INotifyPropertyChanged: Notify another class

Question

I have a class (let's call it MyContainerClass)that is a container for several other classes (let's call them ClassA to ClassF). ClassA to ClassF inherit the same base class (let's call it MyBaseClass). In MyBaseClass I have an int property with the name Count, which ClassA to ClassF inherit. I also have an int property with the same name in MyContainerClass which is the sum of ClassA to ClassF.

Then I have a datagrid, and each row has one object of MyContainerClass. The columns of the grid show ClassA to ClassF. The last column in the grid shows a total (that is it is bound the Count property of MyContainerClass). Now I want that the total in the last column updates as soon as I change the Count property in any class in the A-F range. I implemented INotifyPropertyChanged in MyBaseClass and it does fire when I change the Count property in ClassA to ClassF. But the last column in my datagrid remains the same. Any clues?

EDIT: I have created a class diagram.

The getCount() method returns objA.Count+objB.Count+...+objF.Count and is returned by the Count property in the MyContainerClass. The question is: if I update objA.Count I want the GUI (that is the column in my datagrid) to display the updated sum.

Answer 1

Just implementing INotifyPropertyChanged is not enough for an automatic update. The MyContainerClass object needs to "subscribe" to the change notifications of the MyBaseClass objects in the other columns. One way you can handle this is by adding a method like the following to the MyContainerClass:

void SubscribeToCount(MyBaseClass item)
{
    item.PropertyChanged += (s,e) => 
        this.Sum += (e.NewValue - e.OldValue); 
}

And you call this method for all the objects in the other columns. (It's not clear from the question but I assume there is a wrapper class that includes instances of MyClassA-F and MyContainerClass, which you bind the datagrid to a collection of this wrapper class).

Answer 2

Okay, here is what I did after staring at Eren's solution for a while: I also implemented the INotifyPropertyChanged for the container class and registered the PropertyChanged event for each object.

objA.PropertyChanged += updateCount;
objB.PropertyChanged += updateCount;
objC.PropertyChanged += updateCount;

...and so on. Then I added the following method

private void updateCount(object sender, PropertyChangedEventArgs e)
{
    OnPropertyChanged("Count");
}

Now I have the behavior that I want.