Question

In my .NET 4.0 project I’ve got an object that has public fields and this object neither implements INotifyPropertyChanged nor inherits DependencyObject, and it will never do. However, I need a mechanism to “bind” to fields of this object in my WPF control. I know I can’t do it directly as binding requires a dependency property (or at least, properties and notifying property changes), so what can I do to implement the binding functionality I need. I’ve tried something like this in my WPF control:

    void FirePropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public float Friction
    {
        get
        {
            if (CurrentObject != null)
            {
                return CurrentObject.Friction;
            }
            else
            {
                return 0.0f;
            }
        }
        set
        {
            if (CurrentObject != null)
            {
                CurrentObject.Friction = value;
                FirePropertyChanged("Friction");
            }
        }
    }

    public PlatformObjectTemplate CurrentObject
    {
        get
        {
            return GetValue(CurrentObjectProperty) as PlatformObjectTemplate;
        }
        set
        {
            SetValue(CurrentObjectProperty, value);
            FirePropertyChanged("Friction");
            FirePropertyChanged("CurrentObject");
            BindShapes();
            IntersectionComboBox.SelectedItem = CurrentObject.IntersectionStaticMethod;
        }
    }

    public static readonly DependencyProperty CurrentObjectProperty = DependencyProperty.Register("CurrentObject", typeof(PlatformObjectTemplate), typeof(PlatformStaticObjectPropertyEditor), new PropertyMetadata(null));

My WPF control implements INotifyPropertyChanged, and my PlatformObjectTemplate does not have properties, just public fields like Friction. I need to bind to my object in XAML as such:

(in my control): //DoubleUpDown is from the WPF toolkit.

<tk:DoubleUpDown Margin="91,10,7,0" Name="doubleUpDown1" VerticalAlignment="Top" Value="{Binding Friction, ElementName=window, FallbackValue=0}" />

(in my main window):

<my:PlatformStaticObjectPropertyEditor x:Name="platformStaticObjectPropertyEditor1" CurrentObject="{Binding CurrentObject, ElementName=window}" />

I put a breakpoint in the getter of Friction property, and it tries to bind before the CurrentObject is bound, and because it is null, I can’t read the correct friction value from the object. I’ve tried to fire Friction property changed in the setter of the CurrentObject, to populate the Friction when CurrentObject gets set, but that doesn’t work either.

Ok, here are two requirements:

PlatformObjectTemplate will not use properties. It will have public fields.
I need a declarative way of binding as usual, just as I used in the XAML above.

I probably have got things over-complicated, and I must be missing some stuff. What is the most “correct” and “declarative” way of doing this right, within the constraints of my requirements just above?

Thanks,
Can.

Answer 1

object neither implements INotifyPropertyChanged nor inherits DependencyObject, and it will never. However, I need a mechanism to "bind" to fields of this object in my WPF control

poyra, I have this same situation. Because one cannot bind to instance fields, your best option is to create wrapper classes which implement INotifyPropertyChanged.