Binding happened also by changing the values from the keyboard

Question

I have a combobox that is bind to the following list:

    private List<string> strList;
    public List<string> StrList
    {
        get { return strList; }
        set
        {
            strList = value;
            OnPropertyChanged("StrList");
        }
    }

The selected item is bind to the next object:

    private string str;
    public string Str
    {
        get { return str; }
        set
        {
            if (str != value)
            {
                str = value;
                OnPropertyChanged("Str");
            }
        }
    }

Following the combobox:

<ComboBox ItemsSource="{Binding StrList}"
          SelectedItem="{Binding Str,UpdateSourceTrigger=LostFocus}"
          Height="50" Width="200"/>

I want that the binding happens only on lost focus, and when changing the values ​​with the keys of the keyboard. Therefore UpdateSourceTrigger=LostFocus.

My question is how to do that binding happened also by changing the values ​​from the keyboard?

Answer 1

I created a behavior and in it I renewed the binding in a case of pressing the keys:

 public class KeysChangedBehavior : Behavior<ComboBox>
    {
        protected override void OnAttached()
        {
            this.AssociatedObject.AddHandler(ComboBox.KeyDownEvent,
          new RoutedEventHandler(this.OnKeysChanged));

            this.AssociatedObject.AddHandler(ComboBox.KeyUpEvent,
    new RoutedEventHandler(this.OnKeysChanged));
        }

        protected void OnKeysChanged(object sender, RoutedEventArgs e)
        {
            BindingExpression _binding = ((ComboBox)sender).GetBindingExpression(ComboBox.SelectedItemProperty);
            if (_binding != null)
                _binding.UpdateSource();
        }
    }

Here the combobox:

    <ComboBox ItemsSource="{Binding StrList}" SelectedItem="{Binding Str,UpdateSourceTrigger=LostFocus}" Height="50" Width="200">
        <i:Interaction.Behaviors>
            <KeysChangedBehavior/>
        </i:Interaction.Behaviors>
    </ComboBox>