Silverlight 4 TextBox not validating

Question

We have a SL 4 application utilizing an MVVM architecture and pretty clean data binding between objects and UI controls. We have created a custom ValidationAttribute that we use to decorate our domain classes and to provide field level validation based on a data store. If we utilize these custom validation attributes and manually validate our classes using the Validator class like this:

        bool _isValid = Validator.TryValidateObject(this.DataContext, new ValidationContext(this.DataContext,null,null), results,true);

then the custom validation attributes are utilized and everything works fine.

Our issue is that, when simply entering data into a textbox bound to a field decorated with one of these validation attributes we do not see immediate validation feedback (via the default red border and tooltip styling of the tool box).

A sample XAML snippet of a control not validating upon lost focus is:

        <TextBox Text="{Binding AssetID,Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnDataErrors=true}"></TextBox>

Any suggestions on what we are overlooking or what we can do to force SL to validate text boxes upon lost focus and not wait until a page level save is done (at which point we just validate with the Validator class)?

Answer 1

You have to validate the value in the property setter of the property you're bound to.

You can see what I mean in this post. http://msdn.microsoft.com/en-us/magazine/ee335695.aspx

Can you post the property you're binding to, specifically the setter code?