If you determine that the control's data is not valid, you can cancel the Validating event by setting this object's Cancel property to .If you do not set the Cancel property, Windows Forms will assume that validation succeeded for that control, and raise the Validated event.A is a string made up of characters from a masking language that specifies which characters can be entered at any given position in the text box. If the user types an incorrect entry, for example, the user types a letter when a digit is required, the control will automatically reject the input.

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When users enter data into your application, you may want to verify that the data is valid before your application uses it.

You may require that certain text fields not be zero-length, that a field be formatted as a telephone number or other type of well-formed data, or that a string not contain any unsafe characters that could be used to compromise the security of a database.

In the event, set the Cancel property to Note If you force the form to close in this manner, any data in the form's controls that has not already been saved is lost.

In addition, modal forms do not validate the contents of controls when they are closed.

For example, if you have code in a Validated event that attempts to cancel the data binding, the data binding will still occur.

In this case, to perform validation in the Validated event, change the control's Data Source Update Mode property (under (Databindings)\(Advanced)) from On Validation to Never, and add So when does a control's data get validated? You can use either implicit or explicit validation, depending on the needs of your application.For a code example that validates an email address in a Text Box, see Validating.Validation is very useful when you have bound your controls to a data source, such as a database table.If you cancel the Validating event, the behavior of the control will be determined by what value that you assigned to Auto Validate.If you assigned Enable Prevent Focus Change, canceling the event will cause the Validated event not to occur.It allows you to specify required characters, optional characters, literal characters, such as hyphens and parentheses, currency characters, and date separators.