ObservableDictionary for c#

Question

I'm trying to use following implementation of the ObservableDictionary: ObservableDictionary (C#).

When I'm using following code while binding the dictionary to a DataGrid:

ObserveableDictionary<string,string> dd=new ObserveableDictionary<string,string>();
....
dd["aa"]="bb";
....
dd["aa"]="cc";

at dd["aa"]="cc"; I'm getting following exception

Index was out of range. Must be non-negative and less than the size of the 
collection. Parameter name: index

This exception is thrown in CollectionChanged(this, new NotifyCollectionChangedEventArgs(action, newItem, oldItem) in the following method:

private void OnCollectionChanged(NotifyCollectionChangedAction action, KeyValuePair<TKey, TValue> newItem, KeyValuePair<TKey, TValue> oldItem)
{
  OnPropertyChanged();

  if (CollectionChanged != null) CollectionChanged(this, new NotifyCollectionChangedEventArgs(action, newItem, oldItem));
}

The index param seems to correspond to KeyValuePair<TKey, TValue> oldItem.

How can KeyValuePair<TKey, TValue> be out of range, and what should I do to make this work?

Answer 1

here's what I did in the end:

[Serializable]
public class ObservableKeyValuePair<TKey,TValue>:INotifyPropertyChanged
{
    #region properties
    private TKey key;
    private TValue value;

    public TKey Key
    {
        get { return key; }
        set
        {
            key = value;
            OnPropertyChanged("Key");
        }
    }

    public TValue Value
    {
        get { return value; }
        set
        {
            this.value = value;
            OnPropertyChanged("Value");
        }
    } 
    #endregion

    #region INotifyPropertyChanged Members

    [field:NonSerialized]
    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged(string name)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(name));
    }

    #endregion
}

[Serializable]
public class ObservableDictionary<TKey,TValue>:ObservableCollection<ObservableKeyValuePair<TKey,TValue>>, IDictionary<TKey,TValue>
{

    #region IDictionary<TKey,TValue> Members

    public void Add(TKey key, TValue value)
    {
        if (ContainsKey(key))
        {
            throw new ArgumentException("The dictionary already contains the key");
        }
        base.Add(new ObservableKeyValuePair<TKey, TValue>() {Key = key, Value = value});
    }

    public bool ContainsKey(TKey key)
    {
        //var m=base.FirstOrDefault((i) => i.Key == key);
        var r = ThisAsCollection().FirstOrDefault((i) => Equals(key, i.Key));

        return !Equals(default(ObservableKeyValuePair<TKey, TValue>), r);
    }

    bool Equals<TKey>(TKey a, TKey b)
    {
        return EqualityComparer<TKey>.Default.Equals(a, b);
    }

    private ObservableCollection<ObservableKeyValuePair<TKey, TValue>> ThisAsCollection()
    {
        return this;
    }

    public ICollection<TKey> Keys
    {
        get { return (from i in ThisAsCollection() select i.Key).ToList(); }
    }

    public bool Remove(TKey key)
    {
        var remove = ThisAsCollection().Where(pair => Equals(key, pair.Key)).ToList();
        foreach (var pair in remove)
        {
            ThisAsCollection().Remove(pair);
        }
        return remove.Count > 0;
    }

    public bool TryGetValue(TKey key, out TValue value)
    {
        value = default(TValue);
        var r = GetKvpByTheKey(key);
        if (!Equals(r, default(ObservableKeyValuePair<TKey, TValue>)))
        {
            return false;
        }
        value = r.Value;
        return true;
    }

    private ObservableKeyValuePair<TKey, TValue> GetKvpByTheKey(TKey key)
    {
        return ThisAsCollection().FirstOrDefault((i) => i.Key.Equals(key));
    }

    public ICollection<TValue> Values
    {
        get { return (from i in ThisAsCollection() select i.Value).ToList(); }
    }

    public TValue this[TKey key]
    {
        get
        {
            TValue result;
            if (!TryGetValue(key,out result))
            {
                throw new ArgumentException("Key not found");
            }
            return result;
        }
        set
        {
            if (ContainsKey(key))
            {
                GetKvpByTheKey(key).Value = value;
            }
            else
            {
                Add(key, value);
            }
        }
    }

    #endregion

    #region ICollection<KeyValuePair<TKey,TValue>> Members

    public void Add(KeyValuePair<TKey, TValue> item)
    {
        Add(item.Key, item.Value);
    }

    public bool Contains(KeyValuePair<TKey, TValue> item)
    {
        var r = GetKvpByTheKey(item.Key);
        if (Equals(r, default(ObservableKeyValuePair<TKey, TValue>)))
        {
            return false;
        }
        return Equals(r.Value, item.Value);
    }

    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
    {
        throw new NotImplementedException();
    }

    public bool IsReadOnly
    {
        get { return false; }
    }

    public bool Remove(KeyValuePair<TKey, TValue> item)
    {
        var r = GetKvpByTheKey(item.Key);
        if (Equals(r, default(ObservableKeyValuePair<TKey, TValue>)))
        {
            return false;
        }
        if (!Equals(r.Value,item.Value))
        {
            return false ;
        }
        return ThisAsCollection().Remove(r);
    }

    #endregion

    #region IEnumerable<KeyValuePair<TKey,TValue>> Members

    public new IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
    {
        return (from i in ThisAsCollection() select new KeyValuePair<TKey, TValue>(i.Key, i.Value)).ToList().GetEnumerator();
    }

    #endregion
}

This implementation looks and feels like dictionary to the user and like ObservableCollection to WPF

Answer 2

Similar data structure, to bind to Dictionary type collection

http://drwpf.com/blog/2007/09/16/can-i-bind-my-itemscontrol-to-a-dictionary/

It provides a new Data structure ObservableDictionary and fires PropertyChanged in case of any change to underlying Dictionary.

Answer 3

I ended up writing a class to hold the Key-Value pair and using a collection of that class. I'm using Caliburn Micro which is where the BindableCollection comes from, but an ObservableCollection should work the same way. I use the MVVM pattern.

the viewmodel

using Caliburn.Micro;

private BindableCollection<KeyValuePair> _items;

public BindableCollection<KeyValuePair> Items
{
  get { return _items; }

  set
  {
    if (_items != value)
    {
      _items = value;
      NotifyOfPropertyChange(() => Items);
    }
  }
}

the custom keyValuePair

public class KeyValuePair 
{
  public string Key { get; set; }

  public string Value { get; set; }
}

and in the view

<ItemsControl ItemsSource="{Binding Items}">
  <ItemsControl.ItemTemplate>
    <DataTemplate>
      <Grid>
        <Grid.ColumnDefinitions>
          <ColumnDefinition Width="*" />
          <ColumnDefinition Width="2*" />
          <ColumnDefinition Width="Auto" />
        </Grid.ColumnDefinitions>

        <TextBox Grid.Column="0"
                 Text="{Binding Key, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
        <TextBox Grid.Column="1"
                 Text="{Binding Value, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
      </Grid>
    </DataTemplate>
  </ItemsControl.ItemTemplate>
</ItemsControl>

It bothers me that I can't just bind to a dictionary, but I find this much easier and cleaner than writing an ObservableDictionary from scratch and worrying about the change notifications.

Answer 4

ObservableDictionary was added to the .Net Framework at version 4.5:-

https://zamjad.wordpress.com/2012/10/12/observabledictionary-in-net-4-5/

Here is a link to the latest source code:-

https://referencesource.microsoft.com/#PresentationFramework/src/Framework/MS/Internal/Annotations/ObservableDictionary.cs