Is it possible in C# to explicitly convert a base class object to one of it's derived classes? Currently thinking I have to create a constructor for my derived classes that accept a base class object as a parameter and copy over the property values. I don't really like this idea, so I'd like to avoid it if possible.
This doesn't seem like it should work (object is instantiated as new base, so memory shouldn't be allocated for extra members of the derived class) but C# seems to allow me to do it:
class BaseClass
{
... some stuff ...
}
class DerivedClass : BaseClass
{
public bool MyDerivedProperty{ get; set; }
}
static void Main(string[] args)
{
BaseClass myBaseObject = new BaseClass();
DerivedClass myDerivedObject = myBaseObject as DerivedClass;
myDerivedObject.MyDerivedProperty = true;
}
This question is related to
c#
inheritance
casting
downcast
I have found one solution to this, not saying it's the best one, but it feels clean to me and doesn't require any major changes to my code. My code looked similar to yours until I realized it didn't work.
My Base Class
public class MyBaseClass
{
public string BaseProperty1 { get; set; }
public string BaseProperty2 { get; set; }
public string BaseProperty3 { get; set; }
public string BaseProperty4 { get; set; }
public string BaseProperty5 { get; set; }
}
My Derived Class
public class MyDerivedClass : MyBaseClass
{
public string DerivedProperty1 { get; set; }
public string DerivedProperty2 { get; set; }
public string DerivedProperty3 { get; set; }
}
Previous method to get a populated base class
public MyBaseClass GetPopulatedBaseClass()
{
var myBaseClass = new MyBaseClass();
myBaseClass.BaseProperty1 = "Something"
myBaseClass.BaseProperty2 = "Something else"
myBaseClass.BaseProperty3 = "Something more"
//etc...
return myBaseClass;
}
Before I was trying this, which gave me a unable to cast error
public MyDerivedClass GetPopulatedDerivedClass()
{
var newDerivedClass = (MyDerivedClass)GetPopulatedBaseClass();
newDerivedClass.UniqueProperty1 = "Some One";
newDerivedClass.UniqueProperty2 = "Some Thing";
newDerivedClass.UniqueProperty3 = "Some Thing Else";
return newDerivedClass;
}
I changed my code as follows bellow and it seems to work and makes more sense now:
Old
public MyBaseClass GetPopulatedBaseClass()
{
var myBaseClass = new MyBaseClass();
myBaseClass.BaseProperty1 = "Something"
myBaseClass.BaseProperty2 = "Something else"
myBaseClass.BaseProperty3 = "Something more"
//etc...
return myBaseClass;
}
New
public void FillBaseClass(MyBaseClass myBaseClass)
{
myBaseClass.BaseProperty1 = "Something"
myBaseClass.BaseProperty2 = "Something else"
myBaseClass.BaseProperty3 = "Something more"
//etc...
}
Old
public MyDerivedClass GetPopulatedDerivedClass()
{
var newDerivedClass = (MyDerivedClass)GetPopulatedBaseClass();
newDerivedClass.UniqueProperty1 = "Some One";
newDerivedClass.UniqueProperty2 = "Some Thing";
newDerivedClass.UniqueProperty3 = "Some Thing Else";
return newDerivedClass;
}
New
public MyDerivedClass GetPopulatedDerivedClass()
{
var newDerivedClass = new MyDerivedClass();
FillBaseClass(newDerivedClass);
newDerivedClass.UniqueProperty1 = "Some One";
newDerivedClass.UniqueProperty2 = "Some Thing";
newDerivedClass.UniqueProperty3 = "Some Thing Else";
return newDerivedClass;
}
No, there is no built in conversion for this. You'll need to create a constructor, like you mentioned, or some other conversion method.
Also, since BaseClass is not a DerivedClass, myDerivedObject will be null, andd the last line above will throw a null ref exception.
No it is not possible. The only way that is possible is
static void Main(string[] args)
{
BaseClass myBaseObject = new DerivedClass();
DerivedClass myDerivedObject = myBaseObject as DerivedClass;
myDerivedObject.MyDerivedProperty = true;
}
You can implement the conversion yourself, but I would not recommend that. Take a look at the Decorator Pattern if you want to do this in order to extend the functionality of an existing object.
That's not possible. but you can use an Object Mapper like AutoMapper
Example:
class A
{
public int IntProp { get; set; }
}
class B
{
public int IntProp { get; set; }
public string StrProp { get; set; }
}
In global.asax or application startup:
AutoMapper.Mapper.CreateMap<A, B>();
Usage:
var b = AutoMapper.Mapper.Map<B>(a);
It's easily configurable via a fluent API.
Source: Stackoverflow.com