Question

Is there a way to get a TextBox in Windows Phone 7 to update the Binding as the user types each letter rather than after losing focus?

Like the following WPF TextBox would do:

<TextBox Text="{Binding Path=TextProperty, UpdateSourceTrigger=PropertyChanged}"/>

Answer 1

Silverlight for WP7 does not support the syntax you’ve listed. Do the following instead:

<TextBox TextChanged="OnTextBoxTextChanged"
         Text="{Binding MyText, Mode=TwoWay,
                UpdateSourceTrigger=Explicit}" />

UpdateSourceTrigger = Explicit is a smart bonus here. What is it? Explicit: Updates the binding source only when you call the UpdateSource method. It saves you one extra binding set when the user leaves the TextBox.

In C#:

private void OnTextBoxTextChanged( object sender, TextChangedEventArgs e )
{
  TextBox textBox = sender as TextBox;
  // Update the binding source
  BindingExpression bindingExpr = textBox.GetBindingExpression( TextBox.TextProperty );
  bindingExpr.UpdateSource();
}