Problem with ListViewItemCollection 'Contains' method

[Piotr Szukalski]

Hi!

I have trouble with 'Contains' method in ListViewItemCol lection class - it
seems like it nevers calls 'Equals' method of class inherited from
ListViewItem... I've found that ListViewItem doesn't override 'Equals'
method, but I _DO_ override it in my class. Have a look at thread:

http://groups.google.com/group/microsoft.public.dotnet.framework.windowsforms/browse_frm/thread/690bbcd25e81a140/75351591db8d07c5?lnk=st&q=ListViewItemCollection+contains+equals&rnum=2&hl=pl#75351591db8d07c5

.... and at this piece of code:

using System;
using System.Collecti ons;
using System.Windows. Forms;

namespace CollectionsTest
{
class Class1
{
[STAThread]
static void Main(string[] args)
{
ArrayList ar = new ArrayList();
ar.Add(new MyClass("1"));
ar.Add(new MyClass("2"));

ListView.ListVi ewItemCollectio n col = new ListView.ListVi ewItemCollectio n(new ListView());
col.Add(new MyClass("1"));
col.Add(new MyClass("2"));

System.Console. WriteLine("Cont ains: {0}", ar.Contains(new MyClass("1")));
System.Console. WriteLine("Cont ains: {0}", col.Contains(ne w MyClass("1")));
System.Console. ReadLine();
}
}

class MyClass : System.Windows. Forms.ListViewI tem
{
private string str;

public MyClass(string s)
{
str = s;
}

public override bool Equals(object obj)
{
return str.Equals(obj. ToString());
}

public override int GetHashCode()
{
return str.GetHashCode ();
}

public override string ToString()
{
return str;
}
}
}

ArrayList do calls my 'Equals' method, but ListViewItemsCo llection don't.
Any ideas?

Cheers,
Piotrek

[Jakob Christensen]

RE: Problem with ListViewItemCol lection 'Contains' method

ListViewItemCol lection.Contain s does the equivalent of calling
Object.Referenc eEquals when comparing an item to the items in the list, so it
does not call Object.Equals. This means that ListViewItemCol lection.Contain s
only compares references. You will have to implement your own comparison if
you consider two items with the same data to be equivalent.

HTH, Jakob.
--

http://www.dotninjas.dk

http://www.powerbytes.dk

"Piotr Szukalski" wrote:
[color=blue]
> Hi!
>
> I have trouble with 'Contains' method in ListViewItemCol lection class - it
> seems like it nevers calls 'Equals' method of class inherited from
> ListViewItem... I've found that ListViewItem doesn't override 'Equals'
> method, but I _DO_ override it in my class. Have a look at thread:
> http://groups.google.com/group/micro...351591db8d07c5
>
> .... and at this piece of code:
>
> using System;
> using System.Collecti ons;
> using System.Windows. Forms;
>
> namespace CollectionsTest
> {
> class Class1
> {
> [STAThread]
> static void Main(string[] args)
> {
> ArrayList ar = new ArrayList();
> ar.Add(new MyClass("1"));
> ar.Add(new MyClass("2"));
>
> ListView.ListVi ewItemCollectio n col = new ListView.ListVi ewItemCollectio n(new ListView());
> col.Add(new MyClass("1"));
> col.Add(new MyClass("2"));
>
> System.Console. WriteLine("Cont ains: {0}", ar.Contains(new MyClass("1")));
> System.Console. WriteLine("Cont ains: {0}", col.Contains(ne w MyClass("1")));
> System.Console. ReadLine();
> }
> }
>
> class MyClass : System.Windows. Forms.ListViewI tem
> {
> private string str;
>
> public MyClass(string s)
> {
> str = s;
> }
>
> public override bool Equals(object obj)
> {
> return str.Equals(obj. ToString());
> }
>
> public override int GetHashCode()
> {
> return str.GetHashCode ();
> }
>
> public override string ToString()
> {
> return str;
> }
> }
> }
>
> ArrayList do calls my 'Equals' method, but ListViewItemsCo llection don't.
> Any ideas?
>
> Cheers,
> Piotrek
>
>[/color]

[Piotr Szukalski]

RE: Problem with ListViewItemCol lection 'Contains' method

Hi!
[color=blue]
> ListViewItemCol lection.Contain s does the equivalent of calling
> Object.Referenc eEquals when comparing an item to the items in the list, so it
> does not call Object.Equals. This means that ListViewItemCol lection.Contain s
> only compares references. You will have to implement your own comparison if
> you consider two items with the same data to be equivalent.[/color]

Thanks for your answer. I still consider it strange that one
implementation of IList works one way and another seems to follow other
rules... Well, I'm not M$ to make the law... However I wish to find such
information in docs, because it took a while to find bug in my code.

Many thanks,
Piotrek