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Ok. This seems like an incredibly basic use case but fore some reason I am having an issue finding a common solution across control types.

Heres the use case:

A form is presented to the user with any editable controls. (Text box, combo, grid etc.).

The user edits a value in the control and tabs out.
Expectation is that I can wire to an event like Lost Focus and do "foo" with the changed value.

The user then gives focus back to the control and tabs out without making an edit. Expectation is that whatever event I am wired to I can check if the value has been changed.

Is there one common event across controls that will only fire when the user has finished editing( such as tab out or enter ) and allow me to check previous state vs. current state?

Jason Burke
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    Have you tried LostFocus and KeyboardLostFocus events ? – Sisyphe Oct 19 '12 at 14:51
  • If you use binding you can use the property [NotifyOnSourceUpdated](http://msdn.microsoft.com/en-us/library/system.windows.data.binding.notifyonsourceupdated.aspx) (or Target) on the binding object itself. Another nice way to handle Forms of data, with validation and reverting are [BindingGroups](http://msdn.microsoft.com/en-us/library/system.windows.data.bindinggroup.aspx) and the [IEditableObject](http://msdn.microsoft.com/en-us/library/system.componentmodel.ieditableobject.aspx). But the best would be to start with the basics of WPF. – dowhilefor Oct 19 '12 at 15:29
  • The only event I can thikn of that shows both the previous value and the current value is the `TextChanged` event of a `TextBox`. I'd highly recommend you set your form's `DataContext` to a class that implements `INotifyPropertyChanged`, and bind your form's controls to that class' properties. That way, you can handle any change logic in your code instead of having to try and figure out a XAML event for it. – Rachel Oct 19 '12 at 16:17

4 Answers4

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Jason, you may want to look into Binding and DependencyProperties in WPF instead of tracking events in your form. You would bind a class to your form which exposes properties to be changed. Using DependancyProperties a single event is fired called "PropertyChanged".

Unfortunately is is a broad topic, but you will really get the full benefit of the WPF programming model. Searches on "dependency properties in wpf" will give you some good examples.

Spevy
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I think maybe this is Focus issue. There exist two different focus types: keyboard focus and logical focus. The the control that has keyboard focus is the one that has the caret, in what the user press a key and the control process that input. The a control may have the logical focus but not having the keyboard focus. Please check this in the MSDN article "Input Overview". About the other question, maybe you could process the TabControl.SelectedItemChanged for taking the event when a tab item selection changed. Hope this is helpful to you...

Raúl Otaño
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What you may be interested in is implementing INotifyPropertyChanging (not just INotifyPropertyChanged).

As noted in the answer of this question, the INotifyPropertyChangING does not prevent you from changing a value, but to detect WHEN something DOES change, and what it's new value is going to be.

Hope it helps in your solution needs.

Community
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DRapp
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As the previous answers suggested, you would be better off by implementing a view - viewmodel structure, with your viewmodel having implemented INotifyPropertyChanged, and thus allowing you to bind to properties that will announce their changes to the UI.

If you don't want to do this, you can eventually subscribe on your input elements to the PreviewKeyUp event, check if the Tab key has been pressed and proceed from there.

Avram Tudor
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