Attached Property on TextBox WPF

Question

My problem is simple I have a textbox in WPF where you can type a number. I want three things when I press specific keys :

• Enter : the value is sent
• Up : the value is increased then sent
• Down : the value is decreased then sent

I have made 3 attached properties but it works only for the Key Enter.

<TextBox Margin="5,0"  hlp:TextboxBehaviors.KeyToValid="Enter" hlp:Decrease.KeyToDecrease="Down" hlp:Increase.KeyToIncrease="Up"  Text="{Binding Target, Mode=TwoWay, UpdateSourceTrigger=Explicit, Converter={StaticResource kiloConverter}, ValidatesOnNotifyDataErrors=True, ValidatesOnExceptions=True}" />

The code of the class :

public static class Decrease
{
    private static Key TriggeredKey = Key.Down;
    public static Key GetKeyToDecrease(DependencyObject obj)
    {
        return (Key)obj.GetValue(KeyToDecreaseProperty);
    }

    /// <summary>
    /// Sert uniquement à s'attacher à la TextBox (une seule fois à l'init de l'interface)
    /// </summary>
    public static void SetKeyToDecrease(DependencyObject obj, Key value)
    {
        var tb = obj as TextBox;
        if (tb != null)
            tb.KeyDown += OnKeyDown;
    }

    /// <summary>
    /// Evenement classique
    /// </summary>
    private static void OnKeyDown(object sender, KeyEventArgs e)
    {
        var tbCurrent = sender as TextBox;
        int selectedpos;

        if (tbCurrent != null && e.Key == TriggeredKey)
        {
            if (tbCurrent.SelectionStart > 0)
            {
                if (!tbCurrent.Text.Contains("."))
                {
                    int exp = tbCurrent.Text.Length - tbCurrent.SelectionStart;
                    tbCurrent.Text = (Convert.ToDouble(tbCurrent.Text) - Math.Pow(10, exp)).ToString();
                    selectedpos = tbCurrent.Text.Length - exp;
                }
                else
                {
                    int exp;
                    if (tbCurrent.SelectionStart > tbCurrent.Text.IndexOf('.') + 1)
                    {
                        exp = tbCurrent.Text.IndexOf('.') - tbCurrent.SelectionStart + 1;
                    }
                    else if (tbCurrent.SelectionStart < tbCurrent.Text.IndexOf('.') + 1)
                    {
                        exp = tbCurrent.Text.IndexOf('.') - tbCurrent.SelectionStart;
                    }
                    else
                    {
                        return;
                    }

                    tbCurrent.Text = (Convert.ToDouble(tbCurrent.Text) - Math.Pow(10, exp)).ToString("0.00");

                    if (exp < 0)
                    {
                        selectedpos = tbCurrent.Text.IndexOf('.') - exp + 1;
                    }
                    else
                    {
                        if (tbCurrent.Text.IndexOf('.') - exp < 0)
                        {
                            selectedpos = 0;
                        }
                        else
                        {
                            selectedpos = tbCurrent.Text.IndexOf('.') - exp;
                        }
                    }
                }

                BindingExpression binding = tbCurrent.GetBindingExpression(TextBox.TextProperty);
                if (binding != null)
                {
                    binding.UpdateSource();
                }

                tbCurrent.SelectionLength = 0;
                if (selectedpos >= 0)
                {
                    tbCurrent.SelectionStart = selectedpos;
                }
                else
                {
                    tbCurrent.SelectionStart = 0;
                }
            }
        }
    }

    // Using a DependencyProperty as the backing store for KeyToValid.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty KeyToDecreaseProperty =
        DependencyProperty.RegisterAttached("KeyToDecrease", typeof(Key), typeof(TextBox), new PropertyMetadata(TriggeredKey));

}

This the code for the Decrease attached behavior the two others are designed in the same way.

The decrease and the increase don't trigger the event ! The enter does...

Answer 1

The decrease and the increase don't trigger the event ! The enter does...

Handle the Preview KeyDown event:

public static void SetKeyToDecrease(DependencyObject obj, Key value)
{
    var tb = obj as TextBox;
    if (tb != null)
        tb.PreviewKeyDown += OnKeyDown;
}

The TextBox control handles and "swallows" certain key presses on its own. That's why the KeyDown event isn't fired in your behaviour.