Best way to notify property change when field is depending on another

Question

What is the best way in c# to notify property changed on an item\'s field without set but get depends on other fields ?

For example :

Answer 1

As far as I know, there is not built in method for that. I usually do like this:

public class Foo : INotifyPropertyChanged
{
    private Bar _bar1;

    public Bar Item
    {
        get { return _bar1; }
        set 
        { 
             SetField(ref _bar1, value); 
             ItemChanged();
        }
    }

    public string MyString
    {
        get { return _bar1.Item; }
    }

    private void ItemChanged()
    {
        OnPropertyChanged("MyString");
    }
}

public class Bar
{
    public string Item { get; set; }
}

You don't have the notifying logic inside of the property this way. It is more maintainable in my opinion this way and it is clear what the method does.

Also, I prefer to use this method I found somewhere on SO instead of the hardcoded name in the class (if the name of the property changes, it breaks).

OnPropertyChanged("MyString"); becomes OnPropertyChanged(GetPropertyName(() => MyString));

where GetPropertyName is:

public static string GetPropertyName(Expression> propertyLambda)
{
    if (propertyLambda == null) throw new ArgumentNullException("propertyLambda");

    var me = propertyLambda.Body as MemberExpression;

    if (me == null)
    {
        throw new ArgumentException("You must pass a lambda of the form: '() => Class.Property' or '() => object.Property'");
    }

    return me.Member.Name;
}

After this, every time I change the property as the name, I will have to rename the property everywhere I have GetPropertyName instead of searching for the hardcoded string values.

I'm also curious about a built-in way to do the dependency, so I'm putting a favorite in there :)