I'm creating a list of checkboxes "On the fly" from a Flagged Enum using a converter, in MVVM WPF application. The bound property is an int, that represents a flagged enum. This is my converter that converts from the int, to an ObservableDictionary<int, bool>.
public class AccessListConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
int realValue;
switch (value)
{
case int intValue:
realValue = intValue;
break;
case AccessEnum enumValue:
realValue = (int)enumValue;
break;
default:
return Binding.DoNothing;
}
List<AccessEnum> accessComponents = Enum.GetValues(typeof(AccessEnum)).Cast<AccessEnum>().Where(r => ((AccessEnum)realValue & r) == r).Select(r => r).ToList();
ObservableDictionary<int, bool> accessDictionary = new ObservableDictionary<int, bool>(Enum.GetValues(typeof(AccessEnum)).Cast<int>().Select(i => i).ToDictionary(i => i, i => accessComponents.Contains((AccessEnum) i)));
accessDictionary.Remove(0);
return accessDictionary;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is Dictionary<int, bool> intDict))
{
throw new NotImplementedException();
}
return intDict.Sum(x => x.Value ? x.Key : 0);
}
}
The point is that the user can pick and choose which enums to enable for the property. I figured using a converter would make sense, but I'm having a hard time getting the converter to trigger it's "ConvertBack" method, when a checkbox is ticked/unticked.
Here are my bindings in the Xaml:
<ItemsControl ItemsSource="{Binding Access, UpdateSourceTrigger=PropertyChanged, Converter={StaticResource AccessListConverter}}" Margin="87,0,10,0">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel CanVerticallyScroll="False" Margin="0"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<CheckBox VerticalAlignment="Center" Margin="6,0,0,0" Content="{Binding Key, Converter={StaticResource AccessStringConverter}, UpdateSourceTrigger=PropertyChanged}"
IsChecked="{Binding Value, UpdateSourceTrigger=PropertyChanged}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
And now we get to the Observable Dictionary This is what my implementation of OBservableDictionary looks like (Irrelevant parts removed and the rest shrunk):
[Serializable]
public class ObservableDictionary<TKey, TValue> :
ObservableCollection<ObservableKeyValuePair<TKey, TValue>>, IDictionary<TKey, TValue>
{
public ObservableDictionary() {}
public ObservableDictionary(Dictionary<TKey, TValue> dictionary) : this()
{
foreach (TKey key in dictionary.Keys) { Add(key, dictionary[key]); }
}
public ObservableDictionary(ObservableDictionary<TKey, TValue> dictionary) : this()
{
foreach (TKey key in dictionary.Keys) { Add(key, dictionary[key]); }
}
public void Add(TKey key, TValue value)
{
if (ContainsKey(key)) { throw new ArgumentException("The dictionary already contains the key"); }
Add(new ObservableKeyValuePair<TKey, TValue>() { Key = key, Value = value });
}
public ICollection<TKey> Keys => (from i in ThisAsCollection() select i.Key).ToList();
public ICollection<TValue> Values => (from i in ThisAsCollection() select i.Value).ToList();
public TValue this[TKey key]
{
get { if (!TryGetValue(key, out TValue result)) {throw new ArgumentException("Key not found"); } return result; }
set { if (ContainsKey(key)) { GetKvpByTheKey(key).Value = value; } else { Add(key, value); } }
}
}
I then implemented a collectionChanged code snippet form StackOverflow
void TrulyObservableCollection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.NewItems != null) foreach (object item in e.NewItems){ ((INotifyPropertyChanged) item).PropertyChanged += item_PropertyChanged; }
if (e.OldItems != null) foreach (object item in e.OldItems) { ((INotifyPropertyChanged) item).PropertyChanged -= item_PropertyChanged;}
}
void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
NotifyCollectionChangedEventArgs a = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset);
OnCollectionChanged(a);
}
And added CollectionChanged += TrulyObservableCollection_CollectionChanged; to the empty constructor.
But no dice. With hours of searching, I've still come up empty. ConvertBack never gets triggered. I gather it may be because the collection itself isn't actually changing, but how then can I force an update? Any help much appreciated :)
Edit: I might have discovered the answer to my own question in the form of this comment: https://stackoverflow.com/a/59637445/3390519 I'll give it a go!
