ScrollBar.OnValueChanged Method (EventArgs)


Raises the ValueChanged event.

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

Protected Overridable Sub OnValueChanged (
	e As EventArgs


Type: System.EventArgs

An EventArgs that contains the event data.

Raising an event invokes the event handler through a delegate. For more information, see NIB: Raising an Event.

The OnValueChanged method also allows derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.

Notes to Inheritors:

When overriding OnValueChanged in a derived class, be sure to call the base class’s OnValueChanged method so that registered delegates receive the event.

The following code example uses the derived class VScrollBar. Event handlers for the Scroll and ValueChanged events are created. This code assumes that a Label and Button have been created on a form and that the button has an event handler for the Click event. When the button is clicked, the Value property of the scroll bar is adjusted in code. The label will display the current value of the Value property and the event that changed it. You will notice that when the scroll value is changed by the button's Click event, only the ValueChanged event is raised. In contrast, when the scroll bar is scrolled manually, the Scroll event is raised immediately after the ValueChanged event.


For instructions about how to run this example in Visual Studio, see How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio.

Private Sub AddMyScrollEventHandlers()
    ' Create and initialize a VScrollBar.
    Dim vScrollBar1 As New VScrollBar()

    ' Add event handlers for the OnScroll and OnValueChanged events.
    AddHandler vScrollBar1.Scroll, AddressOf Me.vScrollBar1_Scroll
    AddHandler vScrollBar1.ValueChanged, AddressOf Me.vScrollBar1_ValueChanged
End Sub    

' Create the ValueChanged event handler.
Private Sub vScrollBar1_ValueChanged(sender As Object, e As EventArgs)
    ' Display the new value in the label.
    label1.Text = "vScrollBar Value:(OnValueChanged Event) " & _
End Sub    

' Create the Scroll event handler.
Private Sub vScrollBar1_Scroll(sender As Object, e As ScrollEventArgs)
    ' Display the new value in the label.
    label1.Text = "VScrollBar Value:(OnScroll Event) " & _
End Sub    

Private Sub button1_Click(sender As Object, e As EventArgs)
    ' Add 40 to the Value property if it will not exceed the Maximum value.
    If vScrollBar1.Value + 40 < vScrollBar1.Maximum Then
        vScrollBar1.Value = vScrollBar1.Value + 40
    End If
End Sub

.NET Framework
Available since 1.1
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