WPF textbox that only updates binding when enter is pressed - wpf

Question

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

Here is a complete version of the idea provided by Anderson Imes:
public static readonly DependencyProperty UpdateSourceOnKeyProperty =
DependencyProperty.RegisterAttached("UpdateSourceOnKey",
typeof(Key), typeof(TextBox), new FrameworkPropertyMetadata(Key.None));
public static void SetUpdateSourceOnKey(UIElement element, Key value) {
element.PreviewKeyUp += TextBoxKeyUp;
element.SetValue(UpdateSourceOnKeyProperty, value);
}
static void TextBoxKeyUp(object sender, KeyEventArgs e) {
var textBox = sender as TextBox;
if (textBox == null) return;
var propertyValue = (Key)textBox.GetValue(UpdateSourceOnKeyProperty);
if (e.Key != propertyValue) return;
var bindingExpression = textBox.GetBindingExpression(TextBox.TextProperty);
if (bindingExpression != null) bindingExpression.UpdateSource();
}
public static Key GetUpdateSourceOnKey(UIElement element) {
return (Key)element.GetValue(UpdateSourceOnKeyProperty);
}

Answer 3

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" ... />