Question

I have a object that is created through deserialization of some XML. I used Visual Studio’s tool to generate the XSD from the vendor mockup XML. Then using the XSD tool I got classes from them. I set the XSD tool so that it would make the generated classes be INotifyPropertyChanged.

Now I’m trying to display this object in a “tab” on my WPF application. I want a “dirty” indicator whenever someone makes a change. The issue is that this object, being generated classes from generated XSD is not the prettiest structure. The display for this object is does not mimic its data structure. I thought of creating display objects (not using MMVM ATM) and using those to bind my changes to and then persist those changes to the object as a data object. I would essentially just throw out my current display to do this since I’m now just adding a check for if there were edits.

My thought is to reflect across the object and set the PropertyChanged event for every property I come across (walking through the graph of objects and properties). My reflection fu is failing me and I’m also probably making some short-sighted mistakes.

Here is the code I’ve written thus far:

void SetupPropertyChanged(INotifyPropertyChanged component)
    {
        component.PropertyChanged += CAMConfig_PropertyChanged;

        Type componentType = component.GetType();

        foreach (PropertyInfo info in componentType.GetProperties())
        {
            Type[] types =
                info.PropertyType.FindInterfaces((a, b) => { return a.ToString() == b.ToString(); }, typeof(INotifyPropertyChanged));

            bool isINotify = types.Contains(typeof(INotifyPropertyChanged));


            if (isINotify)
                this.SetupPropertyChanged((INotifyPropertyChanged)info.GetValue(component, new object[] { }));
        }
    }

I think I’m running into Observable collection property type issues as its throwing an exception when I’m traversing my object. It also just hit me that I don’t know if this object structure would have circular references.

Can someone help me work out this code so that I can traverse the object graph. Right now I’m not too concerned about the possibility of circular references, but if a solution presents itself that prevents that situation it would be very, very helpful!

Based on Karel’s answer I’ve created this “helper” class:

    public static class NotifyPropertyChangedHelper
{
    public delegate void ChangeOccuredHandler(object sender);

    public static void SetupPropertyChanged(INotifyPropertyChanged component, ChangeOccuredHandler changedHandler)
    {
        SetupPropertyChanged(new List<object>(), component, changedHandler);
    }

    static void SetupPropertyChanged(IList<object> closed, INotifyPropertyChanged component, ChangeOccuredHandler changedHandler)
    {
        if (closed.Contains(component)) return; // event was already registered

        closed.Add(component); //adds the property that is to be processed

        //sets the property changed event if the property isn't a collection
        if (!(component is INotifyCollectionChanged))
            component.PropertyChanged += (sender, e) =>
                {
                    changedHandler(sender);
                };

        /*
         * If the component is an enumerable there are two steps. First check to see if it supports the INotifyCollectionChanged event.
         * If it supports it add and handler on to this object to support notification.  Next iterate through the collection of objects
         * to add hook up their PropertyChangedEvent.
         * 
         * If the component isn't a collection then iterate through its properties and attach the changed handler to the properties.
         */
        if (component is IEnumerable<object>)
        {
            if (component is INotifyCollectionChanged)
            {
                //((INotifyCollectionChanged)component).CollectionChanged += collectionHandler;
                ((INotifyCollectionChanged)component).CollectionChanged += (sender, e) =>
                    {
                        changedHandler(sender);
                    };
            }

            foreach (object obj in component as IEnumerable<object>)
            {
                if (obj is INotifyPropertyChanged)
                    SetupPropertyChanged(closed, (INotifyPropertyChanged)obj, changedHandler);
            }
        }
        else
        {
            foreach (PropertyInfo info in component.GetType().GetProperties())
            {
                var propertyValue = info.GetValue(component, new object[] { });
                var inpc = propertyValue as INotifyPropertyChanged;
                if (inpc == null) continue;
                SetupPropertyChanged(closed, inpc, changedHandler);
            }
        }
    }
}

Answer 1

Keep a list of properties (components) for which you’ve already registered the event and make your function recursive. And you can cast component to INotifyPropertyChanged directly.

void SetupPropertyChanged(IList<object> closed, INotifyPropertyChanged component)  
{
  if(closed.Contains(component)) return; // event was already registered

  closed.Add(component);

  component.PropertyChanged += CAMConfig_PropertyChanged;            
  foreach (PropertyInfo info in componentType.GetProperties())          
  {
    var propertyValue = info.GetValue(component, new object[] { });
    var inpc = propertyValue as INotifyPropertyChanged;
    if(inpc == null) continue;
    this.SetupPropertyChanged(closed, inpc);
  }  
}