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Posted 6 Jul 2010

Updating Source on PropertyChanged on Silverlight

, 6 Jul 2010
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A simple dependency property that allows you to update a property on PropertyChanged.


Don't you miss the "UpdateSourceTrigger=PropertyChanged" on a Binding expression on Silverlight? Well, me too, and since I don't like the idea of having a hidden control to change focus on every TextChange of my TextBoxes, I tried to make a more elegant solution for the problem.


In both WPF and Silverlight, when we create a BindingExpression, you can define a UpdateSourceTrigger property of the Binding. But, there is a huge difference between them, Silverlight has only the Default mode (LostFocus) and Explicit, so we are missing PropertyChanged that in some cases makes our life way easier.

Using the Code

The code is fairly simple. It is only one AttachedProperty that will handle the TextChanged for you and will update the BindingSource if the BindingExpression of the TextProperty exists.

This was only implemented in the TextBox because there is no need to change the other input controls over the fact that LostFocus works perfect for them (like ComboBoxes, CheckBoxes, RadioButtons).

So, we define an AttachedProperty that shouldn't be a problem to any Silverlight developer:

public static bool GetUpdateOnPropertyChanged(DependencyObject obj)
    return (bool)obj.GetValue(UpdateOnPropertyChangedProperty);

public static void SetUpdateOnPropertyChanged(DependencyObject obj, bool value)
    obj.SetValue(UpdateOnPropertyChangedProperty, value);

public static readonly DependencyProperty UpdateOnPropertyChangedProperty =
        new PropertyMetadata(
            new PropertyChangedCallback(

Then we define the UpdateOnPropertyChangedPropertyCallback:

static void UpdateOnPropertyChangedPropertyCallback(
    DependencyObject sender, DependencyPropertyChangedEventArgs e)
    if (sender is TextBox)
        TextBox txt = sender as TextBox;
        txt.TextChanged += new TextChangedEventHandler(txt_TextChanged);

static void txt_TextChanged(object sender, TextChangedEventArgs e)
    TextBox txt = sender as TextBox;

    var bindingExpression = txt.GetBindingExpression(TextBox.TextProperty);
    if (bindingExpression != null)

Then, for using this, just add to your UserControl the proper XML namespace like:

<UserControl x:class="UpdateSourceTrigger.MainPage"







And finally, add the Attached Property to the TextBox as follows:


    Text="{Binding Context.FirstName, Mode=TwoWay}" 






The End

Hope this can make things easier to you, as it did to me.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Raul Mainardi Neto
Brazil Brazil
Senior .NET Architect from Brazil.

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Comments and Discussions

QuestionUpdateSourceManager weird bug on a deployed View Pin
Mycroft Holmes28-Aug-12 15:54
memberMycroft Holmes28-Aug-12 15:54 
GeneralMy vote of 4 Pin
Albert van Peppen27-Jul-12 1:11
memberAlbert van Peppen27-Jul-12 1:11 
GeneralMy vote of 5 Pin
Mycroft Holmes12-Jul-12 19:19
memberMycroft Holmes12-Jul-12 19:19 
SuggestionCan add a notifier dynamically Pin
chprogmer16-Nov-11 23:52
memberchprogmer16-Nov-11 23:52 
GeneralMy vote of 5 Pin
Duke Carey18-May-11 3:29
memberDuke Carey18-May-11 3:29 
GeneralGreat! Pin
Marcelo Ricardo de Oliveira12-Jul-10 7:57
memberMarcelo Ricardo de Oliveira12-Jul-10 7:57 
GeneralRe: Great! Pin
Raul Mainardi Neto12-Jul-10 8:01
memberRaul Mainardi Neto12-Jul-10 8:01 
GeneralCool Pin
Alan Beasley8-Jul-10 23:16
memberAlan Beasley8-Jul-10 23:16 
GeneralRe: Cool Pin
Raul Mainardi Neto9-Jul-10 16:14
memberRaul Mainardi Neto9-Jul-10 16:14 
GeneralCool, makes sense to me. SL really is limited Pin
Sacha Barber8-Jul-10 5:51
mvpSacha Barber8-Jul-10 5:51 
GeneralRe: Cool, makes sense to me. SL really is limited Pin
Raul Mainardi Neto8-Jul-10 6:01
memberRaul Mainardi Neto8-Jul-10 6:01 
Yep... Silverlight is cool, but there are a LOT of limitations, hoping for the best in version 5. But since I am currently working with Silverlight only at work, I have been finding some cool stuff there also... great for media...

Best regards dude.
GeneralRe: Cool, makes sense to me. SL really is limited Pin
Alan Beasley8-Jul-10 23:12
memberAlan Beasley8-Jul-10 23:12 
GeneralRe: Cool, makes sense to me. SL really is limited Pin
Sacha Barber9-Jul-10 0:01
mvpSacha Barber9-Jul-10 0:01 

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