I am designing a very simple inventory system for a game. I have run into an obstacle where I have the inventory (an array of a specific type) that would need to accept multiple types of objects. My code:
IWeapon[] inventory = new IWeapon[5];
public void initialiseInventory(IWeapon weapon, IArmour armour)
{
inventory[0] = weapon; // Index 0 always contains the equipped weapon
inventory[1] = armour; // Index 1 always contains the equipped armour
}
I would get an error stating that the array can't convert the armour object to a weapon object (which is the array type). I then thought I might make a superclass (well, interface to be precise) that IWeapon and IArmour would inherit from. But then I run into another error...
IItem[] inventory = new IItem[5];
public void initialiseInventory(IWeapon weapon, IArmour armour)
{
inventory[0] = weapon; // Index 0 always contains the equipped weapon
inventory[1] = armour; // Index 1 always contains the equipped armour
Console.WriteLine("The weapon name is: " + inventory[0].Name) // Problem!
}
Since the array type is IItem, it would only contain properties and methods from IItem, and not from IWeapon or IArmour. Thus the problem came in that I could not access the name of the weapon located in the subclass (subinterface) IWeapon. Is there a way I could redirect it somehow to look for properties in a subinterface (IWeapon or IArmour) rather than the superinterface (IItem)? Am I even on the right path?
Since the first item will always be a weapon, and the second will always be armor, you shouldn't use an array (or any data structure) at all. Just have two separate fields, one that holds a weapon and another an armor instance.
private IWeapon weapon;
private IArmour armor;
public void initialiseInventory(IWeapon weapon, IArmour armour)
{
this.weapon = weapon;
this.armor = armor;
}
This is an interesting (and common) puzzle. You have figured out its first part correctly: in order to store the elements in a single array, the array type must match the common ancestor of all elements that go into the array. Of course, this limits the functionality to only what's offered by that common ancestor, which apparently is not enough in your circumstances.
The second part (namely, what to do with elements once you have them all in the array) is a bit harder. You need either a type cast, or a multiple dispatch. The type cast is easy: just add (IWeapon) in front of the element:
((IWeapon)inventory[0]).Name
For multiple items, you can use LINQ:
foreach (IWeapon w in inventory.OfType<IWeapon>()) {
Console.WriteLine("The weapon name is: " + w.Name);
}
Multiple dispatch is a lot more complex. It lets you make methods virtual with respect to more than one object. In return you must sacrifice the simplicity offered by the language: calling methods would require making special objects, rather than calling methods directly. Take a look at the Visitor Pattern for some ideas of how to deal with multiple dispatch.
You can use the is operator to determine if a variable implements a specific interface and then cast that variable to an instance of that interface.
if (inventory[0] is IWeapon)
{
IWeapon myWeapon = (IWeapon)inventory[0];
Console.WriteLine("The weapon name is: " + myWeapon.Name);
}
In the parent class/ interface, you need to decide what common operations/ attributes are truly meant to go here.
It might be worth having the interface something like this:
Interface IItem
{
string name {get};
string itemType {get};
}
then you can just go
foreach(Iitem anItem in itemArray)
{
Console.WriteLine("The " + anItem.itemType + " is: " + anItem.Name);
}
It's not perfect, and raises questions about your model, but it is just something to think about.
Although I totally agree with the answer Servy gave:
If you really really want to use an array (or a List<IITem> ?) you only need to add the Name property to the IItem interface.
interface IItem
{
string Name {get;set;}
}
I doubt if it will help you on the long run, so I'd go for Servy's answer.
I detect a little confusion between interfaces and classes, but nevertheless, you should very simply make sure that IItem has the Name property on it (which, if its an interface, IWeapon and IArmour would need to implement), rather than putting the Name property on each subclass (no such thing as a "subinterface" :) )
Perhaps you should post the code of your interfaces/classes though....
Both weapons and armour have names, so that's a property that should go in the IItem interface.
Also, what Servy says makes sense, having an array for different kind of items doesn't make much sense as the specific positions always have the same type of item.
If you want to access them as an array, you can create a class that both has an array, and lets you access the equipped items with the specific type:
public class Inventory {
public IWeapon CurrentWeapon { get; }
public IArmour CurrentArmour { get; }
private IItem[] _items = new IItem[8];
public IItem[int idx] {
get {
return
idx == 0 ? CurrentWeapon :
idx == 1 ? CurrentArmour :
idx_items[idx - 2];
}
}
}
I have to add my 2 cents, because i found the question quite well asked and it may be a common problem.
I would go with something like this:
interface IItem
{
//some common properties / methods
}
interface IWEapon : IItem
{
string Name { get; set; } //maybe this should go to IItem? depends on your actual objects, of course
//some other wepaon specific properties / methods
}
interface IArmor : IItem
{
//some properties / methods
}
class Inventory
{
public Inventory(IWEapon startWeapon, IArmor startArmor)
{
CurrentWeapon = startWeapon;
CurrentArmor = startArmor;
//optional:
m_items.Add(startWeapon);
m_items.Add(startArmor);
}
private List<IItem> m_items = new List<IItem>();
IEnumerable<IItem> InventoryItems
{
get { return m_items; }
}
void AddItem(IItem item)
{
m_items.Add(item);
}
IWEapon CurrentWeapon
{
get;
set;
}
IArmor CurrentArmor
{
get;
set;
}
}
Why design a class for the inventory? Because you could add things like a TotalWeight or ItemCount property, etc. way more easily than if you have just an array of IItem.
Assuming you really require an array to store the different inventory items (and not just two separate fields) then it seems you could just use inheritance. I took the liberty of adding different properties to Weapon and Armor to clarify the use cases.
Base Class:
abstract class Item
{
public string Name { get; set; }
}
Derived Types:
class Weapon : Item
{
public int Power { get; set; }
}
class Armor : Item
{
public int Resistance { get; set; }
}
Example usage:
Item[] inventory = new Item[2];
inventory[0] = new Weapon { Name = "Singing Sword", Power = 10 };
inventory[1] = new Armor { Name = "Chainmail Shirt", Resistance = 5 };
// Note below that the Name property is always accessible because it is defined in the base class.
// Traverse only Weapon items
foreach (Weapon weapon in inventory.OfType<Weapon>())
{
Console.WriteLine(weapon.Power);
}
// Traverse only Armor items
foreach (Armor armor in inventory.OfType<Armor>())
{
Console.WriteLine(armor.Resistance);
}
// Travers all items
foreach (Item item in inventory)
{
Console.WriteLine(item.Name);
}
Related
i've a Method which gets a List where T : Item.
How do i access the property from the Subclasses of Item?
private void CreateShopItem<T>(Transform itemTemplate, Transform shopScrollView, List<T> shopItemList)
where T : Item {
shopItemList.Name //this works
shopItemList.power //this is a property from the class cooling and i cant access it
}
Ive 4 subclasses from the base class Item but i can only access the properties from the Class Item
Item Class:
public class Item
{
public int Id;
public string Name;
public double Cost;
public Sprite Sprite;
public bool IsPlaced;
public Vector3 Position;
public Item()
{
Id = 0;
Name = "Default";
Cost = 0;
Sprite = null;
IsPlaced = false;
Position = Vector3.zero;
}
public Item(int id, string name, double cost, Sprite sprite, bool isPlaced, Vector3 position)
{
this.Id = id;
this.Name = name;
this.Cost = cost;
this.Sprite = sprite;
this.IsPlaced = isPlaced;
this.Position = position;
}
}
Sub Class Cooling:
public class Cooling : Item
{
public float power;
public float temp;
public Cooling(int id, string name, double cost, Sprite sprite, bool isPlaced, Vector3 position,
float power, float temp)
{
base.Id = id;
base.Name = name;
base.Cost = cost;
base.Sprite = sprite;
base.IsPlaced = isPlaced;
base.Position = position;
this.power = power;
this.temp = temp;
}
}
What would be a way to access the property of all subclasses from the Base Class?
Normally if a method needs to access a field/property this field would be included in the type that it accepts. While you can cast the item into a derived type, if you have to do it why accept the base type in the first place?
The problem is that if you use ifs or case when you add a new type you need to remember to come back to this piece of code and update it.
BTW. Use properties, not fields. It is the standard way:
public class Item
{
public int Id { get };
What you're asking the code to do doesn't make logical sense. When you use a generic type:
public class Foo<T>
{
public T Value { get; set; }
public void MyMethod()
{
// example code here
}
}
You are saying that you're going to be using a type (T) but you're not really sure yet which type you'll be using. The type will be specified at a later stage. The only assumption made by the compiler is that your T will derive from object.
This is okay, but that also means that you can't actually use this T with any more precision than you can use object. In the above example, you could call this.Value.ToString() because T is definitely an object (and object has the ToString() method), but you cannot call this.Value.Power because T is not known to be of the type Cooling (or a subtype).
You are able to influence what the compiler knows about the specific type that T will be. You've already done so by specifying that T will definitely be some sort of Item (i.e. class or subclass)
public class Foo<T> where T : Item
{
public T Value { get; set; }
public void MyMethod()
{
// example code here
}
}
Because the expectation is now that T is not just an object but also an Item, the compiler allows you to handle your T type with every known property/method of the Item type. You could access things like:
this.Value.Name
this.Value.Cost
this.Value.Sprite
Because these are properties of the Item class which you can definitely expect to see on any subclass of Item, you are allowed to access them when dealing with a T where T : Item generic type parameter.
You're trying to access a specific type's property (Cooling), without having told the compiler that your generic type is definitely going to be a (sub) class of Cooling.
That directly contradicts the core premise of using a generic type, i.e. treating a range of possible types using the same (generic) code. If that generic code were to only work with one specific type (i.e. Cooling), then there'd be no point in trying to make CreateShopItem work for any type that is not Cooling or one of its subtypes.
You need to go back to the drawing board with what it is that you want.
If I can assume that it is correct that CreateShopItem should work for any Item class, then you should inherently be able to write code that is able to handle any Item object without needing to know the specific concrete class being used.
I am very intentionally ignoring upcasting here because it's a bad approach that tries to cover for a bad design. Generic type upcasting is rarely a good idea. It violates OCP (in all but exceedingly rare examples), and would not be a good idea in this particular scenario anyway.
First of all the example that you show for the this one works and this one doesn't should be wrong because the reference that you are using is a List (List for your example) and the both of them will not work unless you get the element that you want to change from that list (with a loop or maybe with LINQ First() etc)
Secondly, If you want to access a field from a subclass while you have a base class object. You need to cast it to that subclass. For example:
class Item{
...
public int Id;
public string Name;
public double Cost;
}
class Cooling : Item {
...
public float power;
}
//Example method to call
private void CreateShopItem<T>(Transform itemTemplate, Transform shopScrollView, List<T> shopItemList)
where T : Item {
var firstItem = shopItemList().First(); // taking the first element just for example
firstItem.Name = "foo"; // this is fine
var coolingItem = (Cooling) firstItem;
coolingItem.power = 1000; // now this is also fine
}
This will fix your current case but I do not recommend to do it because as the subclasses increase this can turn into a big mess of casting disaster between classes.
I recommend to check out boxing/unboxing topic on C# for future use and best practices.
Assuming I have an object of some type, containing an array of some other type:
public class Mammal
{
public Leg[] Legs { get; set; }
}
public class Leg
{
public int Length { get; }
}
If I e.g. receive a Mammal from some GetMammals() call, how would I go about filtering Legs in Mammal based on a predicate, such as height for example?
Mammal.Legs.Where(l => l.Length > 10);
Above would return an IEnumerable<Legs> which I would then have to find a way to stuff back into Mammal, but is there a neat way to perform this action directly on my Mammal object, assuming I would have to use this filteredMammal object for something else later on?
You allready have written the solution yourself. Every linq-method just returns a new collection instead of modifying the existing one.
In order to do so you´d have to set the returned collection to your mammals property:
myMammal.Legs = myMammals.Legs.Where(myPredicate).ToArray();
This assumes you can set the property.
Another opportunitiy is to write a Remove-method:
void Remove(Predicate<Leg> predicate)
{
this.Legs = this.Legs.Where(x => !predicate(x)).ToArray();
}
This still requires a private setter though.
The best approach is to make Legs a List<Leg>. Then you can just call RemoveAll:
myMammal.Legs.RemoveAll(myPredicate);
Currently I'm trying to write a CSV exporter utility for work to help speed up the process of creating work orders for our supervisors. On paper it's quite a simple concept, import the CSV containing our part information and our current production requirements. The columns of the CSV are being split into separate lists. I'm trying to create a button that will allow the user to automatically set the quantity based on the part number.
The way I'm currently thinking about doing this is by grabbing the specific entry on the list's 'spot' (can't think of a better term).
Example:
Dinosaur List
1. T-Rex
2. Triceratops
3. Allosaurus
Diet List
1. Carnivore
2. Herbivore
3. Carnivore
If my user selected Allosaurus, I would want a value returned of 3, and then I would use that to grab the right entry from my second list, in this case, Carnivore.
I'm not sure exactly how I would go about doing this, and any help or direction would be greatly appreciated.
You should really use Object-Oriented programming in this case.
If I were you, I'd declare a class Dinosaur, and make subclasses for each type of dinosaur. In the super class (Dinosaur), put an abstract property of type DinosaurDiet to force subclasses to implement this property. Here's a bit of code to explain what I'm saying:
enum DinosaurDiet //The enumeration for the types of diet
{
Carnivore,
Herbivore
}
abstract class Dinosaur //abstract meaning it can't be instanciated, and only serves as a superclass
{
public abstract DinosaurDiet Diet { get; }
}
class TRex : Dinosaur
{
public override DinosaurDiet Diet { get { return DinosaurDiet.Carnivore; } }
}
class Triceratop : Dinosaur
{
public override DinosaurDiet Diet { get { return DinosaurDiet.Herbivore; } }
}
class Allosaurus : Dinosaur
{
public override DinosaurDiet Diet { get { return DinosaurDiet.Carnivore; } }
}
Once you have all that, you can make a list of them and get them using an index. Here's how:
List<Dinosaur> dinos = new List<Dinosaur>();
dinos.Add(new TRex());
dinos.Add(new Triceratop());
dinos.Add(new Allosaurus());
//Get the 2nd dinosaur from the list (0-based)
int index = 1;
Dinosaur d = dinos[index];
Make sure to test index >= 0 && index < dinos.Count to avoid an exception when trying to get an element at an out-of-bound index.
So let's say I have an interface in my game, IItem. IItem represents an object with a render component, a weight, and an attached "process". The process may be attached by someone using some ability to affect the item. Maybe something like an "enchantment" in an RPG. Let's say I want that attached process to be able to modify the weight of the IItem. However, I only want a process which is a component of the IItem to be able to do so. Objects outside of the IItem need to be able to get the weight though.
Do I implement a Weight property, with just a getter in the interface? Then does the base class implement a "SetWeight" method, which is declared internal to the Item namespace? That still does not really guarantee that only a component owned by the particular IItem can affect it of course, but at least something in the Input namespace cannot directly change the weight of an item. In C I could do something similar to linked lists in the kernel which can get their container, this would give me a way to make sure the weight and the process had the same container object, however, I do not see an easy way to do this in C#. Furthermore, I think it kind of damages the component based design for a component to have to have a reference back to its parent.
This is a general problem I am running in to as I design my interfaces and classes.
Have you considered using a Dictionary, instead of properties? Something like this:
// Item base class
public Dictionary<string, object> Attributes { get; private set; }
public List<Process> Enchantments { get; private set; }
public virtual T Get<T>(string identifier)
{
var att = this.Attributes.FirstOrDefault(att => att.Key == identifier);
if (att == null) throw new MissingAttributeExeption(identifier); // Or perhaps just return default(T)
if ((att.Value is T) == false) throw new InvalidAttributeCastException(identifier, typeof(T));
var value = att.Value;
foreach (var ench in this.Enchantments)
{
ench.Modify(identifier, ref value);
}
return value as T; // Maybe you need to cast value to Object, and then to T, I can't remember.
}
// Process class
public string ValueToModify { get; set }
public virtual void Modify(string identifier, ref object value)
{
if (identifier != this.ValueToModify) return;
// In an inherited class, for example a Weightless-Enchantment: Halfs all weight
var castedVal = value as int
value = castedVal / 2;
// Now this one item weights 50% of normal weight, and the original value is still stored in Item's Attributes dictionary.
}
// Some random class
public void Update()
{
var totalWeight = 0;
foreach (var item in this.itemCollection)
{
int weight = item.Get<int>("Weight");
totalWeight += weight;
}
Console.WriteLine("The player weights: {0}", totalWeight);
}
Obviously this means you can't really hardcode attributes, but... Do you ACTUALLY want to do this, in the long run? I mean once you start adding Intelligence, Agility, Strength, Stamina, Endurance, etc.
I know this doesn't solve your posed question, but I should think it's a pretty decent alternative.
Well, I think I get what you're talking about.
To ensure that your process, e.g. IEnchantment may take an IItem as a dependency(keep it as a member), and have IItem have Update/Set methods that take an IEnchantment, and then you can check that, for example:
public void Update(IEnchantment enchantment)
{
if (enchantment.AttachedItem != this)
throw new Exception("Cannot Update Item!");
/*
* Execute Updating Logics
*/
}
Here's one library I tried designing for my own games, maybe it can help you think about something. It's far from perfect, it's barely anything at all, but I hope it can help in any way.
Here it goes my question:
I intend to create several lists of objects, being each of the objects from the same class.
However, within each of the lists, I would like the different instances of the objects to share a common member I could change from any of these instances.
Of course, each of the lists have its own "static" member.
I hope I had explained myself, I am beginner and I am not sure whether my question has an obvious solution.
Edit:
I am working on an existing code, and I make every step by doing a trial-error approach. I do not know exactly how to explain it better: I have List list1, and List list2. The set of instances within list1 will have members with different values, but I want to have a member in class A which can be modified from any instance within the list1 and to be common to all the instances in list1. Similarly for list2, but with a different "static" member that the one in list1.
I think this will roughly achieve what you are looking to do. There are many ways to change the structure of the code below to achieve different goals but basically what you will need to do is create some sort of custom list that when items are added to it, it attaches itself to those items, and removes itself from them when they are removed.
public class CustomList : IList<IItem>
{
public Object CommonMember { get; set; }
private List<IItem> _internalList = new List<IItem>();
public void Add(IItem item)
{
item.OwnedList = this;
this._internalList.Add(item);
}
public void Remove(IItem item)
{
if(this._internalList.Remove(item))
{ item.OwnedList = null; }
}
... you will need to implment more members
}
public abstract class IItem
{
public Object OwnedListCommonMember
{
get {
if(this.OwnedList != null)
{ return this.OwnedList.CommonMember; }
else { return null; }
}
}
public CustomList OwnedList { get; set; }
}