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C# Return an object with an event

I try to return an object in my event:
public class MyEvent : EventArgs
{
public Channels number = new Channels(); // Channels is a class where i declared only variables( i try to return all variables inside this class)
public MyEvent(Channels numero)
{
return numero;
}
}
This code doesn't work and i don't know how to return an object which contains my variables of Channels.

Change that to:
public class MyEvent : EventArgs
{
public Channels Number {get;}
public MyEvent(Channels numero)
{
Number = numero;
//return numero; You cannot use "return" in a CTOR!
}
}
Then you can use it in an EventHandler like this:
void MyEventHandler( object sender, MyEvent e )
{
// sender => object that raised the event
// e => an instance of `MyEvent`, having a property, we can read.
var channels = e.Number; // use the info
}
Of course you would have registered it, before it will be triggered:
someInstanceProvidingTheEvent.MyEventHappened += MyEventHandler;
Raising the event works something like this:
// assume we are in the class that offers the Event
public event EventHandler<MyEvent> MyEventHappened;
protected virtual void OnMyEventHappened( Channels chans )
{
// You may want to add some error fortification, here
MyEventHappened?.Invoke(this, new MyEvent(chans));
}
// raise it
public void SomeMethod(){
var theChannels = new Channels();
// yadda yadda
// now it happens!
OnMyEventHappened(theChannels);
}

public class MyEvent : EventArgs
{
public Channels _channels { get; set; }
public MyEvent(Channels numero)
{
_channels = numero;
}
}
public class Program
{
public Main()
{
Channels myChannels = new Channels();
MyEvent _myEvent = new MyEvent(myChannels);
var youWant = _myEvent._channels;
}
}

ISet<T> that notifies on add and remove?

I'd like an ISet<T> with two additional events ItemAdded and ItemRemoved.
One option I considered was deriving MyHashSet<T> from HashSet<T> but since Add and Remove are not virtual, it would require the use of new. Maybe this is a valid use of the keyword?
Another option I thought would be to implement ISet<T> and delegate everything to a private instance of HashSet<T>. This feels like a bulky solution.
Is there a pattern or framework class that gets me the same result but doesn't require less than elegant/ideal coding?

Based on the comments I received (thanks) here's what I've got:
public class NotifyingHashSet<T>
{
private HashSet<T> hashSet = new HashSet<T>();
public bool Add(T item)
{
bool added = hashSet.Add(item);
if(added && ItemAdded != null)
{
ItemAdded(this, new NotifyingHashSetEvent<T>(item));
}
return added;
}
public bool Remove(T item)
{
bool removed = hashSet.Remove(item);
if(removed && ItemRemoved != null)
{
ItemRemoved(this, new NotifyingHashSetEvent<T>(item));
}
return removed;
}
public event EventHandler<NotifyingHashSetEvent<T>> ItemAdded;
public event EventHandler<NotifyingHashSetEvent<T>> ItemRemoved;
}
public class NotifyingHashSetEvent<T> : EventArgs
{
public NotifyingHashSetEvent(T item)
{
Item = item;
}
public T Item { get; set; }
}

I would recommend inheriting rather than composing in this case.
This will ensure that you get all that HashSet offers like:
Other collection methods such as Contains and other Set operations such as IsSubsetOf
Collection initializers
You could assign it to base type, HashSet<int> foo = new NotifyingHashSet<int>()
My implementation looks like this:
public class NotifyingHashSet<T> : HashSet<T>
{
public new void Add(T item)
{
OnItemAdded(new NotifyHashSetChanged<T>(item));
base.Add(item);
}
public new void Remove(T item)
{
OnItemRemoved(new NotifyHashSetChanged<T>(item));
base.Remove(item);
}
public event EventHandler<NotifyHashSetChanged<T>> ItemAdded;
public event EventHandler<NotifyHashSetChanged<T>> ItemRemoved;
protected virtual void OnItemRemoved(NotifyHashSetChanged<T> e)
{
if (ItemRemoved != null) ItemRemoved(this, e);
}
protected virtual void OnItemAdded(NotifyHashSetChanged<T> e)
{
if (ItemAdded != null) ItemAdded(this, e);
}
}
public class NotifyHashSetChanged<T> : EventArgs
{
private readonly T _item;
public NotifyHashSetChanged(T item)
{
_item = item;
}
public T ChangedItem
{
get { return _item; }
}
}
Some tests to check stuff:
[TestClass]
public class NotifyingHashSetTests
{
[TestMethod]
public void ShouldAddToNotifyingHashSet()
{
var notifyingHashSet = new NotifyingHashSet<int>();
notifyingHashSet.ItemAdded += (sender, changed) => Assert.AreEqual(changed.ChangedItem, 1);
notifyingHashSet.Add(1);
}
[TestMethod]
public void ShouldRemoveFromNotifyingHashSet()
{
//can use collection initializer
var notifyingHashSet = new NotifyingHashSet<int> { 1 };
notifyingHashSet.ItemRemoved += (sender, changed) => Assert.AreEqual(changed.ChangedItem, 1);
notifyingHashSet.Remove(1);
}
[TestMethod]
public void ShouldContainValueInNotifyingHashSet()
{
//can use collection initializer
var notifyingHashSet = new NotifyingHashSet<int> { 1 };
Assert.IsTrue(notifyingHashSet.Contains(1));
}
[TestMethod]
public void ShouldAssignToHashSet()
{
HashSet<int> notifyingHashSet = new NotifyingHashSet<int> { 1 };
Assert.IsTrue(notifyingHashSet.IsSubsetOf(new List<int>{ 1,2 }));
}
}

Your own answer demonstrates how you can wrap a HashSet<T> and Srikanth's answer demonstrates how you can derive from HashSet<T>. However, when you derive from HashSet<T> you have to make sure the new class also correctly implements the Add and Remove methods of the ICollection<T> interface. So I have modified Srikanth's answer to properly create an ISet<T> implementation with notifications that derives from HashSet<T> by using explicit interface implementation of the relevant methods of ICollection<T>:
public class NotifyingHashSet<T> : HashSet<T>, ICollection<T> {
new public void Add(T item) {
((ICollection<T>) this).Add(item);
}
new public Boolean Remove(T item) {
return ((ICollection<T>) this).Remove(item);
}
void ICollection<T>.Add(T item) {
var added = base.Add(item);
if (added)
OnItemAdded(new NotifyHashSetEventArgs<T>(item));
}
Boolean ICollection<T>.Remove(T item) {
var removed = base.Remove(item);
if (removed)
OnItemRemoved(new NotifyHashSetEventArgs<T>(item));
return removed;
}
public event EventHandler<NotifyHashSetEventArgs<T>> ItemAdded;
public event EventHandler<NotifyHashSetEventArgs<T>> ItemRemoved;
protected virtual void OnItemRemoved(NotifyHashSetEventArgs<T> e) {
var handler = ItemRemoved;
if (handler != null)
ItemRemoved(this, e);
}
protected virtual void OnItemAdded(NotifyHashSetEventArgs<T> e) {
var handler = ItemAdded;
if (handler != null)
ItemAdded(this, e);
}
}
public class NotifyHashSetEventArgs<T> : EventArgs {
public NotifyHashSetEventArgs(T item) {
Item = item;
}
public T Item { get; private set; }
}
This class also behaves the same way as your class by only firing events when an element actually is added or removed from the set. E.g., adding the same element twice in succession will only fire one event.

I can't register event CollectionChanged of ObservableCollection

I try to run some code when collection is changed. I keep collection as property in Data class:
public static ObservableCollection<OfferedConfiguration> DeviceAdjustedConfigurations
{
get { return deviceAdjustedConfigurations; }
set { deviceAdjustedConfigurations = value; }
}
and register it in code like that:
Data.DeviceAdjustedConfigurations.CollectionChanged += new NotifyCollectionChangedEventHandler(DeviceAdjustedConfigurationsCollectionChanged);
But after registration CollectionChanged is null and the appropriate code in delegated method is not run. In this place DeviceAdjustedConiguration already contains some data. What am I doing wrong?

You should avoid having a set property accessor for collection types, one reason being the one you experienced here with events. Another problem is if someone caches the collection and adds items to it later.
var old = obj.DeviceAdjustedConfigurations;
obj.DeviceAdjustedConfigurations = new ObservableCollection<OfferedConfiguration>();
old.Add(new OfferedConfiguration()); // what should happen here?
instead, remove the set-accessor and use the existing collection directly.
obj.DeviceAdjustedConfigurations.Add(new OfferedConfiguration());
If you really need to set the collection, you need to handle this with for instance a property change event from the class that owns the DeviceAdjustedConfigurations.
public class Item
{
public static ObservableCollection<OfferedConfiguration> DeviceAdjustedConfigurations
{
get { return deviceAdjustedConfigurations; }
set
{
if (deviceAdjustedConfigurations != value)
{
onDeviceConfigurationsChanging(deviceAdjustedConfigurations, value);
deviceAdjustedConfigurations = value;
}
}
}
public static event EventHandler<ConfigurationChangedEventArgs> DeviceConfigurationsChanging;
private static void onDeviceConfigurationsChanging(
ObservableCollection<OfferedConfiguration> oldList,
ObservableCollection<OfferedConfiguration> newList)
{
var handler = DeviceConfigurationsChanging;
if (handler != null)
{
handler(null, new ConfigurationChangedEventArgs(oldList, newList));
}
}
}
public class ConfigurationChangedEventArgs : EventArgs
{
public ConfigurationChangedEventArgs(
ObservableCollection<OfferedConfiguration> oldList,
ObservableCollection<OfferedConfiguration> newList)
{
OldList = oldList;
NewList = newList;
}
public ObservableCollection<OfferedConfiguration> OldList { get; private set; }
public ObservableCollection<OfferedConfiguration> NewList { get; private set; }
}
public class Consumer
{
public void foo()
{
Item.DeviceConfigurationsChanging += updateEvents;
}
private void updateEvents(object sender, ConfigurationChangedEventArgs args)
{
args.OldList.CollectionChanged -= onCollectionChanged;
args.NewList.CollectionChanged += onCollectionChanged;
}
private void onCollectionChanged(object sender, NotifyCollectionChangedEventArgs args) { }
}

Raise an event via reflection

well ive read a lot of posts here and there about why it isnt reliable to raise events via reflection.. my problem is this.. im using PostSharp to define an interface which allows a class to notify before and after a property is changed..
the NotifyAttribute ive created needs to be able to raise the PropertyBeforeChange and PropertAfterChange events.. thing is, even though i can retrieve the event, its GetRaiseMethod() returns null and hence i cannot raise the said events.. how can i go about doing that?
using PostSharp.Aspects;
namespace Core
{
public delegate void PropertyBeforeChangeEventHandler(object sender, string sPropertyName, object oCurrentValue, ref object oProposedValue, ref bool bCancel);
public delegate void PropertyAfterChangeEventHandler(object sender, string sPropertyName, object oOldValue, object oNewValue);
public interface INotify
{
event PropertyBeforeChangeEventHandler PropertBeforeChange;
event PropertyAfterChangeEventHandler PropertyAfterChange;
}
[Serializable]
public sealed class NotifyAttribute : LocationInterceptionAspect, IInstanceScopedAspect
{
bool _NotifyBefore { get; set; }
bool _NotifyAfter { get; set; }
public NotifyAttribute() { _NotifyAfter = true; }
public NotifyAttribute(bool bNotifyBefore, bool bNotifyAfter) { _NotifyBefore = bNotifyBefore; _NotifyAfter = bNotifyAfter; }
public override void OnSetValue(LocationInterceptionArgs args)
{
INotify oNotify = args.Instance as INotify;
if (oNotify == null) return;
object oCurrentValue = args.GetCurrentValue();
object oProposedValue = args.Value;
if (object.Equals(oCurrentValue, oProposedValue)) return;
bool bCancel = false;
if (_NotifyBefore)
{
var oObj = args.Instance.GetType().GetEvent("PropertyBeforeChange");
// RAISE EVENT HERE
}
if (bCancel) return;
args.Value = oProposedValue;
args.ProceedSetValue();
if (_NotifyAfter)
{
var oObj = args.Instance.GetType().GetEvent("PropertyAfterChange");
// RAISE EVENT HERE
}
}
public object CreateInstance(AdviceArgs adviceArgs) { return this.MemberwiseClone(); }
public void RuntimeInitializeInstance() { }
}
}
having defined this interface and this attribute, i can use it as follows..
public class Test : INotify
{
public event PropertyBeforeChangeEventHandler PropertyBeforeChange;
public event PropertyAfterChangeEventHandler PropertyAfterChange;
[Notify]
public string Name { get; set; }
}
Test oTest = new Test();
oTest.PropertyBeforeChange += Test_PropertBeforeChange;
oTest.PropertyAfterChange += Test_PropertyAfterChange;
oTest.Name = "Asim";
void Test_PropertBeforeChange(object sender, string sPropertyName, object oCurrentValue, ref object oProposedValue, ref bool bCancel)
{
}
void Test_PropertyAfterChange(object sender, string sPropertyName, object oOldValue, object oNewValue)
{
}

List<T> firing Event on Change

I created a Class EventList inheriting List which fires an Event each time something is Added, Inserted or Removed:
public class EventList<T> : List<T>
{
public event ListChangedEventDelegate ListChanged;
public delegate void ListChangedEventDelegate();
public new void Add(T item)
{
base.Add(item);
if (ListChanged != null
&& ListChanged.GetInvocationList().Any())
{
ListChanged();
}
}
...
}
At the Moment I use it as a Property like this:
public EventList List
{
get { return m_List; }
set
{
m_List.ListChanged -= List_ListChanged;
m_List = value;
m_List.ListChanged += List_ListChanged;
List_ListChanged();
}
}
Now my Problem is, can I somehow handle if a new Object is referred to it or prevent that, so I do not have to do the event wiring stuff in the setter?
Of course, I can change the property to "private set" but I would like to be able to use the class as variable as well.

You seldom create a new instance of a collection class in a class. Instantiate it once and clear it instead of creating a new list. (and use the ObservableCollection since it already has the INotifyCollectionChanged interface inherited)
private readonly ObservableCollection<T> list;
public ctor() {
list = new ObservableCollection<T>();
list.CollectionChanged += listChanged;
}
public ObservableCollection<T> List { get { return list; } }
public void Clear() { list.Clear(); }
private void listChanged(object sender, NotifyCollectionChangedEventArgs args) {
// list changed
}
This way you only have to hook up events once, and can "reset it" by calling the clear method instead of checking for null or equality to the former list in the set accessor for the property.
With the changes in C#6 you can assign a get property from a constructor without the backing field (the backing field is implicit)
So the code above can be simplified to
public ctor() {
List = new ObservableCollection<T>();
List.CollectionChanged += OnListChanged;
}
public ObservableCollection<T> List { get; }
public void Clear()
{
List.Clear();
}
private void OnListChanged(object sender, NotifyCollectionChangedEventArgs args)
{
// react to list changed
}

ObservableCollection is a List with a CollectionChanged event
ObservableCollection.CollectionChanged Event
For how to wire up the event handler see answer from Patrick. +1
Not sure what you are looking for but I use this for a collection with one event that fires on add, remove, and change.
public class ObservableCollection<T>: INotifyPropertyChanged
{
private BindingList<T> ts = new BindingList<T>();
public event PropertyChangedEventHandler PropertyChanged;
// This method is called by the Set accessor of each property.
// The CallerMemberName attribute that is applied to the optional propertyName
// parameter causes the property name of the caller to be substituted as an argument.
private void NotifyPropertyChanged( String propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public BindingList<T> Ts
{
get { return ts; }
set
{
if (value != ts)
{
Ts = value;
if (Ts != null)
{
ts.ListChanged += delegate(object sender, ListChangedEventArgs args)
{
OnListChanged(this);
};
}
NotifyPropertyChanged("Ts");
}
}
}
private static void OnListChanged(ObservableCollection<T> vm)
{
// this will fire on add, remove, and change
// if want to prevent an insert this in not the right spot for that
// the OPs use of word prevent is not clear
// -1 don't be a hater
vm.NotifyPropertyChanged("Ts");
}
public ObservableCollection()
{
ts.ListChanged += delegate(object sender, ListChangedEventArgs args)
{
OnListChanged(this);
};
}
}

If you do not want to or can not convert to an Observable Collection, try this:
public class EventList<T> : IList<T> /* NOTE: Changed your List<T> to IList<T> */
{
private List<T> list; // initialize this in your constructor.
public event ListChangedEventDelegate ListChanged;
public delegate void ListChangedEventDelegate();
private void notify()
{
if (ListChanged != null
&& ListChanged.GetInvocationList().Any())
{
ListChanged();
}
}
public new void Add(T item)
{
list.Add(item);
notify();
}
public List<T> Items {
get { return list; }
set {
list = value;
notify();
}
}
...
}
Now, for your property, you should be able to reduce your code to this:
public EventList List
{
get { return m_List.Items; }
set
{
//m_List.ListChanged -= List_ListChanged;
m_List.Items = value;
//m_List.ListChanged += List_ListChanged;
//List_ListChanged();
}
}
Why? Setting anything in the EventList.Items will call your private notify() routine.

I have a Solution for when someone calls the Generic method from IList.add(object). So that you also get notified.
using System;
using System.Collections;
using System.Collections.Generic;
namespace YourNamespace
{
public class ObjectDoesNotMatchTargetBaseTypeException : Exception
{
public ObjectDoesNotMatchTargetBaseTypeException(Type targetType, object actualObject)
: base(string.Format("Expected base type ({0}) does not match actual objects type ({1}).",
targetType, actualObject.GetType()))
{
}
}
/// <summary>
/// Allows you to react, when items were added or removed to a generic List.
/// </summary>
public abstract class NoisyList<TItemType> : List<TItemType>, IList
{
#region Public Methods
/******************************************/
int IList.Add(object item)
{
CheckTargetType(item);
Add((TItemType)item);
return Count - 1;
}
void IList.Remove(object item)
{
CheckTargetType(item);
Remove((TItemType)item);
}
public new void Add(TItemType item)
{
base.Add(item);
OnItemAdded(item);
}
public new bool Remove(TItemType item)
{
var result = base.Remove(item);
OnItemRemoved(item);
return result;
}
#endregion
# region Private Methods
/******************************************/
private static void CheckTargetType(object item)
{
var targetType = typeof(TItemType);
if (item.GetType().IsSubclassOf(targetType))
throw new ObjectDoesNotMatchTargetBaseTypeException(targetType, item);
}
#endregion
#region Abstract Methods
/******************************************/
protected abstract void OnItemAdded(TItemType addedItem);
protected abstract void OnItemRemoved(TItemType removedItem);
#endregion
}
}

If an ObservableCollection is not the solution for you, you can try that:
A) Implement a custom EventArgs that will contain the new Count attribute when an event will be fired.
public class ChangeListCountEventArgs : EventArgs
{
public int NewCount
{
get;
set;
}
public ChangeListCountEventArgs(int newCount)
{
NewCount = newCount;
}
}
B) Implement a custom List that inherits from List and redefine the Count attribute and the constructors according to your needs:
public class CustomList<T> : List<T>
{
public event EventHandler<ChangeListCountEventArgs> ListCountChanged;
public new int Count
{
get
{
ListCountChanged?.Invoke(this, new ChangeListCountEventArgs(base.Count));
return base.Count;
}
}
public CustomList()
{ }
public CustomList(List<T> list) : base(list)
{ }
public CustomList(CustomList<T> list) : base(list)
{ }
}
C) Finally subscribe to your event:
var myList = new CustomList<YourObject>();
myList.ListCountChanged += (obj, e) =>
{
// get the count thanks to e.NewCount
};