I've implemented an interface which all objects that need ordered will
implement.
I'm still having problems.
Here is a break down of my code:
I have an IOrderedChild interface:
public interface IOrderedChild
{
int Index { get; set; }
}
A Question Element that implements IOrderedChild
public class QuestionElement : DBObjectBase, IOrderedChild
{
public int Index { get { return _index; } set { _index = value; } }
}
I have a Set class that I reads as follows:
public class Set<T, U> : IEnumerable where T : IEnumerable, ICollection,
ISet
where U : DBObjectBase, IOrderedChild
{
private List<U> _items;
public Set(T list)
{
_items = new List<U>();
IEnumerator listEnumerator = list.GetEnumerator();
while (listEnumerator.MoveNext())
_items.Add((U)listEnumerator.Current);
}
public Set(T list, bool sort): this(list)
{
ELementComparer comparer = new ELementComparer();
_items.Sort(comparer);
}
}
The comparer looks like this:
public class ELementComparer : IComparer<IOrderedChild>
{
int IComparer<IOrderedChild>.Compare(IOrderedChild x, IOrderedChild y)
{
return (x.Index > y.Index) ? 1 : (x.Index < y.Index) ? -1 : 0;
}
}
This will simply not compile. I get the cannot convert error. I'm going
mad. I really wanted to derive a new class from Set that would have the
extra constraint on U and put the overloaded constructor in the derived
class.
Thanks for helping
Paul
[EMAIL PROTECTED]
From: Ryan Heath <[EMAIL PROTECTED]>
Reply-To: "Discussion of advanced .NET topics."
<ADVANCED-DOTNET@DISCUSS.DEVELOP.COM>
To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
Subject: Re: [ADVANCED-DOTNET] Generics Comiler error/headache
Date: Wed, 25 Jan 2006 15:13:10 +0100
Hi Paul Cowan,
you could also implement an IComparable<> on your QuestionElement class
class QuestionElement : IComparable<QuestionElement>
{
...
int IComparable<QuestionElement>.CompareTo(QuestionElement other)
{
return Comparer<int>.Default.Compare(this.Index, other.Index);
}
}
by then you do not need to specify a Comparer for the items.Sort function
BTW
there is a design flaw in your case: by using ElementComparer you are
saying more or less that U *is* a QuestionElement (or descendant of)
... So why is U a generic parameter?
HTH
// Ryan
On 1/25/06, Paul Cowan <[EMAIL PROTECTED]> wrote:
> U is a parameterized type I am passing into the class.
>
> It still will not compile.
>
> Thanks
>
>
>
> [EMAIL PROTECTED]
>
>
>
>
>
> >From: Paul van Brenk <[EMAIL PROTECTED]>
> >Reply-To: "Discussion of advanced .NET topics."
> ><ADVANCED-DOTNET@DISCUSS.DEVELOP.COM>
> >To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
> >Subject: Re: [ADVANCED-DOTNET] Generics Comiler error/headache
> >Date: Wed, 25 Jan 2006 13:57:23 +0100
> >
> >Your ElementComparar is defined for the specific type QuestionElement,
> >so downcasting it to the more generic type won't work.
> >
> >This code should compile:
> >
> >List<QuestionElement> _items;
> >
> >public Set(T list)
> >{
> >_items = new List<QuestionElement>();
> >//code to load collection
> >ElementComparer comparer = new ElementComparer();
> >_items.Sort(comparer); //WON'T COMPILE
> >}
> >
> >
> >
> >-----Original Message-----
> >From: Discussion of advanced .NET topics.
> >[mailto:[EMAIL PROTECTED] On Behalf Of Paul Cowan
> >Sent: Wednesday, January 25, 2006 13:49
> >To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
> >Subject: [ADVANCED-DOTNET] Generics Comiler error/headache
> >
> >I am trying to do a custom sort on using the following comparer:
> >
> >public class ElementComparer : IComparer<QuestionElement>
> >{
> >public int Compare(QuestionElement x, QuestionElement y)
> >{
> >return (x.Index > y.Index) ? 1 : (x.Index < y.Index) ? -1 :
> >0;
> >}
> >}
> >
> >I have the following code in the constructor of another object:
> >
> >Then in the constructor of another class, I am trying to sort on a
> >List<U> like this:
> >
> >public Set(T list)
> >{
> >_items = new List<U>();
> >//code to load collection
> >ElementComparer comparer = new ElementComparer();
> >_items.Sort(comparer); //WON'T COMPILE
> >}
> >
> >The compiler error is cannot convert ElementComparer to
> >IComparer<U>. What am I doing wrong.
> >
> >Thanks
> >
> >Paul
> >
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