WPF textbox that only updates binding when enter is pressed

Question

Hi, all. I have a usercontrol "NumericTextBox" that only allows numeric entries. I need to exhibit another specialized behaviour, that is, I need it to be able to bind it to a VM value OneWayToSource and only have the VM value update when I press enter while focusing the textbox. I already have the an EnterPressed event that fires when I press the key, I'm just having a hard time figuring out a way to cause that action to update the binding...

Answer 1

In your binding expression, set the UpdateSourceTrigger to Explicit.

Text="{Binding ..., UpdateSourceTrigger=Explicit}"

Then, when handling the EnterPressed event, call UpdateSource on the binding expression, this will push the value from the textbox to the actual bound property.

BindingExpression exp = textBox.GetBindingExpression(TextBox.TextProperty);
exp.UpdateSource();

Answer 2

If you are using MVVM you can use a combination of decastelijau's approach along with a custom attached property that calls UpdateSource on the textbox when PreviewKeyUp.

public static readonly DependencyProperty UpdateSourceOnKey = DependencyProperty.RegisterAttached(
  "UpdateSourceOnKey",
  typeof(Key),
  typeof(TextBox),
  new FrameworkPropertyMetadata(false)
);
public static void SetUpdateSourceOnKey(UIElement element, Key value)
{

  //TODO: wire up specified key down event handler here
  element.SetValue(UpdateSourceOnKey, value);

}
public static Boolean GetUpdateSourceOnKey(UIElement element)
{
  return (Key)element.GetValue(UpdateSourceOnKey);
}

Then you can do:

<TextBox myprops:UpdaterProps.UpdateSourceOnKey="Enter" ... />