGenericSearchProcessor<T> implements ISearchCriteria , not ISearchProvider .

If you are just going to cast the parameter to IGenericSearchProcessor<T> , then I would suggest just making that the type of the parameter:

public Task<ISearchResponse> Search(IGenericSearchProcessor<T> provider, T criteria) {
    ...
}

Just doing that will likely show where your other code could be going wrong.