Question

I have a custom base type called MyEntityBase for the superclass of the types in my auto-generated DataContext class, MyContext. In attempting to create a mock data context, I decided to implement INotifyPropertyChanged on MyEntityBase so I can generically track changes.

Here’s what my class looks like:

public abstract class MyEntityBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
}

Based on this class, I have created a generic Repository<T> class for storing instances of a specific type of entity. The basic idea behind this class is to provide methods similar to a datacontext, but instead backed by an in-memory list. I also want to simulate tracking changes, since the change set is important to the business logic of our application for syncing with 3rd-party systems.

Here is a basic shell implementation of Repository<T>:

public class Repository<T>
    where T : MyEntityBase, INotifyPropertyChanged
{
    protected List<T> _data;
    public Repository(List<T> data)
    {
        this._data = data;
        foreach (var entity in this._data)
        {
            entity.PropertyChanged += new PropertyChangedEventHandler(entity_PropertyChanged);
        }
    }

    protected void entity_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        Console.WriteLine("HERE");
    }
}

Now I create a simple repository of type Employee, populate some data, and attempt to modify properties of the data. I would expect that the PropertyChanged event is raised since the Employee object has property-change notification built-in from the auto-generated DataContext. However, when I run the following code, I do not see HERE generated in the output anywhere:

var data = new List<Employee> {
    new Employee { FirstName = "Bob" },
    new Employee { FirstName = "Joe" },
};

var repo = new Repository<Employee>(data);

// This should fire the PropertyChanged event
data[0].FirstName = "John";

What am I doing wrong?

---

Update: If I change the line that subscribes to the event to the following:

(entity as Employee).PropertyChanged += ...

Then it works fine. However, T is already known to be Employee and entity is an instance of type Employee, so what’s the difference? Even if I make the event in MyEntityBase to be virtual, it still doesn’t work properly.

Answer 1

I have a workable solution implemented, so I will answer my own question. Since I already have a command-line tool FindAndReplaceText.exe that I use to do some customizations to the auto-generated MyDataContext.dbml file, I just added another call at the end where I modify all events in the generated MyDataContext class to include override. Coupled with making my base class use virtual in the definitions of the events, this solves the problem:

FindAndReplaceText.exe -c ^
    MyDataContext.cs ^
    "public event" ^
    "public override event"

Now the property changes notify properly in my test code.