Detecting MDI Child Window Activation
4.4.4 Detecting MDI Child Window Activation
Code in the MDI parent form class can be notified when an MDI child form becomes active inside an MDI parent form. Active means that the child form receives the input focus after another MDI child form or the MDI parent form had the input focus. To receive such notification, the MDI parent form must override the OnMdiChildActivate method defined in the Form class. For example: Place this within the class definition of the MDI parent form. Protected Overrides Sub OnMdiChildActivateByVal e As EventArgs MyBase.OnMdiChildActivatee Important ... End Sub It is important to call the base-class implementation of OnMdiChildActivate within the overriding function, so that any necessary base-class processing including raising of the MdiChildActivate event can occur. The e parameter carries no information. To find out which MDI child form became active, read the ActiveMdiChild property of the MDI parent form. This property is of type Form. Convert it to the MDI child forms type to gain access to any public members that are specific to that type. For example: Protected Overrides Sub OnMdiChildActivateByVal e As EventArgs MyBase.OnMdiChildActivatee Assumes that SomeFormType is defined elsewhere and inherits from Form. Also assumes that the MDI child forms in the application are always of this type. Dim childForm As SomeFormType = _ CTypeActiveMdiChild, SomeFormType Do something with childForm here. ... 155 End Sub To have code outside of the MDI parent form class notified when an MDI child form becomes active, write a handler for the MDI parent forms MdiChildActivate event. This event is defined in the Form class as: Public Event MdiChildActivate _ ByVal sender As Object, _ ByVal e As EventArgs _ The sender parameter is the MDI parent form, not the MDI child form that has been activated. The e parameter does not contain any additional information about the event. As when overriding the OnMdiChildActivate method, read the MDI parent forms ActiveMdiChild property to discover which MDI child form has been activated.4.5 Component Attributes
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