I'm having a issue sorting an arraylist of custom objects by a string field.
This is the code I'm trying to do:
arrRegion.Sort(delegate(Portal.Entidad.Region x, Portal.Entidad.Region y)
{
return x.RegNombre.CompareTo(y.RegNombre);
});
But I'm getting this error:
Argument type 'anonymous method' is not assignable to parameter type 'System.Collection.IComparer'
What am I missing?
Maybe you should use the extension methods provided in System.Linq namespace:
using System.Linq;
//...
// if you might have objects of other types, OfType<> will
// - filter elements that are not of the given type
// - return an enumeration of the elements already cast to the right type
arrRegion.OfType<Portal.Entidad.Region>().OrderBy(r => r.RegNombre);
// if there is only a single type in your ArrayList, use Cast<>
// to return an enumeration of the elements already cast to the right type
arrRegion.Cast<Portal.Entidad.Region>().OrderBy(r => r.RegNombre);
If you have control over the original ArrayList and you can change its type to a typed list like this List<Portal.Entidad.Region>, I would suggest you do it. Then you would not need to cast everything afterward and can sort like this:
var orderedRegions = arrRegion.OrderBy(r => r.RegNombre);
OfType<>() instead of a Cast<>(). I updated my example with comments.
var orderedRegions = arrRegion.OrderByDescending(r => r.RegNombre);This is because the Sort method expects an IComparer implementation which cannot be a delegate. For example:
public class RegionComparer : IComparer
{
public int Compare(object x, object y)
{
// TODO: Error handling, etc...
return ((Region)x).RegNombre.CompareTo(((Region)y).RegNombre);
}
}
and then:
arrRegion.Sort(new RegionComparer());
P.S. Unless you are still stuck on .NET 1.1 don't use ArrayList. Instead use some strongly typed collections.
You need to actually make a class that implements IComparer, and provide that.
This can be done with a private class:
private class RegNombreComparer: IComparer
{
int IComparer.Compare( Object xt, Object yt )
{
Portal.Entidad.Region x = (Portal.Entidad.Region) xt;
Portal.Entidad.Region y = (Portal.Entidad.Region) yt;
return x.RegNombre.CompareTo(y.RegNombre);
}
}
Then, you do:
arrRegion.Sort(new RegNombreComparer());
This is one downside to ArrayList, and why using List<T> (especially with LINQ) can be advantageous. It simplifies this, and lets you specify your ordering inline:
var results = arrRegion.OrderBy(i => i.RegNombre);
You can also use System.Linq;.
arrRegion.OrderBy(x=>x.RegNombre);
