Cascaded PropertyChangedEvents crashes with DataGridView

Here is the code fragment of our BindingList and the business objects. We bound the business objects via a BindingSource to the DataGridView.

using System; using System.Collections.Generic; using System.Text; using System.ComponentModel; using System.Reflection; using System.Collections; using System.Diagnostics; using System.Windows.Forms; namespace TestPropertyChanged { public class MyBindingList<T> : BindingList<T> { public event EventHandler ChildObjectChanged; void Subscribe(object item) { INotifyPropertyChanged newObject = item as INotifyPropertyChanged; if (newObject != null) { newObject.PropertyChanged += new PropertyChangedEventHandler(newObject_PropertyChanged); } } protected override void InsertItem(int index, T item) { base.InsertItem(index, item); Subscribe(item); } protected override object AddNewCore() { object newObject = base.AddNewCore(); Subscribe(newObject); return newObject; } void newObject_PropertyChanged(object sender, PropertyChangedEventArgs e) { if (ChildObjectChanged != null) ChildObjectChanged(this, EventArgs.Empty); } } public class RawMaterial : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; private double? quantity; public double? Quantity { get { return quantity; } set { quantity = value; if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("Quantity")); } } private double? pricePerUnit; public double? PricePerUnit { get { return pricePerUnit; } set { pricePerUnit = value; if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("PricePerUnit")); } } public double? Price { get { return pricePerUnit * quantity; } } } public class Calculation : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; private MyBindingList<RawMaterial> rawMaterials = new MyBindingList<RawMaterial>(); public MyBindingList<RawMaterial> RawMaterials { get { return rawMaterials; } set { rawMaterials = value; } } public Calculation() { rawMaterials.ChildObjectChanged += new EventHandler(rawMaterials_ChildObjectChanged); } void rawMaterials_ChildObjectChanged(object sender, EventArgs e) { if (RawMaterials.Count == 0) { rawMaterialCosts = null; } else { rawMaterialCosts = 0; foreach (RawMaterial material in RawMaterials) { rawMaterialCosts += material.Price; } } if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("RawMaterialCosts")); } private double? rawMaterialCosts = null; public double? RawMaterialCosts { get { return rawMaterialCosts; } } } }

And to relate this back to your first post - your BindingList implementation should fire ListChanged events of type ItemChanged when any child property changes (even a related one). Your other types would then only need to listen to ListChanged events on your BindingList.

Also note that you need to hook/unhook events in several spots as shown in my sample above.

Joe

The DataGridView doesn't listen to PropertyChanged events - it only listens to ListChanged events. If you're binding through a BindingSource, the BindingSource will translate some PropertyChaned events to ListChanged. From you've provided, I can't tell what's happening (there are no issues related to what you're describing) however I can see where your solution will lead to problems (such as recursive property changed events getting fired, memory leaks, events getting fired on disposed objects). In order to determine the exact issue, I'd need a small repro.

Also, if you're going to sub-class BindingList<T>, I'd recommend you control child change notification through ListChanged events. When Windows Forms controls are bound to lists, they don't listen to PropertyChanged events. The best way to handle child PropertyChanged events in a sub-classed BindingList<T> is to turn them into ListChanged events (which we will automatically do in BindingList<T> post B2). The sample I provided does this and I think you'll find this fits more naturally into the Windows Forms data binding model.

Joe