Empty textbox bound with some decimal value - wpf

Question

I have a textbox bound to some decimal value. Now, if I type something in it like 100 and clear it completely (empty). I save the data and it saves 1 in decimal value. Similarly if I tried 200 and clear textbox it saves 2. Remember decimal value is not null. Any ideas?
<TextBox
Height="23"
VerticalAlignment="Center"
Text="{Binding Discount,Mode=TwoWay}"
MaxLength="50"
TabIndex="28"
Grid.Row="2"
Grid.Column="1"
local:FocusExtension.IsFocused=
"{Binding Path=IsDiscountFocused,Mode=TwoWay}"
Margin="5,0,0,0"/>

Answer 1

Since String.Empty cannot be converted into a decimal per default. The last valid value is kept in the property.
You should use a converter as below.
Wpf
<Window.Resources>
<local:ValueConverter x:Key="valueConverter" />
</Window.Resources>
<TextBox Text="{Binding Path=Value, Mode=TwoWay, Converter={StaticResource valueConverter}}" />
Converter:
public class ValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value is string && (string)value == "")
{
return 0;
}
return value;
}
}
Clr:
public decimal Value
{
get { return (decimal)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}

Answer 2

i assume that your Discount property in your viewmodel looks like:
public decimal Discount {get;set;}
if you use backspace and clear your textbox you get a binding exception because "" can not convertet to decimal. so the last number remains in your property. actually this should happen when using UpdateSourceTrigger=Propertychanged. but nevertheless you can try using decimal?. if this not help you can also add a converter to convert the "" to a value your viewmodel can handle.
EDIT: i did not see you last comment. but in the case you want a 0 for an empty textbox, just use a converter to return 0 when "" is the input.