Question

I am attempting to bind my ViewModel’s IsInInputMode property to a Dependency Property in a UserControl. I am setting the UserControl’s DataContext to an instance of my ViewModel and all my XAML based bindings are working correctly. I need a code-behind solution to create this binding. I’ve tried a few things (at the bottom of the post) which have not worked.

I’m not getting any exceptions logged to the Output window either, which is where I’ve been told to look for Binding based exceptions.

I asked this similar question, on binding a Dependency Property in a UserControl through XAML — I was told this is not possible, so I’m looking for a code-behind solution.

The ViewModel looks like this:

class AddClientViewModel : ViewModelBase
{
    private Boolean _isInInputMode;
    public Boolean IsInInputMode
    {
        get { return _isInInputMode; }
        set
        {
            _isInInputMode = value;
            OnPropertyChanged("IsInInputMode");
        }
    }

    public ICommand Cancel
    {
        get { return new RelayCommand(parm => { IsInInputMode = false; }); }
    }
}

The Cancel command is successfully being data bound to a Button’s Command through XAML.

The Dependency Property in the UserControl looks like this:

    public bool IsInInputMode
    {
        get { return (bool)GetValue(IsInInputModeProperty); }
        set { SetValue(IsInInputModeProperty, value); }
    }
    public static readonly DependencyProperty IsInInputModeProperty =
        DependencyProperty.Register("IsInInputMode", typeof(bool), typeof(AddClientView), new UIPropertyMetadata(new PropertyChangedCallback(_OnIsInInputModePropertyChanged)));

    private static void _OnIsInInputModePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var mycontrol = d as AddClientView;

        bool oldValue = (bool)e.OldValue;
        bool newValue = (bool)e.NewValue;

        if (null != mycontrol && oldValue != newValue)
        {
            mycontrol._OnIsInInputModeChanged(oldValue, newValue);
        }
    }

    private void _OnIsInInputModeChanged(bool oldValue, bool newValue)
    {
        if (newValue)
        {
            VisualStateManager.GoToState(this, "InputState", false);
        }
        else
        {
            VisualStateManager.GoToState(this, "HiddenState", false);
        }
    }

The Binding in the Constructor of my UserControl has had a few iterations.

First Try:

    public AddClientView()
    {
        InitializeComponent();
        SetBinding(IsInInputModeProperty, "IsInInputMode");
    }

Second Try:

    public AddClientView()
    {
        InitializeComponent();

        var b = new Binding();
        b.Source = this.DataContext;
        b.Path = new PropertyPath("IsInInputMode");
        b.Mode = BindingMode.TwoWay;
        b.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
        BindingOperations.SetBinding(this, IsInInputModeProperty, b);
    }

Neither of these “fail” with a compiler or runtime error; but when the IsInInputMode property changes in the ViewModel, the Dependency Property never updates, and the two even handlers there are never called.

As an additional note, the ViewModel has a few ICommand properties, which are being successfully bound to buttons in the UserControl via XAML — so I know the DataContext binding correctly.

Answer 1

Turns out it was a PEBKEC issue — I had a default value set somewhere, so OnNotifyPropertyChanged never got called, as such it appeared that the binding was broken.

I bound my boolean to a checkbox on the View, and using the UI control to change the value forced my animations to change, the correct code-behind binding was my first try:

SetBinding(IsInInputModeProperty, "IsInInputMode");