Try to resolve that on ViewModel level. That it:
public class FormattedDecimalViewModel : INotifyPropertyChanged
{
private readonly string _format;
public FormattedDecimalViewModel()
: this("F2")
{
}
public FormattedDecimalViewModel(string format)
{
_format = format;
}
private string _someDecimalAsString;
// String value that will be displayed on the view.
// Bind this property to your control
public string SomeDecimalAsString
{
get
{
return _someDecimalAsString;
}
set
{
_someDecimalAsString = value;
RaisePropertyChanged("SomeDecimalAsString");
RaisePropertyChanged("SomeDecimal");
}
}
// Converts user input to decimal or initializes view model
public decimal SomeDecimal
{
get
{
return decimal.Parse(_someDecimalAsString);
}
set
{
SomeDecimalAsString = value.ToString(_format);
}
}
// Applies format forcibly
public void ApplyFormat()
{
SomeDecimalAsString = SomeDecimal.ToString(_format);
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
SAMPLE
Xaml:
<TextBox x:Name="tb" Text="{Binding Path=SomeDecimalAsString, UpdateSourceTrigger=PropertyChanged}" />
Code behind:
public MainWindow()
{
InitializeComponent();
FormattedDecimalViewModel formattedDecimalViewModel = new FormattedDecimalViewModel { SomeDecimal = (decimal)2.50 };
tb.LostFocus += (s, e) => formattedDecimalViewModel.ApplyFormat(); // when user finishes to type, will apply formatting
DataContext = formattedDecimalViewModel;
}