Question

I want to bind a TextBox in the window to a property contained within a class that is a variable of the viewmodel and ensure that INotifyPropertyChanged’s PropertyChanged event propagates from the class to the parent.

Let me illustrate with an example:

(Window’s DataContext is set to an instance of ViewModel)

public class ViewModel {
    private OtherClass classInstance = new OtherClass();

    public int Attribute {
        get { return classInstance.Attribute; }
    }
}

public class OtherClass : INotifyPropertyChanged {
    private int _attribute;
    public int Attribute {
        get { return _attribute; }
        set { 
            _attribute = value;
            PropertyChanged("Attribute");
        }
    }
    ...
}

The problem in this example is that, when Attribute changes, the bound Textbox does not update the binding since I assume it’s listening to the ViewModel’s PropertyChanged event and not that of the instance of OtherClass.

Any ideas on how to remedy this situation? I was thinking about chaining OtherClass’s INotifyPropertyChanged to that of its parent, but there has to be a better way.

Answer 1

Why not bind directly to the class property instead of using a proxy?

public class ViewModel {
    private OtherClass classInstance = new OtherClass();

    public OtherClass MyOtherClass {
        get { return classInstance; }
    }
}

Then in your binding you can simply reference the property via the SubClass

{Binding MyOtherClass.Attribute}

---

A drop dead simple example, but it works!

The Code Behind:

public partial class MainWindow : Window {
   private readonly SomeClass _someClass = new SomeClass();

   public MainWindow() {
      InitializeComponent();
      DataContext = _someClass;
   }
}

public class SomeClass: INotifyPropertyChanged {      
   private readonly SomeSubClass _mySubClass = new SomeSubClass();

   public SomeSubClass MySubClass {
      get { return _mySubClass; }
   }

   private String _name;
   public String Name {
      get { return _name; }
      set {
         _name = value;
         OnPropertyChanged("Name");
      }
   }

   //Property Change Stuff
}

public class SomeSubClass : INotifyPropertyChanged {
   private String _name;
   public String Name {
      get {
         return _name;
      }
      set {
         _name = value;
         OnPropertyChanged("Name");
      }
   }

   //Property Change Stuff
}

The XAML:

<Window x:Class="JWC.Examples.WPF.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow">
    <StackPanel>
        <Label Content="Name" VerticalAlignment="Top" />
        <TextBox Text="{Binding Name}" />
        <Label Content="SubClass.Name" />
        <TextBox Text="{Binding MySubClass.Name}" />
        <Label Content="Bound to Name" />
        <TextBlock Text="{Binding Name}" />
        <Label Content="Bound to MySubClass.Name" />
        <TextBlock Text="{Binding MySubClass.Name}" />
    </StackPanel>
</Window>