Unable to cast Base class (data contract) to derived class

Question

User-758219241 posted

[DataContract] 
public class SearchCriteria 
{ 
[DataMember] 
public string CountryID { get; set; } 
}
[DataContract] 
public class CitySearchCriteria: SearchCriteria 
{ 
[DataMember] 
public string CityID { get; set; } 
}

I am creating an instance of SearchCriteria in my MVC controller action, and trying to convert it into CitySearchCriteria.

SearchCriteria searchCriteria = new SearchCriteria(); 
searchCriteria.CountryID = "1";
CitySearchCriteria citySearchCriteria = searchCriteria as CitySearchCriteria;

The "citySearchCriteria" object after the above statement is showing NULL value. I was expecting it to show both properties, CountryID and CityID with CountryID populated, and CityID blank... but it is setting the object to NULL.

What could be the solution here? Has DataContract to do anything with this?

Answer 1

User-488622176 posted

Logic if you do this:

searchCriteria = new SearchCriteria(); 

You should do

searchCriteria = new CitySearchCriteria(); 

Answer 2

User1124521738 posted

doing the cast you were doing

SearchCriteria searchCriteria = new SearchCriteria(); 
searchCriteria.CountryID = "1";
CitySearchCriteria citySearchCriteria = searchCriteria as CitySearchCriteria;

This is invalid as CitySearchCriteria : SearchCriteria not SearchCriteria : CitySearchCriteria

This properly uses inheritance

CitySearchCriteria citySearchCriteria = new CitySearchCriteria(); 
citySearchCriteria.CountryID = "1";
SearchCriteria searchCriteria = citySearchCriteria as SearchCriteria;