GetType和typeof

Question

Type typeThing = gumballMachine.GetState().GetType();
if (typeThing == typeof(NoQuarterState)) { ... }


IState state;
public IState GetState() {
    return state;
}


public class NoQuarterState : IState { ... }

I'm using a gumballMachine app from Ch10 of Head First Design Patterns. full code here This works.

Problem: typeThing above smells! Is there a better way?

Answer 1

You could use the is operator :

if(gumballMachine.GetState() is NoQuarterState)
{
   //..
}

This of course would result in true for all types that inherit from NoQuarterState as well though. Based on your example this shouldn't be a problem.

The question is why do you have to distinguish by type in the first place? Usually that's a sign that a better design is in order, ie maybe the the strategy pattern or another use of polymorphism could help.

Answer 2

If you can modify the GumballMachine class you could use an enum instead of types:

public enum StateEnum
{
   NoQuarterState,
   SomeOtherState
}

StateEnum GetState { get; }

if(gumballMachine.GetState.Equals(StateEnum.NoQuarterState)) { ... }

Answer 3

You can try

  object typeThing = gumballMachine.GetState();
  //1st way
  if (typeThing is NoQuarterState) {...}
  //Or 2nd way
  if ((typeThing as NoQuarterState)!=null) {...}