Question

From my reading and trying to understand and implement MVVM and validation, I need some help on the following scenario.

View – User interface (expected)

Model – based on a data table, and via OnColumnChanging, tests for validation requirements on a column-by-column basis (this part works no problem)

ViewModel – glue the connects the model to the view, this works too.

For each of the textbox controls, I have them respectively binding two-way to the data table, current row (still no problem) and it shows the data as expected. The flags including: NotifyOnTargetUpdated, ValidatesOnDataErrors, ValidatesOnExceptions and NotifyOnValidationError are all set to true.

If I use the interface and put in invalid value, it properly triggers the validation and puts red border around control showing it failed.

Now the problem. I start my form, and click the “Add” button (new record, blank values), textbox controls now enabled for editing content. Click the “Save” button. I want to have all the controls refreshed that are missing “required” data. Since my view model is bound to columns of the data table, and that from my readings, all the validation should be handled in the viewmodel, how should I adjust my scenario.

I don’t know how to force which controls are bound to respective controls when they’ve never received focus. In addition, from other readings, to allow for unit testing, you should be able to test under the assumption that there is never a user interface. So, in theory, I could automate creating my viewmodel, which loads my data model, adds a record, tries to save and forces whatever to test all “required” fields.

Am I close??? way off??? Not quite positive on this.

Answer 1

Implement: IDataErrorInfo and check Error within your SaveCommand

Further Reading:

• WPF Apps With The Model-View-ViewModel Design Pattern
• Using IDataErrorInfo for validation in MVVM with Silverlight and WPF