OOP Design Question

Question

Hello I just would like to know the best practice for dealing with this situation in OOP specifically C#. This is probably a very easy question for seasoned OOP people and I can think of a couple of ways I could possibly do it but I'm not sure what the best way to go is. So: We have a base class eg 'Vehicle'. This base class defines certain common properties and methods such as: Weight Height RegistrationNumber CalculateAge() etc. There are a number of derived classes that deal with specific types of vehicle such as Truck Pickup Car Bus etc. Subclasses obv have their own properties and methods unique to the specific type of vehicle. Truck for example might have: MaxLoadWeight IsArticulated So my question is.. I want to define a method where I can provide the RegistrationNumber of a Vehicle of unknown type and have an object returned to me which is of the correct sub class. For example I want a Car object returned if the RegistrationNumber I provide belongs to a car and a truck object returned if it belongs to a truck. What is the best way to do this? Perhaps sub-classing isn't event the best approach. Maybe something interface based would be better? Any opinions?? Many Thanks! S

Scott Lysle · Answer

You could drop each item of any type into a collection and set the key to be equal to the registration number and the value side to hold the object itself. You could then search the collection to locate and return a specific object. You could then call GetType to find out what type of object it is. So if you created a SortedList called sl and loaded each newly instanced object into that list you could search it for a specific key using something like this: private object GetObjectTypeByID( int iCaseNumber) { object o = null ; // find the object by its ID and return the // object to the caller foreach ( DictionaryEntry de in sl) { if (( int )de.Key == iRegistrationNumber) o = de.Value; } return o; } Once the object was returned you could process it differently by type using a switch statement. If you just wanted to get the type something like this would give you that (but handle the prospects of getting a null object returned): private void button1_Click( object sender EventArgs e) { // get a copy of the object by its ID object o = GetObjectTypeByID(1); // display the type of object to the user MessageBox .Show(o.GetType().ToString()); }