Implementing INotifyPropertyChanged for nested properties

Question

I have a Person class:

public class Person : INotifyPropertyChanged
{
     private string _name;
     public string Name{
     get { return _name; }
     set {
           if ( _name != value ) {
             _name = value;
             OnPropertyChanged( "Name" );
           }
     }

     private Address _primaryAddress;
     public Address PrimaryAddress {
     get { return _primaryAddress; }
     set {
           if ( _primaryAddress != value ) {
             _primaryAddress = value;
             OnPropertyChanged( "PrimaryAddress" );
           }
     }

     //OnPropertyChanged code goes here
}

I have an Address class:

public class Address : INotifyPropertyChanged
{
     private string _streetone;
     public string StreetOne{
     get { return _streetone; }
     set {
           if ( _streetone != value ) {
             _streetone = value;
             OnPropertyChanged( "StreetOne" );
           }
     }

     //Other fields here

     //OnPropertyChanged code goes here
}

I have a ViewModel:

public class MyViewModel
{
   //constructor and other stuff here

     private Person _person;
     public Person Person{
     get { return _person; }
     set {
           if ( _person != value ) {
             _person = value;
             OnPropertyChanged( "Person" );
           }
     }

}

I have a View which has the following lines:

<TextBox  Text="{Binding Person.Name, Mode=TwoWay,   
    UpdateSourceTrigger=PropertyChanged />

<TextBox  Text="{Binding Person.Address.StreetOne, Mode=TwoWay,   
    UpdateSourceTrigger=PropertyChanged />

Both values show up in the text box ok when the view loads.

Changes to the first text box will fire OnPropertyChanged( "Person" ) in MyViewModel. Great.

Changes to the second text box ("Person.Address.StreetOne") does NOT fire OnPropertyChanged( "Person" ) inside MyViewModel. Meaning it doesn't call the Person object's SET method. Not great. Interestingly the SET method of StreetOne inside the Address class is called.

How do I get the SET method of the Person object inside the ViewModel to be called when Person.Address.StreetOne is changed???

Do I need to flatten my data so SteetOne is inside Person and not Address??

Thanks!

Answer 1

While adding 'pass-through' properties to your ViewModel is a fine solution, it can quickly become untenable. The standard alternative is to propagate changes as below:

  public Address PrimaryAddress {
     get => _primaryAddress;
     set {
           if ( _primaryAddress != value ) 
           {
             //Clean-up old event handler:
             if(_primaryAddress != null)
               _primaryAddress.PropertyChanged -= AddressChanged;

             _primaryAddress = value;

             if (_primaryAddress != null)
               _primaryAddress.PropertyChanged += AddressChanged;

             OnPropertyChanged( "PrimaryAddress" );
           }

           void AddressChanged(object sender, PropertyChangedEventArgs args) 
               => OnPropertyChanged("PrimaryAddress");
        }
  }

Now change notifications are propagated from Address to person.

Edit: Moved handler to c# 7 local function.