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C#:Convert IList<object> to List<object>

Posted on 2008-10-10
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Last Modified: 2013-12-17
Is there a way I can convert IList<object> to List<object>? I tried explicit conversion but I failed.
IList<object> var1 = .....
((List<object)var1).Find(.....);

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Question by:karakav
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Expert Comment

by:Priest04
ID: 22685380
ILIst<T> coll1 = GetData();
List<T> coll2 = (List<T>)coll1;

or you can do it in single line, when getting data;

List<T> coll2 = GetData() as List<T>; // where GetData returns IList<T>

Goran
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Author Comment

by:karakav
ID: 22685454
Sorry, I made a Mystake in my question. I would like to convert IList<IEntity> to List<Entity>. Please note that it is a collection of interfaces.
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Expert Comment

by:ajolly
ID: 22685489
use var1.ToList<> method.
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Author Comment

by:karakav
ID: 22685518
I can't. I am using C# 2.0.
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Expert Comment

by:ajolly
ID: 22685607
IList<object> var1 = .....;
List<object> var2 = new List<object>(var1);
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Expert Comment

by:Priest04
ID: 22685631
why doesnt it work karakav, what exception is raised? It should work.

You need to provide some info in order to be helped.
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Author Comment

by:karakav
ID: 22685813
Sorry, I thought my question was clear. Let me update again. When I use explicit cast I get an InvalidCastException. When I cast using the cast keyword, i just get a null collection.
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Expert Comment

by:ajolly
ID: 22685829
did it work ?
IList<object> var1 = .....;
List<object> var2 = new List<object>(var1);
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Author Comment

by:karakav
ID: 22685837
Dear ajolly,

You solution doesn't work because I use a collection of interfaces. And frankly speaking, I don't understand why this should not work because it works when I replace the interface with the object that inherit that interface.
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Expert Comment

by:Priest04
ID: 22686331
So, you dont get compilation errors, only runtime exception? And Entity positively implements IEntity?
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Author Comment

by:karakav
ID: 22709170
As I said before, I get an InvalidCastException, which means I get it at runtime.
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Expert Comment

by:Priest04
ID: 22709483
You said it before, but it doesnt makes sence. I have just created a sample that uses IEntity and Entity, just to confirm that it is possible.

So, the answer to your question is: yes, it is possible, and is straightforward, as you can see the code bellow.
interface IEntity
{
    string PropertyA{get;set;}
    string PropertyB {get;set;}
    string MethodA();
}
 
class Entity : IEntity
{
    string _PropertyA;
    string _PropertyB;
 
    public Entity(string propertyA, string propertyB)
    {
        _PropertyA = propertyA;
        _PropertyB = PropertyA;
    }
 
    #region IEntity Members
 
    public string PropertyA
    {
        get
        {
            return _PropertyA;
        }
        set
        {
            _PropertyA = value; ;
        }
    }
 
    public string PropertyB
    {
        get
        {
            return _PropertyB;
        }
        set
        {
            _PropertyB = value;
        }
    }
 
    public string MethodA()
    {
        return PropertyA + " " + PropertyB;
    }
 
    #endregion
 
    public bool PropertyC
    {
        get { return true; }
    }
 
    public void MethodB()
    {
            
    }
}
 
IList<IEntity> list = new List<IEntity>();
 
list.Add((IEntity)(new Entity("a", "b")));
list.Add((IEntity)(new Entity("c", "d")));
list.Add((IEntity)(new Entity("e", "f")));
 
List<Entity> list2 = list as List<Entity>;

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Author Comment

by:karakav
ID: 22718714
Sorry Priest04. I reall am sorry. I just found out that actually the object I have is a IList that has IEntity object inside . I get it from a iBatis query and for a reason I don't know, it has to come out this way. I can't declare IList<IEntity> and then execute the query and I will get a conversion error. But suprisingly I cant loop through the list in the snippet.

My problem still however, how do I convert that IList in a List<Entity>?
IList theList = ...// query from iBatis
foreach(IEntity in theList)
{
//Do processing here.
}

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Accepted Solution

by:
Priest04 earned 500 total points
ID: 22723389
Have you tried this?


IList theList = ...// query from iBatis
List<Entity> list = new List<Entity>();
 
foreach(object obj in theList)
{
    list.Add((Entity)obj);
}

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Author Comment

by:karakav
ID: 22723456
This is actually what I am using but I wanted another approach that doesn't require iterations.
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Expert Comment

by:Priest04
ID: 22724152
:)

try this, altough I dont know how much effective is your approach

List<Entity> list = new List<Entity>((Entity[]) theList.ToArray( typeof(Entity)));
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Expert Comment

by:Priest04
ID: 22724816
Btw, I have assumed that collection theList is of type ArrayList.

ArrayList theList = ...// query from iBatis

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Author Comment

by:karakav
ID: 22728441
What do you mean about  the effectiveness of the approach?
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Expert Comment

by:Priest04
ID: 22729002
I am not familiar with the internal mechanism of the ToArray method, but could be that the code is literating twice, so the performance can drop. Test it to see which one runs faster, and use the faster onr, not the "better looking" one.

btw

>> This is actually what I am using but I wanted another approach that doesn't require iterations.

All methods reqire iterations, its just weather you will do it in the code, or they will provide a method that does an iteration.

And there is no other way to achieve what you want.
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Author Closing Comment

by:karakav
ID: 31504940
For the time being the iteration works fine, so I will stick to that.
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Expert Comment

by:Justice777
ID: 25699158
What you are talking about is Covariance. It is handled in .net 4.0, but unfortunately, 2.0 does not, so iteration from one list to the other is the only means I know of.
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