C# Add event to value inside Dictionary<TKey, TValue>

Question

I'm trying to add an event to the value of a dictionary. I made my own ObservableDictionary with an event on the Add button, but now I'm trying to do the same for the value. The dictionary looks like Dictionary<string, ObservableCollection<string>> .

The calling function:

public void AddExtension(string key, string value)
{
    if (_settings.ExtensionsPerFolder.ContainsKey(key))
    {
        _settings.ExtensionsPerFolder[key].Add(value);
        var values = _settings.ExtensionsPerFolder[key];
        values.Add(value);
        _settings.ExtensionsPerFolder[key] = values;
    }
    else
        _settings.ExtensionsPerFolder.Add(key, new ObservableCollection<string> { value });
}

My own dictionary implementation:

public class ObservableDictionary<TKey, TValue> : Dictionary<TKey, TValue>
{
    public event EventHandler CollectionChanged;

    public new TValue this[TKey key]
    {
        get => base[key];
        set
        {
            base[key] = value;
            OnCollectionChanged();
        }
    }

    public new void Add(TKey key, TValue value)
    {
        base.Add(key, value);
        OnCollectionChanged();
    }

    protected void OnCollectionChanged() => CollectionChanged?.Invoke(this, EventArgs.Empty);
}

The _settings.ExtensionsPerFolder[key].Add(value) doesn't trigger the OnCollectionChanged event, but the _settings.ExtensionsPerFolder[key] = values does.

[EDIT] The file in which the Dictionary is initialized:

public class Settings
    {
        [JsonIgnore]
        public string SettingsPath { get; } = "Settings.json";
        public ObservableCollection<string> Directories { get; set; } = new ObservableCollection<string>();
        public ObservableDictionary<string, ObservableCollection<string>> ExtensionsPerFolder { get; set; } = new ObservableDictionary<string, ObservableCollection<string>>();

        public Settings() { }

        public void CollectionChanged()
        {
            Directories.CollectionChanged += CollectionChanged;
            ExtensionsPerFolder.CollectionChanged += CollectionChanged;
        }

        private void CollectionChanged(object sender, EventArgs e)
        {
            try
            {
                using StreamWriter writer = new StreamWriter(SettingsPath);
                writer.WriteLine(this.ToJson());
            }
            catch (Exception ex)
            {
                Logger log = new Logger();
                log.Log($"Unable to save: {ex.ToString()}");
            }
        }
    }

Is there any way that I can achieve this power of event control, or do I have to fiddle with the Add functionality within my own Dictionary for it to work.

Thanks in advance.

Answer 1

You have a collection of collections and you've only ever subscribed to observe the outer collection. You've subscribed to ExtensionsPerFolder.CollectionChanged which will tell you when you do something like ExtensionsPerFolder[key] = values , but you haven't subscribed to each inner collection. In this case values should be an ObservableCollection<string> .

Each time you create a new ObservableCollection<string> , you'll want to subscribe to it.

Here's where you created a new one:

_settings.ExtensionsPerFolder.Add(key, new ObservableCollection<string> { value });

You'll also want to add a CollectionChanged handler for this new collection at this point in your code. That way a statement like _settings.ExtensionsPerFolder[key].Add(value) will trigger a CollectionChanged event on that particular collection.

I'll leave it to you to decide what you want that event handler to do.