User Input Validation in Windows Forms

Validating textbox csharp

If the user types an

If you want to use implicit validation for a control, you must set that control's AutoValidate property to true. It allows you to specify required characters, optional characters, literal characters, such as hyphens and parentheses, currency characters, and date separators.

The following table shows the most common controls and their defaults. It then uses a regular expression to make sure the entered text has the format or -. Data Binding and Event-Driven Validation Validation is very useful when you have bound your controls to a data source, such as a database table. The masking language that is used by MaskedTextBox is very flexible.

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. You can use either implicit or explicit validation, depending on the needs of your application. None of the other TextBoxes gets the focus so their Validating event handlers never get a chance to run so the form closes. The event triggers even if the user tries to close the form. When the user tries to move out of a TextBox, its Validating evnet fires.

None of the

User Input Validation in Windows Forms

You can use eitherThe event triggers even

Cancel parameter to true to prevent focus from leaving the first control. 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 true. Implicit Validation The implicit validation approach validates data as the user enters it. Important If you have custom validation that takes place after the Validating event, it will not affect the data binding.

Explicit Validation The explicit validation approach validates data at one time. The event handler checks whether the TextBox contains valid text and, if it does not, sets e.

Return true if the

The Validating event is supplied an object of type CancelEventArgs. The event handler presents the char that failed validation f. For example, if you have code in a Validated event that attempts to cancel the data binding, the data binding will still occur.

When the user tries

Then you can add the assembly containing my control to the list of. Input focus will remain on the current control until the user changes the data to a valid input. For more information, see MaskedTextBox Control. Call Validate to validate the last control to have lost focus. WriteValue to your validation code.

To validate your controls, you will have to use explicit validation. If you do not set the Cancel property, Windows Forms will assume that validation succeeded for that control, and raise the Validated event. This event gets fired whenever the ValidationMode Property has been changed.

Return true if the field is valid. This is up to you, the developer. Call a custom method to validate the data in the controls manually.