Occurs when the user's input or assigned character does not match the corresponding format element of the input mask.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
is the default event for the MaskedTextBox class.
The event occurs when a character is rejected by the input mask. The input mask, represented by the Mask property, is interpreted by the masked text provider associated with the control through the MaskedTextProvider property. is raised in the following situations:
An input character does not match the corresponding format element. For example, the user enters an alphabetic character when a digit is required. This is probably the most common reason why this event is raised.
The user is trying to input extraneous characters beyond the end of the mask either because the mask has already been filled or the current caret position has been moved to the very end of the displayed input mask string.
A paste operation either inserts a character that does not match its associated format element, or if the IsOverwriteMode property is false, it shifts existing characters into new positions where they do not match their format elements.
A cut operation shifts existing characters to the left, and one or more characters do not match their newly associated format elements.
An assignment was made to the Text property and the assigned string caused one or more mask violations.
If a string was assigned to the control that causes to occur, no part of the string will appear in MaskedTextBox.
The default handling for will play a beep sound if the BeepOnError property is set to true. This event is often handled to implement custom error handling, for example, to move to the next user input control if the mask is full, or to display a custom error dialog box or ToolTip if the input character is invalid.
The following code example demonstrates the use of this member. In the example, an event handler reports on the occurrence of the event. This report helps you to learn when the event occurs and can assist you in debugging. To report on multiple events or on events that occur frequently, consider replacing MessageBox.Show with Console.WriteLine or appending the message to a multiline TextBox.
To run the example code, paste it into a project that contains an instance of type MaskedTextBox named MaskedTextBox1. Then ensure that the event handler is associated with the event.
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)