INotifyPropertyChanged: Notify another class

data-binding, datagrid, inotifypropertychanged, wpf

Solution

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).

Problem

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.

Original source