Dynamically creating a new instance of IList's type
Solution 1
Try this:
public static void AddNewElement<T>(IList<T> l, int i, string s)
{
T obj = (T)Activator.CreateInstance(typeof(T), new object[] { i, s });
l.Add(obj);
}
Usage:
IList<Customer> l = new List<Customer>();
l.Add(new Customer(1,"Hi there ..."));
AddNewElement(l, 0, "None");
(EDIT):
Try this then:
public static void AddNewElement2(IList l, int i, string s)
{
if (l == null || l.Count == 0)
throw new ArgumentNullException();
object obj = Activator.CreateInstance(l[0].GetType(), new object[] { i, s });
l.Add(obj);
}
Solution 2
If you can use a parameterless constructor and set the properties afterwards then you can make your method generic, something like:-
void Process<T>(IList<T> list, int x, string y) where T : MyBase, new()
{
T t = new T();
t.X = x;
t.Y = y;
list.Add(t);
}
Where MyBase is the base for your classes which expose the int and string properties. You can use an interface rather than a base class if you want.
Solution 3
You can use the Activator.CreateInstance
method to invoke a constructor for a class via its type name (as a string) or an instance of System.Type
.
Solution 4
I think you should change your design. You can use abstract factory pattern. Using reflection would degrade performance.
Here is code for factory.
public abstract class MyStore {
public abstract string Name { get; }
public abstract void AddItem(int id, string name);
}
You can consider using interface if your abstract class has no code.
Then create Customer store.
public class CustomerStore : MyStore, IEnumerable<Customer> {
List<Customer> list = new List<Customer>();
public override string Name { get { return "Customer Store"; } }
public override void AddItem(int id, string name) {
list.Add(new Customer(id, name));
}
public IEnumerator<Customer> GetEnumerator() {
return list.GetEnumerator();
}
}
Usage
foreach (MyStore store in List<MyStore>)
store.AddItem(0, "None");
If you want to consider type of store, use
switch (store.Name) {
case "Customer Store":
SomeMethod((CustomerStore)store);
break;
default:
throw new WhatEverException();
}
Solution 5
You could use the Type.GetGenericArguments method to return the type argument of the generic type IList<T>. Then invoke the appropriate constructor.
Type T = l.GetType ( ).GetGenericArguments ( ) [ 0 ];
ConstructorInfo ctor = T.GetConstructor (
new Type [ 2 ] { typeof ( int ), typeof ( string ) } );
System.Diagnostics.Debug.Assert ( ctor != null );
object instance = ctor.Invoke (
new object [ 2 ] { 0, "None" } );
user48408
Updated on June 04, 2022Comments
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user48408 almost 2 years
My application is processing IList's. ILists of different user defined types. I'm thinking that i can use reflection to to see what type of object the IList contains and then create a new instance of that type and subsequently add that to the IList itself?
So at any one time I might be processing
IList<Customer> l;
and I'd like to create a new instance of Customer
Customer c = new Customer(0, "None")
and then add that onto the list
l.Add(c);
Obviously doing this dynamically at run-time is the crux of the problem. Hope somebody can give me some pointers. Thanks brendan
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Konrad Rudolph about 15 yearsThis code doesn't work, and there's nothing similar to achieve this effect.
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Adam Ralph about 15 yearsOops, you are correct, have edited the post accordingly. Thanks
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user48408 about 15 yearsThe problem here is that type(s) is/are in a different assembly so i don't believe i can call Activator.CreateInstance
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Konrad Rudolph about 15 yearsAs long as the assembly is properly loaded, this shouldn't be a problem.
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user48408 about 15 yearsThis looks good. In terms of usage. I have an arrayList of IList's which i'm processing in a foreach. So foreach(IList l in arrayOfILists) { Process(l, 0, "None"); } isn't going to compile which being new to generics i don't see why not (?)
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Adam Ralph about 15 yearsSo that means you want to act on a non-generic IList? In your question you said that you want to act on a generic IList<T> giving IList<Customer> as an example.