CancelEventArgs Class

A cancelable event is raised by a component when it is about to perform an action that can be canceled, such as the Closing event of a Form.

Note
The Closing event is deprecated and has been replaced by FormClosing. It is offered as an example here only to illustrate the usage of CancelEventArgs.

CancelEventArgs provides the Cancel property to indicate whether the event should be canceled.

Note

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: SharedState. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The following example uses CancelEventArgs and a CancelEventHandler to handle the Closing event of a Form. This code assumes that you have created a Form with a class-level Boolean variable named isDataSaved. It also assumes that you have added a statement to invoke the OtherInitialize method from the form's Load method or the constructor (after the call to InitializeComponent).

// Call this method from the constructor of your form 
    private void OtherInitialize() {
       this.Closing += new CancelEventHandler(this.Form1_Closing);
       // Exchange commented line and note the difference. 
       this.isDataSaved = true;
       //this.isDataSaved = false;
    }

    private void Form1_Closing(Object sender, CancelEventArgs e) {
       if (!isDataSaved) {
          e.Cancel = true;
          MessageBox.Show("You must save first.");
       }
       else {
          e.Cancel = false;
          MessageBox.Show("Goodbye.");
       }
    }
 

.NET Framework

.NET Framework Client Profile

Portable Class Library

.NET for Windows Store apps

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)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Reference