C control validating event
This increased level of encapsulation in self-validating controls has many benefits.
For example, you can add your specialized controls to a common control library shared across many applications, contributing to a significantly higher level of code reuse.
You can use the power of inheritance and regular expressions to develop a set of Text Box-derived controls that support a variety of input.
The first step is to create a base class that serves as the foundation control.
The MFC controls don't let you enter numbers such as 1.25 or -12 if you need to. NET lacks an equivalent to the MFC numerical Edit control, but it does have rich support for inheritance with regard to Windows Forms Controls.
You can use inheritance to build an entire family of self-validating controls that go far beyond restricting input to the characters 0 through 9.
At this point the user is not allowed to cancel the performed changes, pressing the Esc key.
Let's assume that the If the user enters empty string for a specific cell and tries to navigate to another row, the validation fails and the Error Text is displayed on the corresponding row.Validation is a good candidate for encapsulation in a self-validating control if the input is independent of the rest of your application's state.Regular expressions give you powerful tools for matching structured text.Fortunately, you can address part of this deficiency yourself by building your own self-validating text input controls. NET's existing controls restrict the user input based on the type of input required.The canonical example of this type of control is a Text Box control that lets the user enter only numbers.