Form.ActiveMdiChild Property


Gets the currently active multiple-document interface (MDI) child window.

Namespace:   System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

Public ReadOnly Property ActiveMdiChild As Form

Property Value

Type: System.Windows.Forms.Form

Returns a Form that represents the currently active MDI child window, or null if there are currently no child windows present.

You can use this method to determine whether there are any MDI child forms open in your MDI application. You can also use this method to perform operations on an MDI child window from its MDI parent form or from another form that is displayed in your application.

If the currently active form is not an MDI child form, you can use the ActiveForm property to obtain a reference to it.

The following code example obtains a reference to the active MDI child form and loops through all TextBox controls on the form, resetting their Text properties. This example requires that an MDI parent form has been created and that this method call is being made from the MDI parent form.

Public Sub ClearAllChildFormText()
    ' Obtain a reference to the currently active MDI child form.
    Dim tempChild As Form = Me.ActiveMdiChild

    ' Loop through all controls on the child form.
    Dim i As Integer
    For i = 0 To tempChild.Controls.Count - 1
        ' Determine if the current control on the child form is a TextBox.
        If TypeOf tempChild.Controls(i) Is TextBox Then
            ' Clear the contents of the control since it is a TextBox.
            tempChild.Controls(i).Text = ""
        End If
    Next i
End Sub 'ClearAllChildFormText

.NET Framework
Available since 1.1
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