The FormClosing event occurs as the form is being closed. When a form is closed, it is disposed, releasing all resources associated with the form. If you cancel this event, the form remains opened. To cancel the closure of a form, set the Cancel property of the FormClosingEventArgs passed to your event handler to true.

When a form is displayed as a modal dialog box, clicking the Close button (the button with an X at the upper-right corner of the form) causes the form to be hidden and the DialogResult property to be set to DialogResult.Cancel. You can override the value assigned to the DialogResult property when the user clicks the Close button by setting the DialogResult property in an event handler for the FormClosing event of the form.

Note:
When the Close method is called on a Form displayed as a modeless window, you cannot call the Show method to make the form visible, because the form's resources have already been released. To hide a form and then make it visible, use the Hide method.

If the form is a multiple-document interface (MDI) parent form, the FormClosing events of all MDI child forms are raised before the MDI parent form's FormClosing event is raised. Likewise, the FormClosed events of all MDI child forms are raised before the FormClosed event of the MDI parent form is raised. Canceling the FormClosing event of an MDI child form does not prevent the FormClosing event of the MDI parent form from being raised. However, canceling the event will set to true the Cancel property of the FormClosingEventArgs class that is passed as a parameter to the parent form. To force all MDI parent and child forms to close, set the Cancel property to false in the MDI parent form.

For more information about handling events, see Consuming Events.

The following code example demonstrates the use of this member. In the example, an event handler reports on the occurrence of the FormClosing 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 Form named Form1. Then ensure that the event handler is associated with the FormClosing event.

Private Sub Form1_FormClosing(sender as Object, e as FormClosingEventArgs) _ 
     Handles Form1.FormClosing

    Dim messageBoxVB as New System.Text.StringBuilder()
    messageBoxVB.AppendFormat("{0} = {1}", "CloseReason", e.CloseReason)
    messageBoxVB.AppendLine()
    messageBoxVB.AppendFormat("{0} = {1}", "Cancel", e.Cancel)
    messageBoxVB.AppendLine()
    MessageBox.Show(messageBoxVB.ToString(),"FormClosing Event")

End Sub

private void Form1_FormClosing(Object sender, FormClosingEventArgs e) {

System.Text.StringBuilder messageBoxCS = new System.Text.StringBuilder();
messageBoxCS.AppendFormat("{0} = {1}", "CloseReason", e.CloseReason );
messageBoxCS.AppendLine();
messageBoxCS.AppendFormat("{0} = {1}", "Cancel", e.Cancel );
messageBoxCS.AppendLine();
MessageBox.Show(messageBoxCS.ToString(), "FormClosing Event" );
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

.NET Framework

Reference

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