I need to send different IEnumerables to an Printer object.
This printer object will then do something to them, inside a foreach loop.
class Printer
{
public Printer(IEnumerable list)
{
foreach (var enumerable in list)
{
//DO STUFF
}
}
}
This lets me send any enumerable, such as an List<T> to the printer object.
such as
var list = new List<string> {"myList"};
new Printer(list); //mylist
This works fine.
BUT if I send a Dictionary<T, T> such as:
var dictionary = new Dictionary<int, string> {{1, "mydict"}};
new Printer(dictionary); //[1, mydict]
It'll have a key and a value. What I would want though, would be separate access to the Value property inside the foreach loop. All I DO have access to is the enumerable object, which has no properties I can use.
Now what if the datatype T is an object containing several properties (this goes for both examples). How would I be able to use these properties in my foreach loop?
Do I honestly have to create an overload of the constructor, foreach possible datatype I might send down to it?
Also, all I need to do in the foreach is not dependable to any datatypes - as it won't manipulate everything. I do need ACCESS to all the properties though.
Also, this is just example code, not actually the production-code I use in my application.
Can you change the code of the Printer class? If it accepted something like an IEnumerable<IPrintable> instead of just an IEnumerable it would be easier. With an interface like this:
interface IPrintable
{
void Print();
}
Then all objects that would be sent to the Printer would need to implement that interface. Then you could do:
class Printer
{
public Printer(IEnumerable<IPrintable> list)
{
foreach (var enumerable in list)
{
enumerable.Print();
}
}
}
And if you have a dictionary of printable objects, something like:
var dict = new Dictionary<int,IPrintable>();
You could just pass the values to the function:
var printer = new Printer(dict.Values);
You could modify your method to accept a delegate that returns the data the print method needs. Something like this:
// You will not need this class, if you always want a single string result.
class PrinterData
{
public string Value { get; set; }
// More properties?
}
class Printer
{
public Printer<T>(IEnumerable<T> list, Func<T, PrinterData> func)
{
foreach (T item in list)
{
PrinterData data = func(item);
// Do something with the data.
}
}
}
Usage:
int[] ints = new int[] {1,2,3};
new Printer().Print(ints, x => new PrinterData() { Value = x.ToString() });
var dictionary = new Dictionary<int, string> {{1, "mydict"}};
new Printer().Print(dictionary, x => new PrinterData() { Value = x.Name + " = " + x.Value });
Per Erik Stendahl's answer is very similar.
You have to extract an enumerable with the values you want to pass before you call new Printer(). In the case of the dictionary this is simple: just use dict.Values. A more general case is:
var list = List<MyObject>()...
var printer = new Printer(list.Select(x => x.MyProperty));
If you want to treat different types differently, you probably should make different methods. If you want to treat them the same, you should accept a common interface, and only use the methods defined for the interface.
It would be possible to do
if (list is Dictionary<int, string>) {
// do special case
}
but I shudder at the thought.
You can even check generically:
class Printer<T>
{
public Printer<T>(IEnumerable list)
{
foreach (var enumerable in list)
{
if (list is Dictionary<T, T>) {
//DO STUFF
}
}
}
}
The problem is that a collection, though it is enumerable, can hold different types of objects, as you saw with the difference between the List and the Dictionary.
To get around this without coding for each object type, you'd have to only accept an enumerable collection of a certain type that you define, for example IEnumerable<IMyType>.
If you can't do anything at the callee, it's up to the caller to make sure it passes an IEnumerable that is "valid" for Printer, like passing dictionary.Values instead of dictionary in your example. However if the class is public and will be used by 3rd party users, you're better to add some generic constraint to your IEnumerable, as others stated.
Here is the result:
I used your guys help, so I guess I shouldn't vote my own as the answer.
class Printer
{
public Printer(IEnumerable<IPrintable> list) //Accepts any collection with an object that implements IPrintable interface
{
foreach (var enumerable in list) //iterate through list of objects
{
foreach (var printable in enumerable)//loops through properties in current object
{
//DO STUFF
}
}
}
}
interface IPrintable : IEnumerable { }
class SomeObject : IPrintable
{
public string Property1 { get; set; }
public string Property2 { get; set; }
public interface IEnumerable
{
IEnumerator GetEnumerator(); //Returns a Enumerator
}
public IEnumerator GetEnumerator()
{
yield return Property1;
yield return Property2;
}
}
I'd naturally need to implement custom GetEnumerator() foreach object - no problem though!
Related
I have a dictionary of Lists with types (Weapon, Armour, Potion) that extended from 1 parent (Item), in a child classes GetItemData overrides with different properties
internal abstract class Item
{
protected string name = "Item";
protected int level = GameConstants.MIN_ITEM_LEVEL;
protected string description = "";
protected Types type;
public enum Types
{
armour, potion, weapon
}
public Dictionary<string, dynamic> GetItemData()
{
return new Dictionary<string, dynamic>() {
{ "name", name},
{ "description", description },
{ "type", type }
};
}
}
//dictionary in player class
protected Dictionary<string, object> inventory
= new()
{
{"WEAPON", new List<Weapon>() },
{"AMOUR", new List<Armour>() },
{"POTION", new List<Potion>() }
//All are extended from Item `class Weapon:Item`
};
I need to show some data from each list to user, for this i create a function that takes a itemSelector for dictionary, and Write data from them to console.
But function that i write is not work, its throw
System.InvalidCastException: "Unable to cast object of type 'System.Collections.Generic.List1[Items.Weapon.Weapon]' to type 'System.Collections.Generic.List1[Items.Item]'."
private void ListPlayerItems(string previewText, string itemSelector)
{
Console.WriteLine(previewText);
int itemIndex = 0;
((List<Item>)inventory[itemSelector]).ForEach(item =>
{
Dictionary<string, dynamic> itemData = item.GetItemData();
Console.Write($"{itemIndex}) Название: {itemData["name"]}; Описание:{itemData["description"]}; ");
if (item is Weapon)
{
Console.Write($"Минимальный урон: {itemData["minDamage"]}; Максимальный урон: {itemData["maxDamage"]}\n");
}
itemIndex++;
});
}
The problem is in Type that takes a List<> in implicit operator
((List<Item>)inventory[itemSelector]).ForEach(item =>
As i get it, i need somehow downcast Item to type of picked List, i dont know how to do that, please help me with that, maybe i make it wrong from start and you know better way to do this
C# does not support variance for classes (see this and this), so List<Item> is not List<Weapon> even if Item is base class for Weapon. For this particular use case you can workaround with non-generic IEnumerable, OfType method and ordinary foreach:
foreach(var item in ((IEnumerable)inventory[itemSelector]).OfType<Item>())
{
// ...use item
}
or leverage covariance of IEnumerable<T>:
foreach(var item in ((IEnumerable<Item>)inventory[itemSelector]))
{
// ...use item
}
Also I would recommend to avoid using dynamic and object typed variables or collections whenever it is possible so possibly it is worth to rework your data structures a little bit.
Recently, when handling collections of objects of the same (base-)class,
I´ve recently found myself writing something like this:
class SomeClass {
public bool PropertyA {get; set;}
}
class EncapsulatingClass {
private List<SomeClass> list = new();
private bool propA;
public bool PropertyA {
get { return propA; }
set {
propA = value;
foreach(SomeClass instance in list)
instance.PropertyA = value;
}
}
}
This is of course so I don´t have to use foreach every time I want to set a property for the collection. While this works fine, I feel like this requires a lot of code for something simple and a lot of repitition with each property.
Is there a better solution, like extracting the logic of "apply this for the property of the same name for each object in the list" into a function and just calling that in the setters?
There is the issue of ownership of the property. If you need to enforce synchronization such that setting PropertyA ins the encapsulating class, all the instances in the list also use the same value.
For example
class SomeClass
{
public SomeClass(EncapsulatingClass parent)
{
Parent=parent;
}
public EncapsulatingClass Parent { get; }
public bool PropertyA { get => Parent.PropertyA; }
}
class EncapsulatingClass
{
private List<SomeClass> list = new List<SomeClass>();
private bool propA;
public bool PropertyA
{
get { return propA; }
set
{
propA = value;
}
}
}
Otherwise, you have multiple PropertyA values, one for each instance, and then you have to decide which one is the master value, and what to do if some are different.
I'm wondering what it is you are doing to need this so often. It makes me think there's a flaw in the design of your application you could avoid by restructuring something but it's difficult to say without more information.
For your specific problem I would discard EncapsulatingClass and use the ForEach method on List<T> for a little more concise code:
myList.ForEach(s => s.PropertyA = true);
Alternatively, if you don't always use List<T> you can write your own extension method to work on all IEnumerables:
public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
{
foreach (var t in source)
action(t);
}
// Call it just like previously:
myIEnumerable.ForEach(s => s.PropertyA = true);
Of course, this is still cumbersome if you need to do it a lot. But I suspect if you do, it's probably a flaw in the design.
I might approach this with a custom List class providing a single mass update method.
public class EasyUpdateList<T> : List<T>
{
public void UpdateAll(Action<T> update)
{
if (update == null)
return;
foreach (T item in this)
update(item);
}
}
Now you don't need a specific encapsulating class, you can just create a new EasyUpdateList and update any number of properties across the collection using the UpdateAll method.
EasyUpdateList<MyClass> list = new EasyUpdateList<MyClass>();
list.Add(instance1);
list.Add(instance2);
...
list.UpdateAll(x =>
{
x.Property1 = "Value1";
x.Property2 = "Value2";
});
This still uses a foreach loop but is much more generic and you don't have to change your other classes or write repeated code for each one.
Of course you could also achieve this with an extension method for a List class if you don't want a new class.
public static void UpdateAll<T>(this IList<T> list, Action<T> update)
{
if (update == null)
return;
foreach (T item in list)
update(item);
}
I have a variable of type Dictionary<int, List<MyType>> where MyType is a class with several properties and methods. I am showing only two properties and no methods as they are irrelevant to the question.
class MyType
{
private string property1;
private double property2;
public string Property1
{
get { return property1; }
set { property1 = value; }
}
public double Property2
{
get { return property2; }
set { property2 = value; }
}
I would like to iterate over the dictionary and find all class instances for which a property (say for example Property2) of the class instance has a specific value.
Once I have this, I would like to modify the value of the property and perform additional calculations.
I have been looking how to do this but cannot seem to find anything that helps. I have looked at the .ToLookup() method but I am not sure how to use it in this context. Any help would be appreciated.
You could use two foreach loops and the LINQ .Where extension method:
using System.Linq;
// ...
foreach (KeyValuePair<int, List<MyType>> kv in dict)
{
foreach (MyType t in kv.Value.Where(v => v.Property2 == 2.0))
{
// Use t for further calculations
}
}
If you want a LINQ-less solution, you might use an if statement inside the inner loop:
foreach (KeyValuePair<int, List<MyType>> kv in dict)
{
foreach (MyType t in kv.Value)
{
if (t.Property2 != 2.0) continue;
// Use t for further calculations
}
}
To iterate over a dictionary you use the KeyValuePair<TKey,TValue> class. Since you have a list as your value you need to nest a loop within the iteration of the dictionary. Here's an example assuming myDictionary is of Dictionary<int, List<MyType>>:
foreach(var keypair in myDictionary)
{
foreach(MyClass m in keypair.Value.Where(v => v.Property1.Equals("something"))
{
//do whatever you want here with m being an object in the list of MyClass
}
}
The LINQ Where statement takes a lambda where whenever the lambda would return true, those objects will be part of the list's iteration.
If you just want an IEnumerable<MyClass> from the internal list and you don't care about the keys you can do this:
var iterableMyClass = myDictionary.SelectMany(kv => kv.Value)
.Where(v => v.Property2.Equals("something"));
Now iterableMyClass is a single IEnumerable<MyClass> object that combined all of the lists within the dictionary. This is because SelectMany is used to 'flatten' multiple collections. The Where operation also filters the returned IEnumerable in the same way as it does within the foreach loop in my first example.
Using this single IEnumerable, you can then use a simple foreach(MyClass m in iterableMyClass) to iterate over all of the objects that matched.
EDIT
Per our discussion below if you need to get a count or tell if the IEnumerable contains at least one item you can do either of the following.
To get a count of matches you can just call .Count() on the IEnumerable object, but if you don't actually need the objects at all you can just do this:
var count = myDictionary.SelectMany(kv => kv.Value).Count(v => v.Property2.Equals("something");
To get a boolean determining if there is at least one match, but don't need the objects that matched:
bool atLeastOne = myDictionary.SelectMany(kv => kv.Value).Any(v => v.Property2.Equals("something");
Say I define a variable like this:
var o = new { RBI = 108, Name = "Roberto Alomar" };
I can do something like:
Console.WriteLine("{0}", o);
But if I try:
foreach (var i in o) {
Console.WriteLine("{0}", o[i]);
}
I get an error:
foreach statement cannot operate on variables of type 'AnonymousType#1' because 'AnonymousType#1' does not contain a public definition for 'GetEnumerator'
So how does it work under the hood? I'd think that a method for turning an object into a string would have to loop through all the properties to accomplish the task. Is there some special method that allows this to happen, or am I misunderstanding how this works?
How does it work under the hood? I'd think that a method for turning an object into a string would have to loop through all the properties to accomplish the task.
Your assumption is that the implementation of ToString is shared between all instances of all anonymous types; that, for example, there is some helper that is logically something like you would do in JavaScript:
var s = "";
for (property in this)
s += property + ":" + this[property];
This assumption is wrong; there is no single one-size-fits-all implementation of ToString for anonymous types. Rather, the compiler knows what all the properties of the anonymous method are and so it generates a brand-new custom implementation of ToString for every distinct anonymous type.
In C#, the foreach loop does not do what the for-in loop does in JavaScript. The C# loop enumerates the members of a collection. The JS loop enumerates the properties of an object.
If you want to enumerate the properties of an object in C# you can do that, it just takes a bit more work:
var s = "";
foreach (PropertyInfo propertyInfo in this.GetType().GetProperties())
s += propertyInfo.Name + ":" + propertyInfo.GetValue(this).ToString();
You cannot do that because anonymous types don't implements IEnumerable interface - it's not a collection just one object. You have to explicitly print the values.
Console.WriteLine("{0}", o.RBI);
Console.WriteLine("{0}", o.Name);
But step yourself back. Do you need anonymous type? Define your own custom type.
class MyType // give it more meaningful name
{
public int RBI { get; set;}
public string Name { get; set;}
}
All anonymous objects have the same methods. They can be compared to each other as long as they have the same named fields with the same types, they all have a ToString() implementation that will give the string as you can see. But they don't have an implementation of an enumerator. Why should they? It's not like Javascript in that sense where you can enumerate over the property names/indices/whatever because... it's C#, that's just not how it is. Why would you think any different?
If you wanted something to work similarly, fortunately we have implicitly typed variables and reflection to help us out there.
var obj = new { Foo = "asd", Bar = "add", Gar = "123" };
var adapter = PropertyAdapter.Create(obj);
foreach (var name in adapter)
Console.WriteLine("obj.{0} = {1}", name, adapter[name]);
public static class PropertyAdapter
{
public static PropertyAdapter<T> Create<T>(T obj)
{
return new PropertyAdapter<T>(obj);
}
}
public class PropertyAdapter<T> : IEnumerable<string>
{
private T obj;
public PropertyAdapter(T obj) { this.obj = obj; }
public override string ToString()
{
return obj.ToString();
}
public object this[string name]
{
get
{
return typeof(T).GetProperty(name).GetValue(obj, null);
}
}
public IEnumerator<string> GetEnumerator()
{
return typeof(T)
.GetProperties()
.Select(pi => pi.Name)
.GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
When you do
Console.WriteLine("{0}", o);
What's really happening is a call to Object.ToString(), which is inherited and has a built-in implementation for anonymous types that prints the properties and values.
On the other hand,
foreach (var i in o) { .. }
Can't work, because o must be an IEnumerable (or IEnumerable<>)
EDIT: The equivalent of what your expecting Enumerating over the string that is printed when using WriteLine can be achieved (for explanatory purposes, and otherwise useless) by doing:
foreach (var i in o.ToString()) { .. }
However as Jeff Mercado points out, that is not what you seem to want (it won't iterate over the properties - only over the individual characters of the already-formatted string)
This is a bit difficult to explain. So here it goes.
I have a function like this:
public T FooBar<T>(Func<T> function)
{
T returnData = function();
// want to iterate through returnData to do something to it
return returnData;
}
If the returnData (T) is an IEnumerable list, then I would like to enumerate through returnData to modify its contents using reflection. But I can't seem to be able to do it. When I try to cast returnData to an enumerable type, I get an exception:
Unable to cast object of type
'System.Collections.Generic.List`1[Cars]'
to type
'System.Collections.Generic.List`1[System.Object]'.
I will not know that the return type will be a list of 'cars' for example ahead of time, only at run time. So I have to check using reflection if it is a list, and then try to cast it so that I can enumerate through it.
Unless I am going about it the wrong way. How can I enumerate through returnData if it is of type T?
One approach is to add a type constraint on T, but this is not ideal:
public T FooBar<T>(Func<T> function) where T : IEnumerable
{
// T is not strongly typed for the enumerated item
If you changed your method slightly (w.r.t. T):
public IEnumerable<T> FooBar<T>(Func<IEnumerable<T>> function)
Then you have strong typing on the actual item being enumerated with the added bonus of accepting enumerable objects.
So I noticed from a second read of your question, there is some confusion about what T means for your variable returnData. In the case where FooBar() is passed a List<Car>, T is List<Car>, and really has no association with the generic type specification of the List<> itself. You can think of it as some List<U> where U is some other, unknown type.
At runtime you will have no simple way to get to U as it is hidden, so to speak, inside T. You could use overloading as some of the other answerers recommend, and provide a non-IEnumerable<U> method and one which takes arguments of type Func<IEnumerable<T>>.
Perhaps with some more details about the goal of FooBar<T> we could make some more specific recommendations.
if (returnData is System.Collections.IEnumerable)
{
foreach (object o in (System.Collections.IEnumerable)returnData)
{
// Do something.
}
}
Really, though, why not have an additional overload like this:
public T FooBar<T>(Func<IEnumerable<T>> function)
Have you tried type casting to IEnumerable instead of IEnumerable<T>? With IEnumerable you can still use it in a foreach loop. The variable each item would go in should be of type object i.e.:
foreach(object item in (IEnumerable)T){...}
You should check first to be sure that T implements IEnumerable.
The issue here is IEnumerable and IEnumerable Of T are not the same... but you can check for the difference and account for it in your code. Note that IEnumerable Of T inherits IEnumerable, so you can wrap the check for the generic version inside the non-generic version.
The following worked for me in a small test I wrote - I hope it is sufficient for you to do what you need.
Here is the meat and potatoes:
class FooBarOfT
{
public T FooBar<T>(Func<T> function)
{
T returnData = function();
//Want to iterate through returnData to do something to it.
if (returnData is IEnumerable)
{
// get generic type argument
var returnDataType = returnData.GetType();
if (returnDataType.IsGenericType)
{
// this is a System.Collections.Generic.IEnumerable<T> -- get the generic type argument to loop through it
Type genericArgument = returnDataType.GetGenericArguments()[0];
var genericEnumerator =
typeof(System.Collections.Generic.IEnumerable<>)
.MakeGenericType(genericArgument)
.GetMethod("GetEnumerator")
.Invoke(returnData, null);
IEnumerator enm = genericEnumerator as IEnumerator;
while (enm.MoveNext())
{
var item = enm.Current;
Console.WriteLine(string.Format("Type : {0}", item.GetType().Name));
}
}
else
{
// this is an System.Collections.IEnumerable (not generic)
foreach (var obj in (returnData as IEnumerable))
{
// do something with your object
}
}
}
return returnData;
}
}
I also set up some supporting test classes:
class Foo
{
private string _fooText;
public Foo(string fooText)
{
_fooText = fooText;
}
public string Execute()
{
return string.Format("executed! with {0} !", _fooText);
}
}
class Bar
{
public string BarContent { get; set; }
}
And a small console app to run some tests:
class Program
{
static void Main(string[] args)
{
// tests
Func<string> stringFunc = () =>
"hello!";
Func<List<Foo>> listFooFunc = () =>
new List<Foo>
{
new Foo("Hello!"),
new Foo("World!")
};
Func<IEnumerable> ienumerableFooFunc = () =>
new Hashtable
{
{ "ItemOne", "Foo" },
{ "ItemTwo", "Bar" }
};
var fooBarOfT = new FooBarOfT();
fooBarOfT.FooBar(stringFunc);
fooBarOfT.FooBar(listFooFunc);
fooBarOfT.FooBar(ienumerableFooFunc);
Console.ReadKey();
}
}