How can I intercept when an item is added or removed from a List<ofType>?

[daokfella]

I have a business object that exposes a collection of other objects
via a List<of Type>. How can I intercept when an item is either added
or removed from this list. Is it possible?

private List<Permission _Permissions;

public List<Permission 2Permissions
{
get
{
if (_Permissions == null)
{
_Permissions = new List<Permission >();
}
return _Permissions;
}
}

The consumer of this can now say
myobject.Permis sions.Add(newPe rmission). I'd like to be able to run
some code when this happens. What's the best way?

Thanks,

Jason

[=?ISO-8859-1?Q?Arne_Vajh=F8j?=]

daokfella wrote:

I have a business object that exposes a collection of other objects
via a List<of Type>. How can I intercept when an item is either added
or removed from this list. Is it possible?

private List<Permission _Permissions;

public List<Permission 2Permissions
{
get
{
if (_Permissions == null)
{
_Permissions = new List<Permission >();
}
return _Permissions;
}
}

The consumer of this can now say
myobject.Permis sions.Add(newPe rmission). I'd like to be able to run
some code when this happens. What's the best way?

The obvious solution would be not to expose the entire list
as a property but instead expose add and remove methods that
modified the list and did whatever you want them do.

Arne

[daokfella]

Yes, I thought of that originally, but consumers of the object need to
have access to the list. I'm thinking of just creating a custom class
that inherits from IList that will raise events during add and remove.

[parez]

On May 7, 10:03 pm, daokfella <jjbut...@hotma il.comwrote:

Yes, I thought of that originally, but consumers of the object need to
have access to the list. I'm thinking of just creating a custom class
that inherits from IList that will raise events during add and remove.

i think you can use the collection class..

http://dotnetcorner.weblog.com/2008/...ollection.html

[Peter Duniho]

On Wed, 07 May 2008 16:12:56 -0700, daokfella <jj******@hotma il.comwrote:

I have a business object that exposes a collection of other objects
via a List<of Type>. How can I intercept when an item is either added
or removed from this list. Is it possible?

You can use BindingList<Tin stead of List<T>. That class has a
ListChanged event that notifies you of changes to the list.

Pete

[Marcin Hoppe]

daokfella pisze:

Yes, I thought of that originally, but consumers of the object need to
have access to the list.

Why exactly do they need the list for? If it is sequential access, you
can expose IEnumerable member. If it is some kind of index lookup, you
can expose proper method that takes an index and returns proper item.

Best regards!
--
Marcin Hoppe
Email: ma**********@gm ail.com
Blog: http://devlicio.us/blogs/marcin_hoppe

[Ignacio Machin ( .NET/ C# MVP )]

On May 7, 7:12*pm, daokfella <jjbut...@hotma il.comwrote:

I have a business object that exposes a collection of other objects
via a List<of Type>. How can I intercept when an item is either added
or removed from this list. Is it possible?

private List<Permission _Permissions;

public List<Permission 2Permissions
{
* *get
* *{
* * * if (_Permissions == null)
* * * {
* * * * *_Permissions = new List<Permission >();
* * * }
* * * return _Permissions;
* *}

}

The consumer of this can now say
myobject.Permis sions.Add(newPe rmission). I'd like to be able to run
some code when this happens. What's the best way?

Thanks,

Jason

Hi,

List<Tdoes not expose this feature, as a matter of fact in code
analysis you have a role because of this.

Take a look at this post: http://blogs.msdn.com/fxcop/archive/...27/585476.aspx

[Daniel Cigic]

Take look at System.Collecti ons.ObjectModel .ObservableColl ection<T>, it
might be what you need.

"daokfella" <jj******@hotma il.comwrote in message
news:e0******** *************** ***********@a23 g2000hsc.google groups.com...

I have a business object that exposes a collection of other objects
via a List<of Type>. How can I intercept when an item is either added
or removed from this list. Is it possible?

private List<Permission _Permissions;

public List<Permission 2Permissions
{
get
{
if (_Permissions == null)
{
_Permissions = new List<Permission >();
}
return _Permissions;
}
}

The consumer of this can now say
myobject.Permis sions.Add(newPe rmission). I'd like to be able to run
some code when this happens. What's the best way?

Thanks,

Jason