C windows form validating event
When you use the Error Provider, you only need to add one to your form.
It maintains a mapping of error messages associated to each control in the form.
There is a deep discussion about when, where and how this validation should be done.
Should this validation be done on the client-side or the server-side in a client/side application?
If you set an error message for a control, then an error icon is shown next to the control and will also display a tooltip when you hover the mouse over the error icon.
You set the error message for a control by calling the Set Error method on the error provider instance.
Data-bound controls raise events when validation occurs, giving the opportunity to write validation logic.As well as the Error Provider component notifies the user of any validation problems.