C control on validating
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.If you do not set the Cancel property, Windows Forms will assume that validation succeeded for that control, and raise the Validated event.For a code example that validates an email address in a Text Box, see Validating.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.Windows Forms provides several ways for you to validate input in your application.For example, if you have a text box that must contain a postal code, you can perform the validation in the following ways: The Validating event is supplied an object of type Cancel Event Args.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 .
By using validation, you can make sure that your control's data satisfies the format required by the data source, and that it does not contain any special characters such as quotation marks and back slashes that might be unsafe.
The DTD is retrieved automatically based on the DOCTYPE of the parsed document.
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If you need to require users to enter data in a well-defined format, such as a telephone number or a part number, you can accomplish this quickly and with minimal code by using the Masked Text Box control.
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.