I'm trying to raise PropertyChangedEventHandler from a CollectionChanged callback. It gets raised, but it doesn't reach the subscriber.
Perhaps I can't just treat an EventHandler like a variable? Although I have done so without issue in the past, it's just raising it from within another event where I am having issue.
Any help appreciated, thanks.
using System;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.ComponentModel;
namespace Fire
{
/// <summary>
/// Simple class implementing INotifyPropertyChanged
/// I want to raise PropertyChanged whenever the ObservableCollection changes.
/// </summary>
public class Model : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged = delegate { };
public ObservableCollection<int> Collection { get; set; }
public Model()
{
Collection = new ObservableCollection<int>();
// In theory it should be sorted out here:
Utils.RaisePropertyChangedWhenCollectionChanged(this, Collection, PropertyChanged, "Collection");
}
}
/// <summary>
/// I want to wrap the "If CollectionChanged then raise PropertyChanged" logic in a utility method".
/// </summary>
public class Utils
{
public static void RaisePropertyChangedWhenCollectionChanged(object owner, INotifyCollectionChanged collection, PropertyChangedEventHandler eventHandler, string propertyName)
{
collection.CollectionChanged += (object sender, NotifyCollectionChangedEventArgs e) =>
{
eventHandler(owner, new PropertyChangedEventArgs(propertyName));
};
}
}
class Program
{
static void Main(string[] args)
{
Model model = new Model();
model.PropertyChanged += model_PropertyChanged;
// But the problem is that PropertyChanged does not fire, even when the collection is changed.
model.Collection.Add(2);
}
static void model_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
// This does not get called!
Console.Out.WriteLine(String.Format("{0}", e.PropertyName));
}
}
}
In this call:
Utils.RaisePropertyChangedWhenCollectionChanged(this, Collection, PropertyChanged, "Collection");
... you're passing in the current value of PropertyChanged
, which is a single no-op delegate. Instead, you want it to raise the property changed event for whatever handlers are present when the event is raised. For example:
Utils.RaisePropertyChangedWhenCollectionChanged
(this, Collection,
(sender, args) => PropertyChanged(sender, args),
"Collection");
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