如何创建类的（多态）集合/列表/数组，其中每个类可能具有一些不同的属性

Question

If i wanted to create a Car Engine Design for a game i will do the following:

The Base class:

public class EngineParts {
        public string name;
        public int ID; 
        public GameObject Mesh; 
        public Vector3 Position; 
        public Quaternion Rotation; 
        public string Description;
        public float new_value; // the brand new price of it
}

Then i would have the classes that inherits from it:

public class Rods : EngineParts
    {    
    }

public class Pistons : EngineParts
    {
        public float Size=51;
        public float Compression=51;
    }

public class Turbo : EngineParts
    {
        public float maxboostpressure;
        public float minboostpressure;
        public float MaxOperatingRPM;
        public float MinOperatingRPM;
        public float AirToEngineRatio;
        public float wasteGatePressure;
    }

The importing thing here is that all car parts share some common values that are in the Base class those values are name, ID, Mesh, Position, Rotation.. etc

They also have other values that are more specific for the part itself, like for instance the Turbo has maxboostpressure which determines the maximum pressure of boost the turbo can handle.

Now in the actual game I need to be able to make the use of the parts as one collection

public EngineParts[] Part = new EngineParts[3];

Part[0] = new Rods();
Part[1] = new Pistons();
Part[2] = new Turbo();

I can therefore loop through all parts when needed since they are all of type EngineParts .

But when trying to assign a value to max maxboostpressure , i am unable to do that.

   //Note: Part[1] here is pistons
    Part[1].name = "SportPiston"; // this will work since it is type of EngineParts
    Part[1].maxboostpressure = 5.0; // this will not work

and that is due to that it is of type EngineParts

I can however say:

Rods rd = new Rods();
Pistons pt = new Pistons();
Turbo tb = new Turbo();

pt.name = 5; // this will work
pt.maxboostpressure = 5; // this will work

Now they do share the same DAta from the Base class, but i cant put the Rods, Pistons, Turbo in one collection to loop through or pass them in a function that works on all of them.

So

Question Here is

How can i best do this?
1- Have all the parts of the engine in one collection/List
2- Be able to have extra data stored on each individual type of part as well with minimum coding.

I have been reading about
Abstract Classes, Overloading, Polymorphism, and INHERITANCE to solve this but still there is something that i must miss understand, so if anyone could point me in the right direction it would be highly appreciated.

Thank you in Advance

Answer 1

Try a cast like this:

Piston p = Part[1] as Piston;

p will be null if Part[1] isn't a Piston.

Then continue with

if(p!=null)
    doSomethingHere;

Answer 2

The best way is to separate your array into parts of subclasses. Using linq

EngineParts[] Part = new EngineParts[3];

Part[0] = new Rods();
Part[1] = new Pistons();
Part[2] = new Turbo();

Rods[] rods = Part.Where(x => x is Rods).Cast<Rods>().ToArray();
Pistons[] position = Part.Where(x => x is Pistons).Cast<Pistons>().ToArray();
Turbo[] turbo = Part.Where(x => x is Turbo).Cast<Turbo>().ToArray();

Turbo[0].name = "SportPiston"; 
Turbo[0].maxboostpressure = 5.0;

You will have 3 seperate arrays with known type. now you can work with them individually.

Notice that indexes are no more like before. So if you dont want this why not already create separate arrays for them? ;)

Answer 3

The question is, how do you know that the 3rd item in the list is a specific sub-class?

You currently know because you are specifically assigning it a location in the array, however you should approach this as at any time, any sub-class could be in any position in the array.

With that in mind you need to check the type of the array item, and then cast it before you can work on it.

if(Part[1] is Turbo)
{
   ((Turbo)Part[1]).maxboostpressure = 5;
}

There are a few ways you can test the type:

typeof takes a type name (which you specify at compile time).

GetType gets the runtime type of an instance.

is returns true if an instance is in the inheritance tree.

Answer 4

You can use "is" and "as" operators.

var list = new List<EngineParts>();

// add some parts to the list here...

foreach(var part in list) {
  if(part is Turbo) {
    (part as Turbo).maxboostpressure = 123;
  }
}

Answer 5

no copies, etc...

var lst = new List<EngineParts>(); //fill it
foreach(var itm in lst.Where(x => x is Piston).Cast<Piston>())
{
    itm.maxboostpressure = 42;
}