System windows forms control validating

You can validate data by handling the Cell Validating event, which is raised by the Data Grid View when the current cell changes.

In this walkthrough, you will retrieve rows from the column and tries to leave the cell, the Cell Validating event handler will examine new company name string to make sure it is not empty; if the new value is an empty string, the Data Grid View will prevent the user's cursor from leaving the cell until a non-empty string is entered.

A side effect of the control maintaining focus when data is invalid is that it is impossible to close the parent form in any of the usual ways you close a form: However, in some cases, you might want to allow the user to close the form regardless of whether the values in the controls are valid. Note Modal forms do not validate the contents of controls when closed.

You can override validation and close a form that still contains invalid data by creating a handler for the form's Closing event. You can still use control validation to lock focus to a control, but you do not need to be concerned with the behavior with regard to closing the form.

You can use a Windows Forms Error Provider component to display an error icon when the user enters invalid data.

You must have at least two controls on the form in order to tab between them and thereby invoke the validation code.

You often want to check if the information users enter into a Windows Form is valid. In the event handler, you test for a certain condition (such as the phone number example from above). If the test fails, you set the Cancel property of the Validating event's Cancel Event Args to True.

For example, if you have a Text Box control for a phone number, you can check that it contains only the appropriate characters (numbers, parentheses, hyphens and so forth). For examples using regular expressions, see Regular Expression Examples. Validation is one of a series of events that occurs during processing. This cancels the Validating event and causes the focus to return to the control.

Cell Validating Dim header Text As String = _ data Grid View1.

If the event handler for the Cell Validating event finds that the value is an empty string, the Data Grid View prevents the user from exiting the cell until a non-empty string is entered.

For a complete explanation of this code example, see Walkthrough: Validating Data in the Windows Forms Data Grid View Control.

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.


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