Occurs when a multiple-document interface (MDI) child form is activated or closed within an MDI application.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
You can use this event to perform tasks such as updating the contents of the MDI child form and changing the menu options available in the MDI parent form based on the status of the MDI child form that is activated.
For more information about handling events, see Handling and Raising Events.
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 Form named Form1. 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)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.