Bind TextBox.TextProperty to a property of type Binding from the Model

Question

I've got a list of command buttons (with input) I want to bind with the model. The thing is I want the textbox in the button to bind to somewhere (see viewmodel).

The following code is what I tried and failed. Is it (even) possible to set binding on the model then bind this to a control?

Or in other words am I trying to do something the stupid way?

View:

<ToolBar Grid.Row="1" Grid.ColumnSpan="2" Grid.Column="0" ItemsSource="{Binding SelectedTab.Commands}" Height="34">
    <ToolBar.Resources>
        <DataTemplate DataType="{x:Type model:ZoekCommandButtons}">
            <Button Command="{Binding Command}" ToolTip="{Binding Tooltip}" Style="{StaticResource {x:Static ToolBar.ButtonStyleKey}}">
                <StackPanel Orientation="Horizontal">
                    <Image Source="{Binding Image, Converter={StaticResource ImageConv}}" Height="16" Width="16"></Image>
                    **<TextBox Width="100" Text="{Binding Text}">**
                        <TextBox.InputBindings>
                            <KeyBinding Gesture="Enter" Command="{Binding Command}"></KeyBinding>
                        </TextBox.InputBindings>
                    </TextBox>
                </StackPanel>
            </Button>
        </DataTemplate>
    </ToolBar.Resources>
</ToolBar>

Model:

    public class ZoekCommandButtons : BaseModel, ICommandItem
    {
        private string _header;
        private string _image;
        private bool _isEnabled;
        private Visibility _isVisible;
        private ICommand _command;
        private string _tooltip;
        private Binding _text;


        public Binding Text
        {
            get { return _text; }
            set { _text = value; OnPropertyChanged("Text"); }
        }
(etc)

Viewmodel:

    Commands.Add(new ZoekCommandButtons()
    {
        Image = "search.png",
        IsEnabled = true,
        **Text = new Binding { RelativeSource = new RelativeSource(RelativeSourceMode.FindAncestor, typeof(UserControl), 1), Path = new PropertyPath("FilterText") },**
        Command = FilterCommand,
        Tooltip = "Zoeken",
        Header = "Zoeken"
    });

Answer 1

First off, I would not recommend exposing Binding as a ViewModel property; in this particular case, it sounds more to me like you have nested ViewModels, and that approach would be far more suitable - that is, you have a "MamaViewModel" that has your "Commands" property, which is in turn a collection of "CommandButtonViewModels"...

Ok, That said...you can do this, although I must reiterate that you probably should not; what you're missing is "something to evaluate the Binding on" to provide a value. Here's a class that gives you that:

public static class BindingEvaluator
{
    // need a DP to set the binding to
    private static readonly DependencyProperty PlaceholderProperty = 
        DependencyProperty.RegisterAttached("Placeholder", typeof(object), typeof(DependencyObject), new UIPropertyMetadata(null));

    // Evaluate a binding by attaching it to a dummy object/property and evaluating the property value
    public static object Evaluate(Binding binding)
    {
        var throwaway = new DependencyObject();
        BindingOperations.SetBinding(throwaway, PlaceholderProperty, binding);
        var retVal = throwaway.GetValue(PlaceholderProperty);
        return retVal;
    }
}

That, combined with a ViewModel definition something like:

public class DontDoThisViewModel
{
    public Binding TextBinding {get; set;}
    public string Text 
    {
        get 
        {
            return BindingEvaluator.Evaluate(TextBinding) as string;
        }
    }
}

Should work...here's a test app I threw together in LINQPad:

void Main()
{
    var wnd = new Window() { Title = "My window" };
    var text = new TextBlock();
    text.Text = "Hopefully this shows the window title...";
    text.SetBinding(TextBlock.TextProperty, new Binding("Text"));
    wnd.Content = text;
    var vm = new ViewModel();
    var vmBinding = new Binding("Title");
    vmBinding.Source = wnd;
    vm.TextBinding = vmBinding;
    wnd.DataContext = vm;
    wnd.Show();
}

AGAIN, I must strongly recommend you NOT do this...but I was curious, so I had to come up with a way. ;)

Answer 2

Ok. I wasn't thinking straight.

Changed the Text property in the Model to string and handled the command with this property.

(although it would be nice to set binding on the model somehow...)