The former could confuse users when they press keys but nothing happens.
It is usually better to show their keypresses but display a warning that the input is currently invalid.
Each control that accepts free-form user input has a Validating event that will occur whenever the control requires data validation.
In the Validating event-handling method, you can validate user input in several ways.
Another efficient use of the user control is to simply preload a Combo Box or List Box with static items you commonly use in almost every application; some examples of this are countries/regions, cities, states, and office locations.
For more information about authoring custom controls, see Developing Custom Windows Forms Controls with the . You might consider creating a namespace that contains several classes of user controls and compiling it into one DLL.
The control also works well when bound to a data source.
The Format event on a data binding can be used to reformat incoming data to comply with the mask, and the Parse event can be used to reformat outgoing data to comply with the specifications of the data field. If you want full programmatic control over validation, or need to perform complex validation checks, you should use the validation events built into most Windows Forms controls.
Consistency gives your application a more polished and professional appearance.The code is intended to be compiled into a DLL for reference in other applications.Do you want to prevent input that isn't allowed or validate the input before it is possible to proceed?Occurs when the control is clicked if the Standard Click bit flag is set to true in a derived class.properties are set relative to the size of the view that the user sees, not to the total size including the unseen part.