Question

my application is a basic download app that allows users to download files from each other (a very basic kazaa :-))

Well for each download im displaying a progressbar and i want it updated according to the real download progress.

I have an observablecollection that holds a downloadInstance object which holds a progress property.

once i update the progress property the observablecollection change event probably isnt fired and the progressbar stays without any visual progress.

here is my threadsaveobservablecollection class

public class ThreadSafeObservableCollection<T> : ObservableCollection<T>
{
    public override event NotifyCollectionChangedEventHandler CollectionChanged;

    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        NotifyCollectionChangedEventHandler CollectionChanged = this.CollectionChanged;
        if (CollectionChanged != null)
            foreach (NotifyCollectionChangedEventHandler nh in CollectionChanged.GetInvocationList())
            {
                DispatcherObject dispObj = nh.Target as DispatcherObject;
                if (dispObj != null)
                {
                    Dispatcher dispatcher = dispObj.Dispatcher;
                    if (dispatcher != null && !dispatcher.CheckAccess())
                    {
                        dispatcher.BeginInvoke(
                            (Action)(() => nh.Invoke(this,
                                new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset))),
                            DispatcherPriority.DataBind);
                        continue;
                    }
                }
                nh.Invoke(this, e);
            }
    }

}

This is the initialization process

uploadActiveInstances = new ThreadSafeObservableCollection<instance>();
instance newInstance = new instance() { File = file, User = user };
uploadActiveInstances.Add(newInstance);

and finally here is my instance class

public class instance
{
    public FileShareUser User { get; set; }
    public SharedFile File { get; set; }
    public int Progress { get; set; }
}

how can i raise the change event once a property of an instance changes (progress++) ?

Answer 1

The ObservableCollection will raise an event when IT changes (e.g. items are added/removed) but not when the items it holds change.

To raise an event when your items change, your instance class must implement the INotifyPropertyChanged interface.

For example:

public class instance : INotifyPropertyChanged
{
    private int progress;
    public int Progress 
    {
        get { return progress; }
        set
        {
            if (progress != value)
            {
                progress = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("Progress"));
                }
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    /* Do the same with the remaining properties */
    public string User { get; set; }
    public string File { get; set; }

}

You will see that now, when you change the progress it WILL get updated in the UI.
In the code above, since I don’t raise the PropertyChanged event for User or File, they will not get updated in the UI when you change them.