Question

<Setter Property="IsChecked">
    <Setter.Value>
        <MultiBinding>
            <!-- Get value for property -->
            <Binding Path="IsPressed" RelativeSource="{RelativeSource Self}" Mode="OneWay"/>
            <!-- Set value to ViewModel's property -->
            <Binding Path="Shift" Mode="OneWayToSource"/>
        </MultiBinding>
    </Setter.Value>
</Setter>

I need to use 2 bindings for property: one to get value for property and one to set value to ViewModel’s property.
How I can realize this scenario?

Answer 1

You can create a couple of attached properties. One will be the target of your binding, and second will contain binding for your proxy. Example:

Then in ProxySource OnChange implementation you will get TextBox as UIElement, there you can read value from ProxySource and write it to ProxyTarget.
This is not a very clean aproach, but it should work.
If you can’t get it working, I can write a complete sample later.
Ok, I’ve implemented everything, here’s complete source:

public class ViewModel : ViewModelBase
{
    string sourceText;
    public string SourceText
    {
        get { return sourceText; }
        set
        {
            if (sourceText == value) return;
            sourceText = value;
            System.Diagnostics.Debug.WriteLine("SourceText:" + value);
            RaisePropertyChanged("SourceText");
        }
    }

    string targetText;
    public string TargetText
    {
        get { return targetText; }
        set
        {
            if (targetText == value) return;
            targetText = value;
            System.Diagnostics.Debug.WriteLine("TargetText:" + value);
            RaisePropertyChanged("TargetText");
        }
    }
}

public static class AttachedPropertiesHost
{
    public static object GetProxySource(DependencyObject obj)
    {
        return obj.GetValue(ProxySourceProperty);
    }

    public static void SetProxySource(DependencyObject obj, object value)
    {
        obj.SetValue(ProxySourceProperty, value);
    }

    public static readonly DependencyProperty ProxySourceProperty =
            DependencyProperty.RegisterAttached(
                "ProxySource", typeof(object), typeof(AttachedPropertiesHost),
                new UIPropertyMetadata(null, ProxySourcePropertyPropertyChanged)
            );

    private static void ProxySourcePropertyPropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        dependencyObject.Dispatcher.BeginInvoke(
                new { Dp = dependencyObject, NewValue = e.NewValue },
                args => SetProxyTarget(args.Dp, args.NewValue)
            );
    }

    public static object GetProxyTarget(DependencyObject obj)
    {
        return obj.GetValue(ProxyTargetProperty);
    }

    public static void SetProxyTarget(DependencyObject obj, object value)
    {
        obj.SetValue(ProxyTargetProperty, value);
    }

    public static readonly DependencyProperty ProxyTargetProperty =
            DependencyProperty.RegisterAttached("ProxyTarget", typeof(object), typeof(AttachedPropertiesHost));
    }

<TextBox Text="{Binding SourceText, UpdateSourceTrigger=PropertyChanged}" 
             WpfDataGridLayout:AttachedPropertiesHost.ProxySource="{Binding RelativeSource={RelativeSource Self}, Path=Text, UpdateSourceTrigger=PropertyChanged}"
             WpfDataGridLayout:AttachedPropertiesHost.ProxyTarget="{Binding TargetText, Mode=OneWayToSource}"
             />

And the output from console while editing textbox:
SourceText:f
TargetText:f
SourceText:fh
TargetText:fh
SourceText:fhh
TargetText:fhh