IReadOnlyCollection with notifications

Question

It is not related to GUI. I have a class with:

1. Private List, which is edited inside the class.
2. Open IReadOnlyCollection property for access to private List
3. Public event for notification on List changing

A list stores objects with properties. The class can changed an item's properties and notify about it. The user can only read an item's properties. I only picked this option.

class MortarInfo
{
 public double Angle { get; private set; }
 public bool State { get; private set; }
 public MortarInfo(double angle, bool state)
 {
 Angle = angle;
 State = state;
 }
}
class Mortars
{
 private List<MortarInfo> _mortarsInfo;
 private ReadOnlyCollection<MortarInfo> _readOnlyMortarsInfo;
 public Mortars()
 {
 _mortarsInfo = new List<MortarInfo>();
 _readOnlyMortarsInfo = _mortarsInfo.AsReadOnly();
 }
 public ReadOnlyCollection<MortarInfo> MortarsInfo
 {
 get { return _readOnlyMortarsInfo; }
 }
 public event ListChangedEventHandler MortarsInfoChanged;
 public void UpdateAngle(int index, double newAngle)
 {
 if (_mortarsInfo[index].Angle != newAngle)
 {
 _mortarsInfo[index] = new MortarInfo(newAngle, _mortarsInfo[index].State);
 if (MortarsInfoChanged != null)
 {
 var arg = new ListChangedEventArgs(ListChangedType.ItemChanged, index);
 MortarsInfoChanged(this, arg);
 }
 }
 }
}

Answer 1

It seems good but I have some comments on this,

1. Why do you create a new ListItem in every property change and not just replace to old property with the new one?

   _list[index].Property1 = property1;
   

2. You raise the event without null check. Do this:

   var listChanged = ListChanged;
   if (listChanged != null)
    listChanged(this,new ListChangedEventArgs(ListChangedType.ItemChanged, index));
   

3. As a side note, if Property1 or Property2 are complex objects, It's recommended to create for them you own equal methods (Equal, GetHashCode, == and !=). If the are generic, implement IEquatable<T>

• Nodon: 1. I create a new ListItem, because user don't to be able to hange anything. 2. In project i use Extension methods to raise event. It have a check. 3. It a good idea.
• RubberDuck: It'd be helpful to explain why the temporary variable is needed in the null check. I.e. The handler could go null between the check and call without it.