WPF Data Binding and Validation Rules Best Practices

Question

I have a very simple WPF application in which I am using data binding to allow editing of some custom CLR objects  I am now wanting to put some input validation in when the user clicks save  However  all the WPF books I have read don t really devote any space to this issue  I see that you can create custom ValidationRules  but I am wondering if this would be overkill for my needs   So my question is this  is there a good sample application or article somewhere that demonstrates best practice for validating user input in WPF

User · Accepted Answer

I think the new preferred way might be to use IDataErrorInfo  Read more here

User · Answer

From MS s Patterns  amp  Practices documentation      Data Validation and Error Reporting      Your view model or model will often be   required to perform data validation   and to signal any data validation   errors to the view so that the user   can act to correct them       Silverlight and WPF provide support   for managing data validation errors   that occur when changing individual   properties that are bound to controls   in the view  For single properties   that are data-bound to a control  the   view model or model can signal a data   validation error within the property   setter by rejecting an incoming bad   value and throwing an exception  If   the ValidatesOnExceptions property on   the data binding is true  the data   binding engine in WPF and Silverlight   will handle the exception and display   a visual cue to the user that there is   a data validation error       However  throwing exceptions with   properties in this way should be   avoided where possible  An alternative   approach is to implement the   IDataErrorInfo or INotifyDataErrorInfo   interfaces on your view model or model   classes  These interfaces allow your   view model or model to perform data   validation for one or more property   values and to return an error message   to the view so that the user can be   notified of the error    The documentation goes on to explain how to implement IDataErrorInfo and INotifyDataErrorInfo

User · Answer

personaly  i m using exceptions to handle validation  it requires following steps    in your data binding expression  you need to add  ValidatesOnException True  in you data object you are binding to  you need to add DependencyPropertyChanged handler where you check if new value fulfills your conditions - if not - you restore to the object old value  if you need to  and you throw exception   in your control template you use for displaying invalid value in the control  you can access Error collection and display exception message    the trick here  is to bind only to objects which derive from DependencyObject  simple implementation of INotifyPropertyChanged wouldn t work - there is a bug in the framework  which prevents you from accessing error collection

User · Answer

If your business class is directly used by your UI is preferrable to use IDataErrorInfo because it put logic closer to their owner   If your business class is a stub class created by a reference to an WCF XmlWeb service then you can not must not use IDataErrorInfo nor throw Exception for use with ExceptionValidationRule  Instead you can    Use custom ValidationRule  Define a partial class in your WPF UI project and implements IDataErrorInfo

User · Answer

You might be interested in the BookLibrary sample application of the WPF Application Framework  WAF   It shows how to use validation in WPF and how to control the Save button when validation errors exists

User · Answer

From MS s Patterns  amp  Practices documentation      Data Validation and Error Reporting      Your view model or model will often be   required to perform data validation   and to signal any data validation   errors to the view so that the user   can act to correct them       Silverlight and WPF provide support   for managing data validation errors   that occur when changing individual   properties that are bound to controls   in the view  For single properties   that are data-bound to a control  the   view model or model can signal a data   validation error within the property   setter by rejecting an incoming bad   value and throwing an exception  If   the ValidatesOnExceptions property on   the data binding is true  the data   binding engine in WPF and Silverlight   will handle the exception and display   a visual cue to the user that there is   a data validation error       However  throwing exceptions with   properties in this way should be   avoided where possible  An alternative   approach is to implement the   IDataErrorInfo or INotifyDataErrorInfo   interfaces on your view model or model   classes  These interfaces allow your   view model or model to perform data   validation for one or more property   values and to return an error message   to the view so that the user can be   notified of the error    The documentation goes on to explain how to implement IDataErrorInfo and INotifyDataErrorInfo

User · Answer

personaly  i m using exceptions to handle validation  it requires following steps    in your data binding expression  you need to add  ValidatesOnException True  in you data object you are binding to  you need to add DependencyPropertyChanged handler where you check if new value fulfills your conditions - if not - you restore to the object old value  if you need to  and you throw exception   in your control template you use for displaying invalid value in the control  you can access Error collection and display exception message    the trick here  is to bind only to objects which derive from DependencyObject  simple implementation of INotifyPropertyChanged wouldn t work - there is a bug in the framework  which prevents you from accessing error collection

User · Answer

You might be interested in the BookLibrary sample application of the WPF Application Framework  WAF   It shows how to use validation in WPF and how to control the Save button when validation errors exists

User · Answer

personaly  i m using exceptions to handle validation  it requires following steps    in your data binding expression  you need to add  ValidatesOnException True  in you data object you are binding to  you need to add DependencyPropertyChanged handler where you check if new value fulfills your conditions - if not - you restore to the object old value  if you need to  and you throw exception   in your control template you use for displaying invalid value in the control  you can access Error collection and display exception message    the trick here  is to bind only to objects which derive from DependencyObject  simple implementation of INotifyPropertyChanged wouldn t work - there is a bug in the framework  which prevents you from accessing error collection

User · Answer

Also check this article  Supposedly Microsoft released their Enterprise Library  v4 0  from their patterns and practices where they cover the validation subject but god knows why they didn t included validation for WPF  so the blog post I m directing you to  explains what the author did to adapt it  Hope this helps

User · Answer

personaly  i m using exceptions to handle validation  it requires following steps    in your data binding expression  you need to add  ValidatesOnException True  in you data object you are binding to  you need to add DependencyPropertyChanged handler where you check if new value fulfills your conditions - if not - you restore to the object old value  if you need to  and you throw exception   in your control template you use for displaying invalid value in the control  you can access Error collection and display exception message    the trick here  is to bind only to objects which derive from DependencyObject  simple implementation of INotifyPropertyChanged wouldn t work - there is a bug in the framework  which prevents you from accessing error collection

User · Answer

Also check this article  Supposedly Microsoft released their Enterprise Library  v4 0  from their patterns and practices where they cover the validation subject but god knows why they didn t included validation for WPF  so the blog post I m directing you to  explains what the author did to adapt it  Hope this helps

User · Answer

Also check this article  Supposedly Microsoft released their Enterprise Library  v4 0  from their patterns and practices where they cover the validation subject but god knows why they didn t included validation for WPF  so the blog post I m directing you to  explains what the author did to adapt it  Hope this helps

User · Answer

Also check this article  Supposedly Microsoft released their Enterprise Library  v4 0  from their patterns and practices where they cover the validation subject but god knows why they didn t included validation for WPF  so the blog post I m directing you to  explains what the author did to adapt it  Hope this helps

User · Answer

If your business class is directly used by your UI is preferrable to use IDataErrorInfo because it put logic closer to their owner   If your business class is a stub class created by a reference to an WCF XmlWeb service then you can not must not use IDataErrorInfo nor throw Exception for use with ExceptionValidationRule  Instead you can    Use custom ValidationRule  Define a partial class in your WPF UI project and implements IDataErrorInfo

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