Question

I have a form that has 3 buttons on it: Save, Approve and Reject.

Now I need validate User’s input differently based on what button has been clicked.
For example User should be able to Save the object even if most of the fields are empty but in order to Approve some fields are required.

One approach is to put validation to CanSave and CanApprove methods (the buttons are bound to ICommand in the ViewModel). The problem here that buttons get disabled but there is no indication of which fields are required to fill to enable particular button.

Ideally all buttons should be enabled all the time and perform validation when the button is clicked. But how do I mark fields as invalid from VM?

Answer 1

Try adding something like a LastStateValidated property on your class and base your IDataErrorInfo validation off that value.

This means that the first time you load the form, the validation that appears will only be the ones that are in effect regardless of the object’s state.

When you try and execute a command, the State changes and this will make IDataErrorInfo validate differently, so different validation errors will show up based on what the last action was that the user tried executing.