C# Nested Class

Question

I have a class Animal. Within the class Animal I have a list of another class called Dogs.

class Animal
{
  List<Dog> Dogs;
  int CountNeutedDogs;


  class Dog
  {
     // some properties
     boolean neuted;
   }
 }

It's possible that the list can contain about 500 dogs at any one time. I want to have an event so that if the value of neuted property in a dog changes the CountNeutedDogs is informed and updated. How do I do this?

Edit

I should explain the list Dogs is bound to a datagrid. The user can change the neuted property from false to true and vice versa. I have a get & set for the property. So the neuted value can change and I need to update the CountNeutedDogs value which is why I was thinking of using an event but not sure how to do it.

I think creating a nested class for `Dog` is a little bit strange. I would not create it as an inner class, because a `Dog` could also be used in a `Mammal` class. — Jeroen van Langen, Sep 30 '13 at 09:19
Might I suggest that your object modelling is a little unusual. In the real world an Animal does not HAVE A dog (or dogs), rather for example a Pound might HAVE A collection of dogs, and a dog IS an Animal (i.e. is a subclass of). — Surfbutler, Sep 30 '13 at 09:19
I appreciate that the object modelling is probably not correct. I just created this example (should have used a better one, lesson learnt for next time!) to find out how I would create an event in my Dog Class to update the property in my Animal class. — mHelpMe, Sep 30 '13 at 09:22
you can declare an event for value changed, and put the logic you want in an event handler. this is a possible duplicate for your question: [link](http://stackoverflow.com/questions/9963809/value-changed-eventhandler) — Moha the almighty camel, Sep 30 '13 at 09:27

score 4 · Answer 1 · edited Sep 30 '13 at 09:11

4

If you make CountNeutedDogs a property like so, it will always be correct without events updating:

int CountNeutedDogs
{
    get
    {
        return this.Dogs.Where(d => d.neuted).Count();
    }
}

edited Sep 30 '13 at 09:11

Jeroen van Langen

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answered Sep 30 '13 at 09:11

Ashigore

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@jeroen-van-langen Thanks for fixing the count, I just noticed I forgot to add it :) – Ashigore Sep 30 '13 at 09:13
I think this is a nice solution you provided. No need to provide the same answer :). +1 – Jeroen van Langen Sep 30 '13 at 09:15
The OP requested a method of updating the `NeutedDogsCount` when a Dog is added. So i suggested something. – Jeroen van Langen Sep 30 '13 at 09:40

Jeroen van Langen · Accepted Answer · 2013-09-30T10:26:58.333

This is a follow-up on the Comments:

I made an example, (not tested!!) how you can solve this by implementing the ObservableCollection and INotifyPropertyChanged

public class Dog : INotifyPropertyChanged
{
    private bool _isNeutered;

    public bool IsNeutered 
    {
        get { return _isNeutered; }
        set 
        {
            if (_isNeutered != value)
            {
                _isNeutered = value;
                if (PropertyChanged != null)
                    PropertyChanged(this, new PropertyChangedEventArgs("IsNeutered"));
            }
        } 
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

public class Animals : INotifyPropertyChanged
{
    private ObservableCollection<Dog> _dogs = new ObservableCollection<Dog>();

    public Animals()
    {
        _dogs.CollectionChanged += Dogs_CollectionChanged;
    }


    // NOTE, I haven't checked this!! But I think it should be something like this:
    private void Dogs_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                foreach (INotifyPropertyChanged item in e.NewItems.OfType<INotifyPropertyChanged>())
                    item.PropertyChanged += Item_PropertyChanged;
                break;

            case NotifyCollectionChangedAction.Reset:
            case NotifyCollectionChangedAction.Remove:
                foreach (INotifyPropertyChanged item in e.OldItems.OfType<INotifyPropertyChanged>())
                    item.PropertyChanged -= Item_PropertyChanged;
                break;
        }

        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs("NeuteredDogsCount"));
    }

    private void Item_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs("NeuteredDogsCount"));
    }

    public IEnumerable<Dog> Dogs 
    { 
        get { return _dogs; } 
    }

    public int NeuteredDogsCount
    {
        get
        {
            return Dogs.Where(dog => dog.IsNeutered).Count();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

So when the collection changes, the notify of the NeuteredDogsCount property is sent. This way the bounded controls will re-evaluate the NeuteredDogsCount property.

Instead of 'normal' properties, the IsNeutered can be changed to a DependencyProperty.

thanks for the code example. Is it possible to do something similar without making the Dog list an ObservableCollection? — mHelpMe, Sep 30 '13 at 09:40
You can check over here: _BindingList_ http://msdn.microsoft.com/en-us/library/ms132679.aspx — Jeroen van Langen, Sep 30 '13 at 09:43
@JeroenvanLangen This is quite an interesting way to do it, however, I don't believe this handles the case where a dog in the list is updated externally. Wouldn't you need to attach and detach to each Dog's PropertyChanged event when they are added and removed? — Ashigore, Sep 30 '13 at 10:00

C# Nested Class

2 Answers2