Question

My issue seems to be “scope”, though I’m not certain that’s the right terminology. I want to notify a read-only list to re-evaluate itself when a property within a custom object is set. I believe it is simply not aware of it’s existence. Maybe there is an easy way around this I cannot think of, but I’m drawing a blank.

I find this hard to put into words, so here’s simplified code with my comments on what I expect to happen.

Properties within object in which I am databinding to:

private CvarAspectRatios _aspectRatio = new CvarAspectRatios("none", GetRatio());
public CvarAspectRatios AspectRatio
{
    get { return _aspectRatio; }
    set
    {                                                 // This setter never gets hit since I bind to this 
        if (value != null)                            // object's 'Value' property now.
        {
            _aspectRatio = value;
            NotifyPropertyChanged("AspectRatio");
            NotifyPropertyChanged("ResolutionList");  // I want to inform ResolutionList
        }                                             // that it needs to repopulate based
    }                                                 // on this property: AspectRatio
}

private ResolutionCollection _resolutionList = ResolutionCollection.GetResolutionCollection();
public ResolutionCollection ResolutionList
{
   get 
   {
       ResolutionCollection list = new ResolutionCollection();
       if (AspectRatio != null && AspectRatio.Value != null)
       {
           foreach (Resolutions res in _resolutionList.Where(i => i.Compatibility == AspectRatio.Value.Compatibility))
           {
               list.Add(res);
           }
           return list;
       }
       return _resolutionList;
   }
}

CvarAspectRatios Class:

public class CVarAspectRatios : INotifyPropertyChanged
{
    private string _defaultValue;
    public string DefaultValue
    {
        get { return _defaultValue; }
        set { _defaultValue = value; NotifyPropertyChanged("DefaultValue"); }
    }

    private AspectRatios _value;
    public AspectRatios Value
    {
        get { return _value; }
        set 
        { 
            _value = value; 
            NotifyPropertyChanged("Value"); 
            NotifyPropertyChanged("ResolutionList");  // This value gets set, and I'd like for ResolutionList to update
        }                                             // but it cannot find ResolutionList. No errors or anything. Just
    }                                                 // no update.

    public AspectRatios() { }

    public AspectRatios(string defaultValue, AspectRatios val)
    {
        DefaultValue = defaultValue;
        Value = val;
    }

    // Implementation of INotifyPropertyChanged snipped out here
}

What do you folks think? If you’d like a sample application I can whip one up.

Answer 1

Since CVarAspectRatios implements INotifyPropertyChanged, you can have the viewmodel class subscribe to the PropertyChanged event for the AspectRatio.

public class YourViewModel 
{
    public YourViewModel()
    {
        AspectRatio.PropertyChanged += AspectRatio_PropertyChanged;
    }

    void AspectRatio_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "Value")
            NotifyPropertyChanged("ResolutionList");
    }        
}

Just bear in mind that if you discard that AspectRatio object (if the object reference changes and not just the value property of that object), you should unsubscribe from the event on the discarded one.