collection question

[Brett Wesoloski]

I have a collection that I add my objects to. When I go to remove an object
from the collect I get an error {"Cannot remove the specified item because
it was not found in the specified Collection."}
Now I do understand what it is saying but I know the object is in the
collection.

Here is some code.

>? CurrentEPCInfo

{KCC.MPAM.RFID.EPCCollection.EPCInfo}

_EPC: "30540232801ADB0000000006"

_ID: "Kleenex"

_Pic: "C:\\Visual Studio
Projects\\RFID\\KCC.MPAM.RFID.RocketCart\\KCC.MPAM .RFID.RocketCart\\Pics\\KleenexTissue.jpg"

EPC: "30540232801ADB0000000006"

ID: "Kleenex"

PIC: "C:\\Visual Studio
Projects\\RFID\\KCC.MPAM.RFID.RocketCart\\KCC.MPAM .RFID.RocketCart\\Pics\\KleenexTissue.jpg"

? CartEPCs[0]

{KCC.MPAM.RFID.EPCCollection.EPCInfo}

_EPC: "30540232801ADB0000000006"

_ID: "Kleenex"

_Pic: "C:\\Visual Studio
Projects\\RFID\\KCC.MPAM.RFID.RocketCart\\KCC.MPAM .RFID.RocketCart\\Pics\\KleenexTissue.jpg"

EPC: "30540232801ADB0000000006"

ID: "Kleenex"

PIC: "C:\\Visual Studio
Projects\\RFID\\KCC.MPAM.RFID.RocketCart\\KCC.MPAM .RFID.RocketCart\\Pics\\KleenexTissue.jpg"

Now they are the same.
Here is the code I am using.
CurrentEPCInfo.ID = "Kleenex";

CurrentEPCInfo.EPC = "30540232801ADB0000000006";

CurrentEPCInfo.PIC = @"C:\Visual Studio
Projects\RFID\KCC.MPAM.RFID.RocketCart\KCC.MPAM.RF ID.RocketCart\Pics\KleenexTissue.jpg";
CartEPCs.Remove(CurrentEPCInfo);

Now what really confuses me is if I do this

LoadedEPCs.Add(CurrentEPCInfo);

LoadedEPCs.Remove(CurrentEPCInfo);
Add it and then remove it right away it works.

Any idea's?

TIA,
Brett

[Jon Skeet [C# MVP]]

Brett Wesoloski wrote:

I have a collection that I add my objects to. When I go to remove an object
from the collect I get an error {"Cannot remove the specified item because
it was not found in the specified Collection."}
Now I do understand what it is saying but I know the object is in the
collection.

Here is some code.

? CurrentEPCInfo

<snip>

That doesn't look like code. Could you post a short but complete
program that demonstrates the problem? See
http://www.pobox.com/~skeet/csharp/complete.html for more information.

Jon

[n!]

Now what really confuses me is if I do this

>
LoadedEPCs.Add(CurrentEPCInfo);

LoadedEPCs.Remove(CurrentEPCInfo);

Add it and then remove it right away it works.

Have you tried placing a breakpoint on all the places you remove an item
from the collection to make sure you haven't tried to remove it more than
once?

What kind of collection are you using?

n!

[Marc Gravell]

I'm guessing that this is due to the [equality] comparer; the vanilla object
comparer (object.Equals(object)) tests for referential integrity... i.e.
things are equal if the *reference* is equal, i.e. they are exactly the same
instance.

I suspect you have two separate instances with the same data. For this to
work, you should really provide your own equality implementation (override
Equals), and (always hand-in-hand) hash-code.

From your example, I'm guessing that EPC is the key value here, so you could
just (in the comparar) compare the EPC values of the two items; for
GetHashCode(), return EPC.GetHashCode().

In 2.0, you can also implement IEquatable<T>, which prives the type-safe
Equals(T), however this should be in addition to overriding Equals. You
might also want to look at providing suitable == and != operators.

But (very, very important); a conformant Equals implementation *must* go
hand in hand with GetHashCode(); any two instances that "equate" *must*
return the same hash code. The reverse is not necessary. Ideally, the
hash-code would be immutable as well... i.e. if you use "EPC" for both
equality and hashing, then this would be a readonly field.

Marc

[Brett Wesoloski]

Sorry

Here is my code to remove the object, the collection is in VB.NET
Public Sub Remove(ByVal value As EPCInfo)

List.Remove(value)

End Sub

Code to add the object

Public Function Add(ByVal value As EPCInfo) As Integer

Return List.Add(value)

End Function

Then in my C# code I add the items to the collection.

private void button1_Click(object sender, EventArgs e)

{

EPCInfo EPC1 = new EPCInfo();

EPC1.ID = "Kleenex";

EPC1.EPC = "30540232801ADB0000000006";

EPC1.PIC = @"C:\Visual Studio Projects\RFID\KCC.MPAM.RFID.RocketCart\KCC.MPAM.RF ID.RocketCart\Pics\KleenexTissue.jpg";

CartEPCs.Add(EPC1);

EPCInfo EPC2 = new EPCInfo();

EPC2.ID = "Huggies";

EPC2.EPC = "305402328074620000000001";

EPC2.PIC = @"C:\Visual Studio Projects\RFID\KCC.MPAM.RFID.RocketCart\KCC.MPAM.RF ID.RocketCart\Pics\HuggiesDiapers.jpg";

CartEPCs.Add(EPC2);

EPCInfo EPC3 = new EPCInfo();

EPC3.ID = "Cottonelle";

EPC3.EPC = "3054023280A0F20000000002";

EPC3.PIC = @"C:\Visual Studio Projects\RFID\KCC.MPAM.RFID.RocketCart\KCC.MPAM.RF ID.RocketCart\Pics\CottonelleRipples.jpg";

CartEPCs.Add(EPC3);

}

Lastly I try to remove an item from the collection. This is where I get the error.



private void button1_Click(object sender, EventArgs e)

{

EPCInfo CurrentEPCInfo = new EPCInfo();

CurrentEPCInfo.ID = "Huggies";

CurrentEPCInfo.EPC = "305402328074620000000001";

CurrentEPCInfo.PIC = @"C:\Visual Studio Projects\RFID\KCC.MPAM.RFID.RocketCart\KCC.MPAM.RF ID.RocketCart\Pics\HuggiesDiapers.jpg";

CartEPCs.Remove(CurrentEPCInfo);

}

But when I look through the collection of CartEPCs I see the info.

Also if I do an add to the CartEPCs and then a remove it works fine.

Brett

"Jon Skeet [C# MVP]" <sk***@pobox.comwrote in message news:11**********************@i3g2000cwc.googlegro ups.com...

Brett Wesoloski wrote:

>I have a collection that I add my objects to. When I go to remove an object
from the collect I get an error {"Cannot remove the specified item because
it was not found in the specified Collection."}
Now I do understand what it is saying but I know the object is in the
collection.

Here is some code.

>? CurrentEPCInfo

<snip>

That doesn't look like code. Could you post a short but complete
program that demonstrates the problem? See
http://www.pobox.com/~skeet/csharp/complete.html for more information.

Jon

[Brett Wesoloski]

March,

Thanks this helps alot and make a lot of sense.

Brett
"Marc Gravell" <ma**********@gmail.comwrote in message
news:Oy*************@TK2MSFTNGP03.phx.gbl...

I'm guessing that this is due to the [equality] comparer; the vanilla
object comparer (object.Equals(object)) tests for referential integrity...
i.e. things are equal if the *reference* is equal, i.e. they are exactly
the same instance.

I suspect you have two separate instances with the same data. For this to
work, you should really provide your own equality implementation (override
Equals), and (always hand-in-hand) hash-code.

From your example, I'm guessing that EPC is the key value here, so you
could just (in the comparar) compare the EPC values of the two items; for
GetHashCode(), return EPC.GetHashCode().

In 2.0, you can also implement IEquatable<T>, which prives the type-safe
Equals(T), however this should be in addition to overriding Equals. You
might also want to look at providing suitable == and != operators.

But (very, very important); a conformant Equals implementation *must* go
hand in hand with GetHashCode(); any two instances that "equate" *must*
return the same hash code. The reverse is not necessary. Ideally, the
hash-code would be immutable as well... i.e. if you use "EPC" for both
equality and hashing, then this would be a readonly field.

Marc

[Jon Skeet [C# MVP]]

Brett Wesoloski <br*************@kcc.omwrote:

Here is my code to remove the object, the collection is in VB.NET

See http://www.pobox.com/~skeet/csharp/incomplete.html

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too